Dear Colleagues, - Department of Chemistry [FSU] 2000-2001.doc · Web viewDear Colleagues, here is,...

Dear Colleagues,

here is, late as always, but hopefully still of interest, a list of references for the field of “Polyelectrolyte Multilayers”.

It covers the year 2000 and January to June of 2001. It is based on a Science Citation Search using the (in my opinion) 50 most important references of the field. Subsequently, I have manually taken out all references that do not clearly belong to the field or that are too borderline.

The result is a list with 257 references, I hope that it will help us all to see what has recently been done and where the field is going. I will try to update this list on a (hopefully) regular base and I will try to complete it for the years 1998 and 1999. If major differences with lists such as found on the poly-electrolyte multilayer homepage http://www.chem.fsu.edu/multilayers/ will show up, the search algorithm will be refined.

Of course, nobody is perfect, so I would like to apologize to all of you if work from your group should be included, but for some reason has been over-looked. In this case I would appreciate to receive the missing reference, preferably as Acrobat document (PDF file) via [email protected] . Please also let me know if there are references that should not be in this list.

In the meantime we are looking forward to the publication of a reference book on “Thin Films – Polyelectrolyte Multilayers and Related Multicomposites” by VCH – Wiley and to the next symposium “Multi-Layered Polyelectrolyte-Based

Materials: Synthesis, Characterization and Applications”, organized by Merlin Bruening, Frank Caruso and Nicholas Kotov. The symposium will be held on April 7-11, 2002 in Orlando under the auspices of the 223rd American Chemical Society National Meeting.

Gero Decher

[1] Surface Modification of Microporous Polypropylene Membranes by Polyelectrolyte MultilayersT. Rieser, K. Lunkwitz, S. Berwald, J. Meierhaack, M. Muller, F. Cassel, Z. Dioszeghy and F. SimonACS SYMP SER 744 (2000), 189-204

Plasma-induced grafting of ionic monomers onto hydrophobic polypropylene membranes led to permanently charged surfaces. In addition, polyelectrolyte multilayers were built up by alternating adsorption of oppositely charged polyelectrolytes onto the grafted membrane surface. The modified membranes were characterized by FTIR-ATR and XPS. Streaming potential measurements were used to determine the electrokinetic properties of the charged surfaces. Filtration experiments were performed with human serum albumin (HSA) solutions to study the fouling behavior of the membranes. Membrane surfaces and the protein were both negatively charged under the applied conditions. The irreversible adsorption of HSA decreased remarkably for membranes that were modified by polyelectrolyte multilayers, as compared to untreated and plasma-treated samples.

[2] Controlled Precipitation of Dyes into Hollow Polyelectrolyte Capsules Based on Colloids and BiocolloidsG. Sukhorukov, L. Dähne, J. Hartmann, E. Donath and H. MöhwaldAdv. Mater. 12(2) (2000), 112-115

[3] Nanoengineering and Microengineering - 3-Dimensional Colloidal Photonic Crystals Prepared from Submicrometer-Sized Polystyrene Latex Spheres Pre-Coated with Luminescent Polyelectrolyte/ Nanocrystal ShellsA. Rogach, A. Susha, F. Caruso, G. Sukhorukov, A. Kornowski, S. Kershaw, H. Möhwald, A. Eychmuller and H. WellerAdv. Mater. 12(5) (2000), 333

Colloidal photonic crystals doped with luminescent semiconductor nanocrystals are prepared here by a layer-by- layer deposition technique. This method, which involves the consecutive electrostatic adsorption of polyelectrolyte and nanocrystals such as CdTe onto submicrometer-sized polystyrene latex globules (see Figure), is described as being very Versatile and can be extended to the fabrication of either optically active or passive shells of different thickness.

[4] Core-Shell Microspheres of a Catalytically Active Rhodium Complex Bound to a Polyelectrolyte-Coated LatexS. Mecking and R. ThomannAdv. Mater. 12(13) (2000), 953

A strategy for the immobilization of catalytically active transition metal complexes is described in which the rhodium hydride complex [(H)Rh(CO)(NaTPPTS)(3)] is electrostatically bound to highly charged polystyrene microspheres coated with cationic polyelectrolyte (see Figure). The catalytic activity of this latex-bound catalyst in the hydroformylation of methyl acrylate is reported and compared with its unbound equivalent.

[5] Large Photoinduced Birefringence in Azo Dye/Polyion Films Assembled by Electrostatic Sequential AdsorptionS. P. Bian, J. A. He, L. Li, J. Kumar and S. K. TripathyAdv. Mater. 12(16) (2000), 1202-1205

[6] Self-Assembled Diode Junctions Prepared from a Ruthenium Tris(Bipyridyl) Polymer, N-Type TiO2 Nanoparticles, and Graphite Oxide SheetsT. Cassagneau, J. H. Fendler, S. A. Johnson and T. E. MalloukAdv. Mater. 12(18) (2000), 1363-1366

[7] Fast Magic-Angle-Spinning and Double-Quantum H-1 Solid-State NMR-Spectroscopy of Polyelectrolyte MultilayersL. N. J. Rodriguez, S. M. Depaul, C. J. Barrett, L. Reven and H. W. SpiessAdv. Mater. 12(24) (2000), 1934

Polyelectrolyte Multilayer References (Jan. 2000 – June 2001), page - 1 -

Polyelectrolyte multilayers on silica colloids are investigated here using a combination of fast magic-angle spinning (MAS) and double-quantum (DQ) solid-state H-1 NMR techniques. 2D DQ H-1 NMR spectra of the bulk complex and the multilayer films (see Figure) are found to be similar, revealing complexation between the alternating layers of poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC).

[8] Multilayered Polymer Nanocapsules Derived from Gold Nanoparticle TemplatesD. I. Gittins and F. CarusoAdv. Mater. 12(24) (2000), 1947

Multilayered polymer nanocapsules have been fabricated via the sequential adsorption of oppositely charged polyelectrolytes onto gold nanoparticles followed by dissolution of the gold core in cyanide solution. The Figure shows a gold nanoparticle coated with eight polyelectrolyte layers.

[9] Multilayered Assembly of Dendrimers with Enzymes on Gold - Thickness-Controlled Biosensing InterfaceH. C. Yoon and H. S. KimAnal. Chem. 72(5) (2000), 922-926

A new approach to construct a multilayered enzyme film on the Au surface for use as a biosensing interface is described, The film was prepared by alternate layer-by-layer depositions of G4 poly(amidoamine) dendrimers and periodate-oxidized glucose oxidase (GOx), The cyclic voltammograms obtained from the Au electrodes modified with the GOx/dendrimer multilayers revealed that bioelectrocatalytic response is directly correlated to the number of deposited bilayers, that is, to the amount of active enzyme immobilized on the Au electrode surface. From the analysis of voltammetric signals, the coverage of active enzyme per GOx/dendrimer bilayer during the multilayer-forming steps was estimated, which demonstrates that the multilayer is constructed in a spatially ordered manner. Also, with the ellipsometric measurements, a linear increment of the film thickness was registered, supporting the formation of the proposed multilayered structure. The E5D5 electrode showed the sensitivity of 14.7 mu A.mM(-1) glucose.cm(-2) and remained stable over 20 days under day-by-day calibrations. The proposed method is simple and would be applicable to the constructions of thickness- and sensitivity-controllable biosensing interfaces composed of multienzymes as well as a single enzyme.

[10] Glucose and Lactate Biosensors Based on Redox Polymer/ Oxidoreductase Nanocomposite Thin-FilmsK. Sirkar, A. Revzin and M. V. PishkoAnal. Chem. 72(13) (2000), 2930-2936

Glucose and lactate enzyme electrodes have been fabricated through the deposition of an anionic self-assembled monolayer and subsequent redox polymer/enzyme electrostatic complexation on gold substrates. These surfaces were functionalized with a negative charge using 11-mercaptoundecanoic acid (MUA), followed by alternating immersions in cationic redox polymer solutions and anionic glucose oxidase (GOX) or lactate oxidase (LAX) solutions to build the nanocomposite structure. The presence of the multilayer structure was verified by ellipsometry and sensor function characterized electrochemically. Reproducible analyte response curves from 2 to 20 mM (GOX) and 2-10 mM (LAX) were generated with the standard deviation between multiple sensors between 12 and 17%, a direct result of the reproducibility of the fabrication technique. In the case of glucose enzyme electrodes, the multilayer structure was further stabilized through the introduction of covalent bonds within and between the layers. Chemical cross-linking was accomplished by exposing the thin film to glutaraldehyde vapors, inducing linkage formation between lysine and arginine residues present on the enzyme periphery with amine groups present on a novel redox polymer, poly[vinyl-pyridine Os(bisbipyridine)(2)Cl]-co-allylamine. Finally, an initial demonstration of thin-film patterning was per formed as a precursor to the development of redundant sensor arrays. Microcontact printing was used to functionalize portions of a gold surface with a blocking agent, typically 1- hexadecanethiol. This was followed by immersion in MUA to functionalize the remaining portions of gold with negative charges. The multilayer deposition process was then followed, resulting in growth only on the regions containing MUA, resulting in a ''positive''-type pattern. This technique may be used for fabrication of thin-film redundant sensor arrays, with thickness under 100 Angstrom and lateral dimensions on a micrometer scale.

[11] In-Situ Assembled Mass-Transport Controlling Micromembranes and Their Application in Implanted Amperometric Glucose Sensors


T. Chen, K. A. Friedman, I. Lei and A. HellerAnal. Chem. 72(16) (2000), 3757-3763

Micromembranes were assembled by sequentially chemisorbing polyanions and polycations on miniature (5 x 10(-4) cm(2)) enzyme electrodes. The sequential chemisorption process allowed the simultaneous tailoring of their sensitivity, dynamic range, drift, and selectivity. When assembled on tips of 250-mu m- diameter gold wires coated with redox polymer-''wired'' glucose oxidase, they allowed tailoring of the glucose electrodes for >2 nA/mM sensitivity; 0-30 mM dynamic range; drift of less than or equal to 5% per 24 h at 37 degrees C at 15 mM glucose concentration; and 15% current increment by the combination of 0.1 mM ascorbate, 0.2 mM acetaminophen, and 0.5 mM urate, The membranes also retained transition metal ions that bound to and damaged the redox polymer ''wiring'' the enzyme. The electrodes were tested in the jugular veins and in the intrascapular subcutaneous region of anaesthetized and heparinized nondiabetic Sprague-Dawley rats, in which rapid changes of glycemia were forced by intravenous injections of glucose and insulin. After one-point in vivo calibration of the electrodes, all of the 152 data points were clinically accurate when it was assumed that after insulin injection the glycemia in the subcutaneous fluid lags by 9 min behind that of blood withdrawn from the insulin-injected vein.

[12] Plastic Microfluidic Devices Modified with Polyelectrolyte MultilayersS. L. R. Barker, M. J. Tarlov, H. Canavan, J. J. Hickman and L. E. LocascioAnal. Chem. 72(20) (2000), 4899-4903

Control of the polymer surface chemistry is a crucial aspect of development of plastic microfluidic devices. When commercially available plastic substrates are used to fabricate microchannels, differences in the EOF mobility from plastic to plastic can be very high. Therefore, we have used polyelectrolyte multilayers (PEMs) to alter the surface of microchannels fabricated in plastics. Optimal modification of the microchannel surfaces was obtained by coating the channels with alternating layers of poly(allylamine hydrochloride) and poly(styrene sulfonate). Polystyrene (PS) and poly(ethylene terephthalate) glycol (PETG) were chosen las substrate materials because of the significant differences in the polymer chemistries and in the EOF of channels fabricated in these two plastic materials. The efficacy of the surface modification has been evaluated using XPS and by measuring the EOF mobility. When microchannels prepared in both PS and PETG are modified with PEMs, they demonstrate very similar electroosmotic mobilities. The PEMs are easily fabricated and provide a means for controlling the now direction and the electroosmotic mobility in the channels. The PEM-coated microchannels have excellent wettability, allowing facile filling of the channels. In addition, the PEMs produce reproducible results and are robust enough to withstand long-term storage.

[13] Electrochemical-Behavior of Polyphenol Oxidase Immobilized in Self-Assembled Structures Layer-by-Layer with Cationic PolyallylamineE. S. Forzani, V. M. Solis and E. J. CalvoAnal. Chem. 72(21) (2000), 5300-5307

We report here a novel bioelectrode based on self-assembled multilayers of polyphenol oxidase intercalated with cationic polyallylamine built up on a thiol-modified field surface. We use an immobilization strategy previously described by Hodak J, et al. (Langmuir 1997, 13, 2708-2716) Quartz crystal microbalance with electro-acustic impedance experiments were carried out to follow quantitatively the multilayer film formation. The response of the self-assembly polyphenol oxidase- polyallylamine electrodes toward different metabolically related cate-cholamines was studied, to evaluate enzyme kinetics. For the analyzed compounds, only dopamine and its metabolite Dopac gave catalytic currents at applied potential close to 0V. These responses were proportional to the number of polyphenol oxidase-immobilized layers and were also controlled by the enzymatic reaction. The combination of microgravimetric and electrochemical techniques allowed us to determine the kinetic enzymatic constants, showing that the decomposition rate for the enzyme-substrate complex is slower than the enzymatic reoxidation step.

[14] Control of Flow Direction in Microfluidic Devices with Polyelectrolyte MultilayersS. L. R. Barker, D. Ross, M. J. Tarlov, M. Gaitan and L. E. LocascioAnal. Chem. 72(24) (2000), 5925-5929

Electroosmotic flow (EOF) is commonly utilized in microfluidics. Because the direction of the EOF can be determined by the substrate surface charge, control of the surface chemical state offers the potential, in addition to voltage control, to direct the flow in microfluidic devices. We report the use of polyelectrolyte multilayers (PEMs) to alter the surface charge and control the direction of how in polystyrene and acrylic microfluidic devices. Relatively complex now patterns with simple arrangements of applied voltages are realized by derivatization of different arms of


a single device with oppositely charged polyelectrolytes. In addition, flow in opposite directions in the same channel is possible. A positively derivatized plastic substrate with a negatively charged lid was used to achieve top-bottom opposite flows. Derivatization of the two sides of a plastic microchannel with oppositely charged polyelectrolytes was used to achieve side-by-side opposite flows. The flow is characterized using fluorescence imaging and particle velocimetry.

[15] A Novel-Approach of Antibody Immobilization Based on N-Butyl Amine Plasma-Polymerized Films for ImmunosensorsZ. Y. Wu, Y. H. Yan, G. L. Shen and R. Q. YuAnal. Chim. Acta. 412(1-2) (2000), 29-35

A novel method based on plasma-polymerized films (PPFs) is proposed for immobilizing antibodies (antigens) through a polyelectrolyte-mediated layer. The immobilization of goat-anti- IgG antibody, as an example, is investigated. The n-butyl amine PPFs are deposited on the surfaces of quartz crystal microbalance (QCM) with a radio frequency plasma method using n- butyl amine as the precursor, the IR spectrum indicating the existence of amino-groups in the film. After self-assembling a polystyrenesulfonate (PSS) layer on the PPF, the goat-anti-IgG antibody is immobilized in a 0.2 mg ml(-1) of antibody immobilizing solution at pH 5.0. The QCM immunosensor can quantitatively determine NH IgG in the range of 0.7-126 mu g ml(-1). Moreover, the PSS and protein layers can easily be removed simply by shifting the pH, making the immunosensor regenerable. (C) 2000 Elsevier Science B.V. All rights reserved.

[16] Layer-by-Layer Assembly of Multilayer Films Consisting of Silicotungstate and a Cationic Redox Polymer on 4-Aminobenzoic Acid Modified Glassy-Carbon Electrode and Their Electrocatalytic EffectsL. Cheng, J. Y. Liu and S. J. DongAnal. Chim. Acta. 417(2) (2000), 133-142

A novel 4-aminobenzoic acid (4-ABA) monolayer film is formed on glassy carbon electrode (GCE) by amino cation radical method. Silicotungstic heteropolyanion (SiW12O404-, denoted as SiW12)- containing multilayer films have been fabricated on the 4-ABA modified GCE surface by alternate deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)(2)Cl](2+/+) (denoted as QPVP-Os). Cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and X-ray reflectivity (XR) have been used to characterise the as- prepared multilayer films. It is proved that the multilayer films are uniform and stable. The average thickness for a bilayer of QPVP-Os/SiW12 in the multilayer film is 30.2 Angstrom. The electrocatalytic activities of the multilayer films have been investigated on the reduction of three substrates of important analytical interests, HNO2, BrO3- and H2O2. Especially, the influence of layer number of the multilayer films on the electrocatalytic reduction of HNO2 has been investigated in detail. (C) 2000 Elsevier Science B.V. All rights reserved.

[17] Fabrication of Multilayer Films Containing Horseradish- Peroxidase and Polycation-Bearing Os Complex by Means of Electrostatic Layer-by-Layer Adsorption and Its Application as a Hydrogen-Peroxide SensorW. J. Li, Z. Wang, C. Q. Sun, M. Xian and M. Y. ZhaoAnal. Chim. Acta. 418(2) (2000), 225-232

Layer-by-layer (LBL) assembled multilayer films were obtained on the surface of quartz slides and gold electrode by alternating deposition of negatively charged horseradish peroxidase (HRP) and quaternized poly(4-vinylpyridine) complexed of (Os(bpy)(2)Cl)(+/2+) (PVP-Os). The assembly process was monitored by UV-VIS spectroscopy. The electrochemical behavior of the enzyme electrode showed that multilayer films containing the enzyme and the redox polymer were highly stable. Mediator PVP-Os in the multilayer films as electron shuttle was able to transfer electrons successfully between the active center of the immobilized HRP and the electrode surface. The enzyme electrode of multilayer films was sensitive for the electrocatalytic reduction of hydrogen peroxide and can be used as amperometric sensors for hydrogen peroxide. (C) 2000 Elsevier Science B.V. All rights reserved.

[18] Polyelectrolyte Multilayer Film-Coated Electrodes for Amperometric Determination of Hydrogen-Peroxide in the Presence of Ascorbic-Acid, Uric-Acid and AcetaminophenT. Hoshi, H. Saiki, S. Kuwazawa, Y. Kobayashi and J. AnzaiAnal. Sci. 16(10) (2000), 1009-1010


[19] Probing Protein-Peptide-Protein Molecular Architecture by Atomic-Force Microscopy and Surface-Plasmon ResonanceM. M. Stevens, S. Allen, W. C. Chan, M. C. Davies, C. J. Roberts, S. J. B. Tendler and P. M. WilliamsAnalyst 125(2) (2000), 245-250

We demonstrate the creation of a protein multilayer which utilises the high affinity interaction between streptavidin and biotin and incorporates a peptidic spacer. Surface plasmon resonance measurements enabled us to monitor the construction of the multilayer in real time. Atomic force microscopy was utilised to determine surface functionality at each stage of the multilayer construction, allowing us to investigate the associated mechanical properties. In this context we observed an increase in biomolecular stretching on the formation of the multilayer. We demonstrate, utilising circular dichroism, that variations in the solvent can affect the secondary structure of the peptide linker and hence its mechanical properties. Trifluoroethanol titrations on the assembled system indicate that the multilayer properties are also stimuli responsive with regard to solvent conditions. These results indicate that the multilayer stretch before cleavage is increased in the presence of trifluoroethanol. This was not expected from the study of the individual linker alone, indicating the need to study the system as a whole as opposed to the isolated components.

[20] Synthesis of Geometrically Well-Defined, Molecularly Thin Polymer-FilmsW. T. S. Huck, A. D. Stroock and G. M. WhitesidesAngew. Chem., Int. Ed. Engl. 39(6) (2000), 1058

[21] Stepwise Assembled Photoactive Films Containing Donor-Linked FullerenesC. P. Luo, D. M. Guldi, M. Maggini, E. Menna, S. Mondini, N. A. Kotov and M. PratoAngew. Chem., Int. Ed. Engl. 39(21) (2000), 3905

[22] Photovoltaic Heterostructure Devices Made of Sequentially Adsorbed Poly(Phenylene Vinylene) and Functionalized C-60H. Mattoussi, M. F. Rubner, F. Zhou, J. Kumar, S. K. Tripathy and L. Y. ChiangAppl. Phys. Lett. 77(10) (2000), 1540-1542

We report on the preparation and characterization of rectifying photovoltaic heterostructure devices made of poly(phenylene vinylene), PPV, and C-60. The heterojunctions were built from solution using the technique of layer-by-layer sequential adsorption. This technique permits one to control the heterostructure at the molecular scale. Upon illumination with a laser beam, the devices showed large photoresponses (current and voltage) that resulted from a photoinduced electron transfer between the PPV (donor layer) and the C-60 (acceptor layer). The photocurrent was found to increase with the laser power and with the photon energy of the incident radiation. Also, a constant high photovoltage response of similar to 700- 800 mV was measured. Analysis of the time dependence of the photocurrent rise and decay, when the device was illuminated with a modulated square wave signal (chopped laser beam), permitted us to draw an analogy between the present heterojunction and a circuit made of a capacitor and a resistance in series. (C) 2000 American Institute of Physics. [S0003-6951(00)03236-8].

[23] Optical-Properties of Self-Assembled Thin-Film of Poly(P- Phenylene Vinylene)S and Its Application to Light-Emitting Devices with Microring GeometryT. Sonoda, T. Fujisawa, A. Fujii and K. YoshinoAppl. Phys. Lett. 76(22) (2000), 3227-3229

Periodic multilayer structures of poly(p-phenylene vinylene)s have been fabricated by a self-assembly method on flat surfaces and round surfaces of optical fibers. Alternating multilayers consisting of poly{1,4-[2-(5-carboxypentyloxy)-5- methoxyphenylene]vinylene} (CPMOPPV) and poly(p-phenylene vinylene) (PPV) were adsorbed onto the positively charged substrates. The optical properties of the periodic multilayer structures of CPMOPPV/PPV have been studied. Periodic multilayers with microring geometry have also been fabricated around the quartz fibers. Their optical properties have been studied, and yellow electroluminescence from a light-emitting device with microring geometry has been observed. (C) 2000 American Institute of Physics. [S0003-6951(00)03822-5].


[24] Surface-Relief Gratings from Electrostatically Layered Azo-Dye FilmsJ. A. He, S. P. Bian, L. Li, J. Kumar, S. K. Tripathy and L. A. SamuelsonAppl. Phys. Lett. 76(22) (2000), 3233-3235

Surface relief gratings (SRGs) were fabricated on composite films assembled by alternate electrostatic deposition of a polyelectrolyte, poly(dimethyldiallylammonium chloride), and an organic azo dye, congo red. The modulation of SRGs was found to increase with the thickness of the matrix films. Significant photochemical bleaching of the azo dye in the polymeric microenvironment as well as gradient-force-induced migration of the small azo dye contributes to the formation of the SRG structure. This finding demonstrates a facile method to fabricate SRGs for optical and information storage applications using commercially available azo dyes and polyelectrolytes. (C) 2000 American Institute of Physics. [S0003-6951(00)04922-6].

[25] Conformational State and Molecular Ionic Transformations of Polycytidyl Acid Immobilized in Multilayer Langmuir and Polyelectrolyte FilmsB. I. Sukhorukov, G. B. Sukhorukov, L. I. Shabarchina and M. M. MontrelBiofizika 45(1) (2000), 40-50

Multilayer films of complexes of polycytidylic acid with dioctadecyldimetylammonium were obtained by the Langmuir- Blodgett method (LB films), and complexes of poly(C) with polycations (poly-L-lysisne, polyethyleneimine, polyallylamine) were obtained by the method of alternate adsorption (polyionic assembly) from solutions of oppositely charged polyelectrolytes on the solid carrier (SA films). It was shown that poly(C) exists in SA films in a single-stranded state irrespective of whether in the starting solution it occurred in the single- stranded nonprotonated or double-stranded protonated conformation. Conversely, in the LB film poly(C) preferred to be in a double protonated conformation. UV-spectra of water- insoluble LB and SA films at different pH values of surrounding water medium were investigated. Proton titration curves of poly(C) immobilized in LB films were obtained. The analysis of the shape of titration curves showed that the molecular-ionic transformation of poly(C) in LB films is accompanied by both the conformational transition of the polynucleotide and the molecular rearrangement in the whole film. Poly(C) was found to transform from the double- to single-stranded state and vice versa in the <<deprotonation-protonation>> cycle of LB film due to cooperative release/binding of hydrogen ions by cytosine bases. In contrast, poly(C) <<protonation-deprotonation>> in SA films occurred without conformational transitions of the polynucleotide. As opposed to poly(C) in solution a rather big hysteresis of forward and back titration curves was found for both types of multilayer films, indicating molecular rearrangements in films. The reason for the structural transformations of poly(C) upon fabrication of LB or SA films and the mechanism of molecular ionic transformations of poly(C) in films art: discussed ill terms of a simple model of ion exchange. An assumption about the nature of structural transformations of LB and SA films during their protonation- deprotonation is put forward.

[26] Effect of Media Composition on Long-Term in-Vitro Stability of Barium Alginate and Polyacrylic-Acid Multilayer MicrocapsulesA. Gaumann, M. Laudes, B. Jacob, R. Pommersheim, C. Laue, W. Vogt and J. SchrezenmeirBiomaterials 21(18) (2000), 1911-1917

For a number of applications stability of microcapsules is a critical factor. Since the maintenance of polyelectrolyte complexes depends considerably on the ion composition we tested the physical properties of barium alginate capsules and searched for conditions to improve stability by a multilayer coating with polyethylenimine (PEI) and polyacrylic acid (PAA). Mechanical stability and diameters were determined in barium alginate capsules and compared with multilayer capsules. Multilayer coating resulted in smaller capsules than barium complexing alone. The difference was more pronounced when CaCl2 was used instead of NaCl during coating. Barium alginate capsules and application of CaCl2 during coating led to continuous pressure profiles, whereas NaCl resulted in bursting at a defined pressure, indicating the additional contribution to mechanical stability by the outer layers. After 7 d culture: mechanical stability of coated capsules decreased in RPMI and NaCl but was most pronounced in sodium citrate. The capsule diameter increased in sodium citrate, less pronounced in NaCl and was significantly different to RPMI and double distilled water. During long-term culture in RPMI, the diameter increased and mechanical stability decreased significantly, Multilayer coating improved mechanical stability which was impeded most in sodium citrate, to a lesser extent by NaCl and RPMI even after long-term exposure. (C) 2000 Elsevier Science Ltd, All rights reserved.

[27] Reagentless Biosensors Based on Self-Deposited Redox Polyelectrolyte-Oxidoreductases ArchitecturesA. Narvaez, G. Suarez, I. C. Popescu, I. Katakis and E. Dominguez


Biosensors and Bioelectronics 15(1-2) (2000), 43-52

Reagentless fructose and alcohol biosensors have been produced with a versatile enzyme immobilisation technique which mimics natural interactions and flexibility of living systems. The electrode architecture is built up on electrostatic interactions by the sequential adsorption of redox polyelectrolytes and redox enzymes giving rise to the efficient transformation of substrate fluxes into electrocatalytic currents. All investigated multilayer structures were self- deposited on 3-mercapto-1-propanesulfonic acid monolayers self- assembled on gold electrodes. Fructose dehydrogenase, horseradish peroxidase (HRP) and the couple HRP-alcohol oxidase were electrochemically connected with a cationic poly[(vinylpyridine)Os(bpy)(2)Cl] redox polymer (RP) interface in a layer-by-layer self-deposited architecture. The dependence of the distance on the electrochemical response of this interface was also studied showing a clear decrease in the Faradaic current when the distance to the electrode surface was increased. The sensitivities obtained for each biosensor were 19.3, 58.1 and 10.6 mA M-1 cm(-1) for fructose, H2O2 and methanol, respectively. The sensitivity values can be easily controlled by a rational deposition and manipulation of the charge in the catalytic layers. The electrostatic assembly of the electrochemical interface and the catalytic layers resulted in integrated biochemical systems in which mass transfer diffusion and heterogeneous catalytic and electron transfer steps are efficiently coupled and can be easily manipulated. (C) 2000 Elsevier Science S.A. All rights reserved.

[28] Construction of Multicomponent Catalytic Films Based on Avidin- Biotin Technology for the Electroenzymatic Oxidation of Molecular-HydrogenA. L. Delacey, M. Detcheverry, J. Moiroux and C. BourdillonBiotechn. Bioeng. 68(1) (2000), 1-10

Two methods based on the avidin-biotin technology were developed for the multimonolayer immobilization of Desulfovibrio gigas hydrogenase on glassy carbon or gold electrodes. In both methods the molecular structure of the modified interface was the result of a step-by-step process. The first method alternates monolayers of avidin and biotinylated hydrogenase, the mediator (methyl viologen) being free to diffuse in the structure. In the second method, the avidin monolayers were used to immobilize both the biotinylated enzyme and a long-chain biotinylated viologen derivative. The viologen head of this hydrophilic arm shuttles the electrons between the electrode and the enzyme. The modified electrodes were evaluated for the electroenzymatic oxidation of molecular hydrogen, which has interest for the development of enzymatic fuel cells. The parameters that affect the current density of mediated oxidation of H-2 at the modified electrodes was studied. The second structure, which has given typical catalytic currents of 25 mu A per cm(2) for 10 monolayers, was found clearly less efficient than the first structure (500 mu A per cm(2) for 10 monolayers). In both methods the catalytic currents increased linearly with the number of monolayers of hydrogenase immobilized, which indicates that the multilayer structures are spatially ordered. (C) 2000 John Wiley & Sons, Inc.

[29] Polyelectrolyte AdsorptionD. Andelman and J. F. JoannyC. R. Acad. Sci. Ser. IV, Phys. Astr. 1(9) (2000), 1153-1162

The problem of charged polymer chains (polyelectrolytes) as they adsorb on a planar surface is addressed theoretically. We review the basic mechanisms and theory underlying polyelectrolyte adsorption on a single surface in two situations: adsorption of a single charged chain, and adsorption from a bulk solution in theta solvent conditions. The behavior of flexible and semi-rigid chains is discussed separately and is expressed as function of the polymer and surface charges, ionic strength of the solution and polymer bulk concentration. We mainly review mean-field results and briefly comment about fluctuation effects. The phenomenon of polyelectrolyte adsorption on a planar surface as presented here is of relevance to the stabilization of colloidal suspensions. In this respect we also mention calculations of the inter-plate force between two planar surfaces in presence of polyelectrolyte. Finally, we comment on the problem of charge overcompensation and its implication to multi-layers formation of alternating positive and negative polyelectrolytes on planar surfaces and colloidal particles. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.

[30] Oxidation-Induced Variation in Polyelectrolyte Multilayers Prepared from Sulfonated Self-Dopable Poly(Alkoxythiophene)J. Lukkari, A. Viinikanoja, J. Paukkunen, M. Salomaki, M. Janhonen, T. Aaritalo and J. KankareJ. Chem. Soc., Chem. Commun. Iss 7 (2000), 571-572


Polyelectrolyte multilayers have been prepared using both the neutral and oxidised forms of a poly(alkoxythiophene) derivative with pendant sulfonate groups and it is shown that the oxidation state of the polymer affects multilayer formation.

[31] Self-Assembly of Freebase-Tetrapyridylporphyrins and Metalated- Tetrapyridylporphyrins to Modified Gold SurfacesC. V. K. Sharma, G. A. Broker, G. J. Szulczewski and R. D. RogersJ. Chem. Soc., Chem. Commun. Iss 12 (2000), 1023-1024

Freebase- and metallated-tetrapyridylporphyrins self-organize through multiple hydrogen bonding to carboxylic acid terminated self-assembled monolayers on gold surfaces, thereby producing surfaces with two additional functional sites, the porphyrin cavity and the terminal pyridyl groups.

[32] Nano-Size Stripes of Self-Assembled Bolaform AmphiphilesS. Gao, B. Zou, L. F. Chi, H. Fuchs, J. Q. Sun, X. Zhang and J. C. ShenJ. Chem. Soc., Chem. Commun. Iss 14 (2000), 1273-1274

Self-assembled nano-sized stripes are obtained spontaneously by electrostatic adsorption of bolaform amphiphiles onto mica sheets. The ordered stripes are separated from each other by about 10 nm, and the ordered region can extend over macroscopic areas.

[33] Fabrication of Hollow Zeolite SpheresX. D. Wang, W. L. Yang, Y. Tang, Y. J. Wang, S. K. Fu and Z. GaoJ. Chem. Soc., Chem. Commun. Iss 21 (2000), 2161-2162

Hollow spheres of zeolite have been fabricated through a layer- by-layer technique using polystyrene spheres as templates and nanozeolites as 'building blocks', followed by calcination.

[34] Multilayer Ultrathin Films of Molecular Titania Nanosheets Showing Highly Efficient UV-Light AbsorptionT. Sasaki, Y. Ebina, M. Watanabe and G. DecherJ. Chem. Soc., Chem. Commun. Iss 21 (2000), 2163-2164

Titania nanosheet crystallites have been self-assembled layer- by-layer with poly(dimethyldiallyl ammonium chloride) onto substrates to produce ultrathin nanostructured films which exhibit highly efficient optical absorption with a sharp peak at 266 nm.

[35] Template Synthesis of Polymer-Insulated Colloidal Gold Nanowires with Reactive EndsJ. S. Yu, J. Y. Kim, S. Lee, J. K. N. Mbindyo, B. R. Martin and T. E. MalloukJ. Chem. Soc., Chem. Commun. Iss 24 (2000), 2445-2446

Alternate adsorption of anionic and cationic polyelectrolytes creates smooth organic films on the walls of template-grown Au nanowires, which can be made chemically reactive on their ends by removal of a sacrificial Ag layer.

[36] Hollow Capsule Processing Through Colloidal Templating and Self- AssemblyF. CarusoChem. Eur. J. 6(3) (2000), 413-419

Hollow capsules of nanometer to micrometer dimensions constitute an important class of materials that are employed in diverse technological applications, ranging from the delivery of encapsulated products for cosmetic and medicinal


purposes to their use as lightweight composite materials and as fillers with low dielectric constant in electronic components. Hollow capsules comprising polymer, glass, metal, and ceramic are nowadays routinely produced by using various chemical and physicochemical methods. The current article focuses on a recent novel and versatile technique, based on a combination of colloidal templating and self-assembly processes, developed for synthesizing uniform hollow capsules of a broad range of materials. The strategy outlined readily affords control over the size, shape, composition, and wall thickness of the hollow capsules.

[37] Fabrication of Hollow Zeolite Fibers Through Layer-by-Layer Adsorption MethodY. J. Wang, Y. Tang, X. D. Wang, W. L. Yang and Z. GaoChem. Lett. Iss 11 (2000), 1344-1345

Hollow fibers with nanozeolite walls are firstly fabricated through layer-by-layer (LbL) technique, using carbon fibers as templates, coupled with removal of the templates by calcination. The thickness and the composition of the walls can be readily controlled by varying the number of the deposition cycles and the zeolite types used, respectively.

[38] In-Situ Nucleation and Growth of Gamma-FeOOH Nanocrystallites in Polymeric Supramolecular AssembliesA. K. Dutta, G. Jarero, L. Q. Zhang and P. StroeveChem. Mater. 12(1) (2000), 176-181

This paper reports the nucleation and growth of lepidocrocite (gamma-FeOOH) crystallites in supramolecular polymer multilayers. Organized, polymeric thin films were formed by the layer by layer deposition technique that consisted of adsorbing alternate layers of a polycation and a polyanion on a quartz substrate. Nucleation of nanoparticles was initiated by absorbing ferric nitrate in the thin film polymer matrix, followed by hydrolysis with ammonium hydroxide-1 Repeating the above process resulted in an increase in the density of the nanoparticles initially formed and further growth in the dimensions of the crystallites with the number of absorption and hydrolysis-cycles;Analysis of the UV-visible absorption spectra of the films revealed the formation of lepidocrocites, which was confirmed by FTIR and selected area electron diffraction (SAED) studies. An important feature of this work is that lepidocrocite (gamma-FeOOH) is formed instead of akaganeite (beta-FeOOH),which is generated when ferrous chloride is used as the starting material and is converted to iron oxyhydroxide through oxidative hydrolysis as reported in our previous work (Langmuir 1999, 15, 2176). It therefore seems likely that the initial starting material plays a key role in determining the structural and morphological characteristics of the iron oxyhydroxides although their chemical compositions are the same.

[39] Surface Sol-Gel Synthesis of Ultrathin Semiconductor-FilmsN. I. Kovtyukhova, E. V. Buzaneva, C. C. Waraksa, B. R. Martin and T. E. MalloukChem. Mater. 12(2) (2000), 383-389

Ultrathin films of ZnS, Mn-doped ZnS, ZnO, and SiO2 were grown on silicon substrates using surface sol-gel reactions, and the film growth process was characterized by ellipsometry, atomic force microscopy, X-ray photoelectron spectroscopy, UV-visible absorbance, and photoluminescence (PL) spectroscopy. The, Si substrates were pretreated by chemical oxidation, or by derivatization with 4- (dimethylmethoxy)silyl)butylamine. On the oxidized Si/SiOx surface, nanoparticulate films of ZnS and Mn-doped ZnS were grown by sequential immersion in aqueous metal acetate and sodium sulfide solutions. During the first four adsorption cycles, there was little film growth, but thereafter the amount of material deposited was linear with the number of adsorption cycles. This behavior is consistent with the formation of ZnS nuclei at low coverage, followed by particle growth in subsequent cycles. PL spectra are consistent with incorporation of Mn2+ into the ZnS nanoparticles. In contrast, the growth of SiO2 films from nonaqueous SiCl4 an the same Si/SiOx substrates was regular from the first adsorption cycle, indicating a high density of nucleation sites. On amine- derivatized substrates, ZnO thin films grew as relatively smooth islands, suggesting that the interaction of Zn2+ ions or primary ZnO clusters with the amine surface priming layer was sufficiently strong to prevent the formation of isotropic nanoparticles upon exposure to aqueous base.

[40] Nucleation and Growth of Lead Sulfide Nanocrystallites and Microcrystallites in Supramolecular Polymer AssembliesA. K. Dutta, T. T. Ho, L. Q. Zhang and P. StroeveChem. Mater. 12(4) (2000), 1042-1048


Multilayer thin film assemblies fabricated by the sequential adsorption of polyelectrolytes on a quartz substrate were used as a supramolecular reaction template to study the in situ nucleation and growth of PbS nano- and microparticles. Chemical reaction within the polymer film was initiated by absorbing pb(2+) from an aqueous solution of Pb(NO3)(2) followed by exposing the film to H2S gas. Electron microscopic examination of the films revealed that while nanoparticles are formed in films that were subject to one or two reaction cycles, large crystallites were formed when these films were exposed to a large number (10) of reaction cycles. In the latter case, a broad distribution of particle sizes is observed and may be attributed to Ostwald ripening. Detailed studies show the nucleation and growth of the PbS particles into crystallites of different shapes. UV-vis absorption studies reveal that the absorption spectral profiles of the films are dependent on the size of the PbS crystallites. The broadened absorption spectral profile observed for films subject to a large number of reaction cycles may be attributed to the superposition of the spectral profiles of the small clusters that tend to be blueshifted due to quantum confinement effects and the large clusters that are redshifted.

[41] Electrostatically Controlled Organization of Carboxylic-Acid Derivatized Colloidal Silver Particles on Amine-Terminated Self- Assembled MonolayersA. Gole, S. R. Sainkar and M. SastryChem. Mater. 12(5) (2000), 1234-1239

The formation of self-assembled monolayers (SAMs) of an aromatic bifunctional molecule, 4-aminothiophenol (4-ATP) on gold and the subsequent organization of carboxylic acid derivatized silver colloidal particles is described. Quartz crystal microgravimetry (QCM) measurements have been used to follow the formation of 4-ATP SAMs as well as electrostatic assembly of the colloidal silver particles on the SAM surface. It is shown that the electrostatic interaction between the negatively charged colloidal particle surface-bound carboxylic acid groups and the terminal amine groups in the SAM can be modulated by variation of the colloidal solution pH. This enables control over the surface coverage of the colloidal particles on the SAM surface with a maximum surface coverage of 18% being attained. The SAMs as well as the colloidal particle covered SAM films were further characterized with X-ray photoemission spectroscopy (XPS) and energy-dispersive analysis of X-rays (EDAX) measurements.

[42] Layer-by-Layer Assembled Films of HgTe Nanocrystals with Strong Infrared-EmissionA. L. Rogach, D. S. Koktysh, M. Harrison and N. A. KotovChem. Mater. 12(6) (2000), 1526

Layer-by-layer sequential adsorption (LBL) has been applied to the preparation of composite multilayer thin films of thiol- capped HgTe nanocrystals with strong IR luminescence. The films can be used as active coatings for novel optical sources for telecommunications.

[43] Layered Polyelectrolyte Films as Selective, Ultrathin Barriers for Anion TransportJ. J. Harris, J. L. Stair and M. L. BrueningChem. Mater. 12(7) (2000), 1941-1946

Synthesis of high-flux composite membranes requires methods for deposition of ultrathin, defect-free films on highly permeable supports. Layer-by-layer deposition of polyelectrolytes on porous alumina (0.02 mu m pore diameter) produces such membranes. Electron microscopy shows that five bilayers (<25 nm) of poly(allylamine hydrochloride) (PAH)/ poly(styrenesulfonate) (PSS) are sufficient to cover porous alumina and that underlying pores are not clogged during the deposition process. The selectivity of anion transport through these membranes increases with the number of bilayers until the substrate is fully covered. Five-bilayer PAH/PSS membranes have Cl-/SO42- and Cl-/Fe(CN)(6)(3-) selectivity values of 7 and 310, respectively. PAH/poly(acrylic acid) membranes show selectivity values similar to those of PAH/PSS membranes but with a 3-fold decrease in anion flux. Selectivity in both of these systems likely results from Donnan exclusion.

[44] Sol-Gel Processing of Ordered Multilayers to Produce Composite Films of Controlled ThicknessJ. H. Rouse, B. A. Macneill and G. S. FergusonChem. Mater. 12(8) (2000), 2502-2507

Sol-gel processing of a multilayered film formed by the alternate adsorption of poly(diallyldimethylammonium chloride) and a synthetic silicate sheet mineral, Laponite RD, resulted in an interpenetrating composite network.


Kinetic data indicate that the amount of material added due to sorption and gelation of tetraethyl orthosilicate (TEOS) reached a steady-state value within a day. Sol-gel growth occurred within the multilayer, with very little silicate being deposited at the surface. The resulting composite film showed the same order as an untreated multilayer, indicating that sorption and gelation did not disrupt the structural order of the multilayer. Curing the TEOS- treated films at 175 degrees C for 24 h to drive off excess water and complete the gelation process again resulted in an ordered composite structure. Cured films exposed to various levels of relative humidity demonstrated a dramatic decrease in swellability compared to an untreated multilayer.

[45] Ultrathin Composite Films Incorporating the Nanoporous Isopolyoxomolybdate Keplerate (NH4)(42)(Mo132O372(Ch3Coo)(30)(H2O)(72))D. G. Kurth, D. Volkmer, M. Ruttorf, B. Richter and A. MullerChem. Mater. 12(10) (2000), 2829

Ultrathin Composite Films Incorporating the Nanoporous Isopolyoxomolybdate ''Keplerate'' (NH4)(42)[Mo132O372- (CH3COO)(30)(H2O)(72)] The giant, nanoporous Keplerate (NH4)(42)- [Mo132O372(CH3COO)(30)(H2O)(72)] was incorporated into a permeable ultrathin film using a stepwise self-assembly strategy. Alternating adsorption of the Keplerate anions and PAH results in single layers with an apparent surface coverage of approximate to 50%. Such permeable composite coatings may lead into a practical approach to utilize nanoporous polyoxometalate clusters in sensors or heterogeneous catalysts.

[46] Hierarchical Assembly of Zeolite Nanoparticles into Ordered Macroporous Monoliths Using Core-Shell Building-BlocksK. H. Rhodes, S. A. Davis, F. Caruso, B. J. Zhang and S. MannChem. Mater. 12(10) (2000), 2832

Hierarchical Assembly of Zeolite Nanoparticles into Ordered Macroporous Monoliths Using Core-Shell Building Blocks Latex beads are used as a combined template and porogen in the fabrication of monolithic silica containing a hierarchy of pores. Prefabricated core/shell particles, prepared by the layer-by-layer assembly of zeolite (silicalite) nanoparticles onto spherical latex templates, are assembled into macroscopic close-packed structures. Calcination removes all organic components and causes densification of the inorganic structure producing a macroporous zeolite in which both the pore size and wall thickness can be varied.

[47] Metal-Films Prepared by Stepwise Assembly - 2 - Construction and Characterization of Colloidal Au and Ag MultilayersM. D. Musick, C. D. Keating, L. A. Lyon, S. L. Botsko, D. J. Pena, W. D. Holliway, T. M. Mcevoy, J. N. Richardson and M. J. NatanChem. Mater. 12(10) (2000), 2869-2881

This manuscript describes the stepwise, ligand-directed assembly, characterization, and prospective applications of three-dimensional Au and Ag nanoparticle, multlilayered films. Films were prepared by successive treatments of a Au nanoparticle monolayer with a bifunctional cross-linker and colloidal Au or Ag solutions. Changes in film electrical and optical properties are reported for a series of bifunctional cross-linkers of varying molecular lengths. Interestingly, these films exhibit Beer's law behavior despite the presence of strong interparticle optical coupling. Multilayer films with greater than six exposures to 2-mercaptoethylamine and Au colloid were highly conductive and resembled bulk Au in appearance. In contrast, films of similar particle coverage generated using a longer cross-linker (1,6-hexanedithiol) exhibited higher transmission in the near-infrared region and exhibited a reduced conductivity. Measurement of the multilayer morphology with atomic force microscopy, electrostatic force microscopy, and field emission scanning electron microscopy revealed a porous, discontinuous morphology composed of large, continuous regions of aggregated nanoparticles. This, in turn, results in a surface roughness contribution to surface plasmon scattering and surface-enhanced Raman scattering observed for Au, Au/Ag, and Ag colloid multilayers. Particulate multilayer films made using horseradish peroxidase as a cross-linker remained enzymatically active, even beneath three layers of colloidal Au. Multilayers could also be prepared on surfaces patterned by microcontact printing. These data show how Au colloid multilayers grown in solution are a viable alternative to evaporated metal films for a number of applications.

[48] Buildup of Polymer/Au Nanoparticle Multilayer Thin-Films Based on Hydrogen-Bonding


E. C. Hao and T. Q. LianChem. Mater. 12(11) (2000), 3392-3396

We report two new hydrogen-bonding-based routes for layer-by- layer fabrication of polymer/Au nanoparticle multilayer thin films. Two types of Au nanoparticles surface-modified with carboxyl groups or pyridine groups were prepared in nonaqueous solvents. In the first assembly route, we consecutively adsorbed poly(4-vinylpyridine) (PVP) and Au nanoparticles with carboxyl group tailored surfaces. In the second route, we alternatively deposited poly(acrylic acid) (PAA) and Au nanoparticles with pyridine group tailored surfaces. The multilayer buildup was monitored by UV-vis spectroscopy, which showed a linear increase of the film absorbance with the number of adsorbed Au layers. FTIR spectroscopy was used to verify hydrogen bonding between the pyridine and carboxyl groups, which is believed to be the driving force for the formation of polymer/Au multilayer thin films.

[49] Electron-Transfer Between Adjacent Layers in Self-Assembled FilmsV. B. P. Leite, M. Ferreira and O. N. OliveiraChem. Phys. Lett. 316(5-6) (2000), 343-348

A simple model of electron transfer is adapted to explain fluorescence quenching in self-assembled films of poly( p- phenylene vinylene) (PPV) alternating with poly(thiophene acetic acid) (PTAA). Quenching is caused by a photo-induced electron transfer between the excited PPV (donor, D) and the PTAA (acceptor, A). The electron-transfer process can be mediated by insertion of electronically inert spacing bilayers between the D and A layers, As the number of bilayers is increased, the fluorescence is gradually recovered which is explained theoretically by assuming that the electron-transfer rate can be described as k = Z exp(- beta r) where r is the distance between D and A. (C) 2000 Elsevier Science B.V. All rights reserved.

[50] Controlled Synthesis of Stable Poly(Vinyl Formamide-Co-Vinyl Amine)/Silica Hybrid Particles by Interfacial Post-Cross- Linking ReactionsI. Voigt, F. Simon, H. Komber, H. J. Jacobasch and S. SpangeColloid Polym. Sci. 278(1) (2000), 48-56

The chemical synthesis and the physicochemical properties of stable poly(vinyl formamide-co-vinyl amine)/silica hybrid particles are presented. Copolymers of poly(vinyl formamide) (PVFA) and poly(vinyl amine) (PVAm) and their protonated forms were adsorbed onto silica from aqueous solutions. The influences of the pH strength and the ion concentration of the aqueous solution as well as the copolymer composition (degree of hydrolyzation of PVFA). and the molecular mass on the adsorption process were investigated by electrokinetic measurements, potentiometric titration, and quantitative elemental analyses. Silica surface-charge neutralization is achieved at a pH strength above 10 for highly hydrolyzed (95%) PVFA polymers. Decreasing the amino content in the PVAm chain shifts successively both the point of zero charge and the isoelectric point to lower pH values. PVFA-co-PVAm layers onto silica are adsorbed weakly. To fix these layers irreversibly, cross-linking reactions with (4,4'-diisocyanate)diphenyl methane were carried out on the surface of solid PVFA-co-PVAm/ silica hybrid particles suspended in acetone. The cross-linking reaction, which is connected with the conversion of amino groups, is also a tool to control the surface charge of the PVFA-co-PVAm/silica hybrids. X-ray photoelectron spectroscopy and solid-state C-13 cross-polarization magic-angle spinning NMR spectroscopy were used to obtain information on the number of and the structure of the functionalized polyelectrolyte layers on silica. The success of cross-linking was also shown by the results of these spectroscopic methods.

[51] Synchronous Alternate Multilayered Adsorption of Poly(4-Vinyl-N- N-Butylpyridinium) Cations and Poly(Styrene Sulfonate) Anions on Polystyrene Colloidal SpheresT. Okubo and M. SudaColloid Polym. Sci. 278(4) (2000), 380-384

Alternate multiple adsorbed layers of up to six macrocations [poly(4-vinyl-N-n-butylpyridinium bromide)] and macroanions [sodium poly(styrene sulfonate)] are formed on monodispersed polystyrene colloidal spheres above the critical concentration of the macroions, m*. The m* value is the minimum number of macroions needed to reverse the sign of the zeta potential of the spheres in the first adsorption step. Alternate sign reversal in the zeta potential and expansive-contractive thickness changes are observed on the repeated and alternate addition of macrocations first and macroanions next. When the macroanions are added first, sign reversal in the zeta potential and reversible expansion and contraction do not occur. Breaking of the alternate multiple-type adsorption also occurs when equivalency in the number of dissociative groups of macrocations and macroanions is broken. Synchronous conformational changes of


macrocations and macroanions in the multiple-adsorbed layers occurs only when the conformational rigidities with the multiple electrostatic and hydrophobic attraction and/or repulsion between macrocations and macroanions are delicately balanced.

[52] From Langmuir Monolayers to NanocapsulesH. MöhwaldColloid Surf. A 171(1-3) (2000), 25-31

This report intends to draw a line from the controlled preparation and understanding of Langmuir monolayers to the fabrication of hollow capsules with exciting perspectives for basic science and applications. It is shown that methods used to characterize structure and transport properties of Langmuir and Langmuir-Blodgett films could be used to study polymeric ultrathin films. Since the latter are permeable to small molecules they could be used to prepare capsules after coating depolymerizable colloids. The inside of the capsule can be designed such that it is distinguished by inner walls and pH in the interior to perform a specific chemistry. As an application example selective precipitation of a dye molecule as a model for drug loading is presented. (C) 2000 Elsevier Science B.V. All rights reserved.

[53] Formation of Luminescent Spherical Core-Shell Particles by the Consecutive Adsorption of Polyelectrolyte and CdTe(S) Nanocrystals on Latex ColloidsA. S. Susha, F. Caruso, A. L. Rogach, G. B. Sukhorukov, A. Kornowski, H. Möhwald, M. Giersig, A. Eychmuller and H. WellerColloid Surf. A 163(1) (2000), 39-44

Functional core-shell particles were prepared by assembling a composite multilayer shell of charged polyelectrolytes and luminescent CdTe(S) nanocrystals (cadmium telluride with a certain content of sulfide) via their consecutive electrostatic adsorption from solution onto micron-sized latex particles. The formation of the composite shell has been confirmed by optical spectroscopy, confocal microscopy and high-resolution transmission electron microscopy. Variation of the size and surface chemistry of the semiconductor nanoparticles, the size and shape of the colloid templates, and the nature of the polyelectrolyte opens new avenues for the production of a variety of novel core-shell materials. (C) 2000 Elsevier Science B.V. All rights reserved.

[54] Lateral Lipid Diffusion in Phospholipid Monolayers Coupled to Polyelectrolyte FilmsM. Auch, B. Fischer and H. MöhwaldColloid Surf. A 164(1) (2000), 39-45

The lateral diffusion of lipid probes in lipid monolayers on polyelectrolyte support in different solvent environment was studied by a fringe pattern photobleaching experiment that enabled to measure diffusion coefficients D of over six orders of magnitude, In nonpolar solvents, as well as in air, electrostatic binding of ionic and also of zwitterionic lipids is so strong, that D < 10(-12) cm(2) s(-1) was observed. In polar solvents (e.g. methanol), the interaction is reduced for zwitterionic lipids, enabling D > 10(-7) cm(2) s(-1). In water, the coupling is similarly reduced for zwitterionic, not for ionic lipids. In the case of a weak interaction with the polymer, one encounters a temperature dependence for the monolayer of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) as expected for a system with a fluid/gel phase transition. (C) 2000 Elsevier Science B.V. All rights reserved.

[55] Polyelectrolyte Adsorption Processes Characterized in-Situ Using the Quartz-Crystal Microbalance Technique - Alternate Adsorption Properties in Ultrathin Polymer-FilmsA. Baba, F. Kaneko and R. C. AdvinculaColloid Surf. A 173(1-3) (2000), 39-49

The alternate adsorption processes of polyelectrolytes from solution have been investigated in situ using a functionalized (gold electrode) quartz substrate via the quartz crystal microbalance (QCM) technique. The deposition process involved the alternate layer by layer electrostatic (Coulombic) interaction between oppositely charged adsorbing polyelectrolytes resulting in ultrathin multilayer films. Three kinds of polyelectrolyte combinations were used: poly(diallyldimethylammonium chloride) (PDADMAC), poly(ethylenimine) (PEI) and poly(allylamine hydrochloride) (PAH) as the cationic polymers and poly(sodium-4- styrensulfonate) (PSS) as the anionic polymer for


polycation/ polyanion combinations. The electrical behavior of the piezoelectric 'quartz crystal' was sensitive to the adsorption properties of the polyelectrolytes, thus allowing dose observation of the time-dependent adsorption processes. The adsorption relationship was explored for different polyelectrolyte pair-combinations, alternate solution concentration and the presence of rinsing and drying steps. The results showed that the amount of frequency change is mostly dependent on the immediate subphase environment of the crystal surface, i.e. aqueous environment versus air in relation to the classic Sauerbrey equation. (C) 2000 Elsevier Science B.V. All rights reserved.

[56] Influence of the Ionic-Strength on the Structure of Polyelectrolyte Films at the Solid/Liquid InterfaceR. Steitz, V. Leiner, R. Siebrecht and R. VonklitzingColloid Surf. A 163(1) (2000), 63-70

The structure of polyelectrolyte multilayers built up by alternate adsorption of polyanions and polycations is investigated by X-ray reflectivity at the solid/air and neutron reflectivity at the solid/liquid interface. The experiments provide detailed information about the density gradient of polyelectrolyte chains across the film and show the influence of the water content of the film on the internal structure. The polyelectrolyte density is determined by the adsorption conditions (e.g. amount of NaCl) and cannot be changed by addition of salt after adsorption. After drying the film thickness is reduced by 30%. (C) 2000 Elsevier Science B.V. All rights reserved.

[57] Electrostatic Adsorption of Polystyrene Particles with Different Surface-Charges Onto the Surface of an Ultrathin Polymer FilmT. Serizawa, S. Kamimura and M. AkashiColloid Surf. A 164(2-3) (2000), 237-245

The adsorption of polystyrene particles with different surface charges from aqueous dispersions onto the surfaces of cationic ultrathin polymer films was quantified using a quartz crystal microbalance (QCM) technique. The polymer films were prepared by the alternate adsorption technique from poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) in the presence or absence of NaCl onto the QCM substrate. Particle adsorption, as a result of electrostatic interaction, onto the outermost PAH surface was observed by QCM. The adsorption behavior of two differently charged particles was examined and revealed greater adsorption of particles with a relatively larger surface charge. The dependence of adsorption of all the particles against an outermost PAH thickness in a polymer precursor film was described by a sigmoid curve, indicating that a critical charge on/in the him is required for adsorption. SEM observations showed monolayer adsorption without three-dimensional aggregation. (C) 2000 Elsevier Science B.V. All rights reserved.

[58] Assembly of Beta-Glucosidase Multilayers on Spherical Colloidal Particles and Their Use as Active CatalystsF. Caruso, H. Fiedler and K. HaageColloid Surf. A 169(1-3) (2000), 287-293

beta-glucosidase (beta-GLS) layers of the enzyme, each separated by oppositely charged polyelectrolyte (poly(styrenesulfonate), PSS), were deposited onto polystyrene (PS) latex particles using the layer-by-layer adsorption technique. Electrophoretic mobility (EPM) and single-particle light scattering (SPLS) measurements revealed regular and stepwise assembly of beta-GLS/PSS multilayers on the colloidal particles. Alternating positive and negative zeta-potentials were observed for beta-GLS and PSS deposition, respectively. An average thickness of 3.5 +/- 0.6 nm was calculated for each beta-GLS/PSS layer pair from SPLS data. The immobilized catalyst (in the form of an enzyme multilayer film on particles) proved to be active in the glucosidation of dodecanol, yielding dodecyl-beta-D-glucopyranoside. The product yield increased with increasing enzyme layer number for beta- GLS multilayer-coated PS particles when the outermost layer was polyelectrolyte. (C) 2000 Elsevier Science B.V. All rights reserved.

[59] Assembly and Structural Study of the Films of Immunoglobulin-M on Solid SubstratesR. L. Kayushina, A. L. Tolstikhina, N. D. Stepina, V. V. Belyaev, V. A. Lapuk and E. Y. VarlamovaCrystallogr. Rep. 45(6) (2000), 1001-1006

Immunoglobulin M (IgM) was immobilized from a solution by the method of charge self-assembly on solid substrates (ordered polyelectrolytes and as-cleaved mica). The process of film formation and the structural organization was controlled and studied by the methods of atomic-force microscopy and X-ray reflectometry. It was shown that


adsorption from rather concentrated (0.680-0.068 mg/ml) IgM solutions gave rise to formation of 100- to 150-Angstrom -thick continuous protein layers. At lower concentrations (0.006 mg/ml), no continuous protein films were formed. The substrates of mica-type atomically smooth surfaces provide a higher image resolution, which, in turn, allows the observation of isolated IgM molecules and their aggregates. In the image plane, the molecules have rounded contours 300-500 Angstrom in diameter and 40-60 Angstrom in height. (C) 2000 MAIK ''Nauka/ Interperiodica''.

[60] Layer-by-Layer Electrostatic Deposition of Biomolecules on Surfaces for Molecular Recognition, Redox Mediation and Signal GenerationE. J. Calvo, F. Battaglini, C. Danilowicz, A. Wolosiuk and M. OteroFARADAY DISCUSS Iss 116 (2000), 47-65

Layer-by-layer supramolecular structures composed of alternate layers of negatively charged enzymes and cationic redox polyelectrolyte have been assembled. Glucose oxidase (GOx), lactate oxidase (LOx) and soybean peroxidase (SBP) have been electrically wired to the underlying electrode by means of poly(allylamine) with [Os(bpy)(2)ClPyCOH](+) covalently attached (PAA-Os) in organized structures with high spatial resolution. Biotinylated glucose oxidase has also been used to assemble step-by-step on antibiotin goat immunoglobulin (IgG) layers and the enzyme was electrically wired by PAA-Os. These spatially organized multilayers with mono- and bienzymatic schemes can work efficiently in molecular recognition, redox mediation and generation of an electrical signal. The concentration of redox mediator integrated into the multilayers, obtained from the voltammetric charge and an estimation of the layer thickness, exceeds by 100-fold the amount of deposited enzyme assessed by quartz crystal microbalance. Differences in GOx electrical wiring efficiency have been detected with the different assembling strategies. The surface concentration of electrically wired enzyme represents a small proportion of all the enzyme molecules present in the multilayers which can be oxidized by the soluble mediator [Os(bpy)(2)Cl PyCOOH]Cl. This proportion, as well as the rate of FADH(2) oxidation by PAA-Os, increases with the number of electrically wired enzyme layers and with the spatial accessibility of the Os moiety to the enzyme active center.

[61] Applications of Polyion Films Containing Biomolecules to Sensing ToxicityJ. F. Rusling, L. P. Zhou, B. Munge, J. Yang, C. Estavillo and J. B. SchenkmanFARADAY DISCUSS Iss 116 (2000), 77-87

This paper describes several applications of polyion- biomolecule films on electrodes related to future development of in vitro chemical toxicity sensors. In the first example, composite films of DNA and ionomers cast onto pyrolytic graphite (PG) electrodes are shown to be useful for detecting DNA damage during incubation with the carcinogen styrene oxide at pH 5.5. Single electrodes can be used to estimate relative damage rates by derivative square wave voltammetry. Films containing the ionomer Nafion gave better reproducibility than another ionomer, Eastman AQ38. In the second example, films containing redox proteins myoglobin (Mb) and cytochrome (cyt) P450(cam) were constructed in alternate layers with polyions including DNA on rough PG electrodes. Films with reversible protein Fe-III/Fe-II electrochemistry with up to 7 electroactive layers were made. Amounts of electroactive protein on rough PG that were 7 to 17-fold larger than in similar films on smooth gold were achieved because many more layers were electroactive. Films of Mb/DNA also showed oxidation peaks after short incubations with styrene oxide that may be attributable to DNA damage. Results are relevant to the future design of enzyme-DNA films which convert pollutants and drugs to reactive metabolites, followed by electrochemical detection of the resulting DNA damage.

[62] Ultrathin, Layered Polyamide and Polyimide Coatings on AluminumJ. H. Dai, D. M. Sullivan and M. L. BrueningIND ENG CHEM RES 39(10) (2000), 3528-3535

Ultrathin, passivating films are attractive for protecting metal surfaces without completely masking substrate properties. Alternating polyelectrolyte deposition of layered poly(acrylic acid)/ poly(allylamine hydrochloride) (PAA/PAH) films on Al produces ultrathin coatings that protect Al from Cl--induced corrosion. Although the resistance of these films is minimal, they form a passivating layer on the surface oxide and increase oxide resistance by 2-3 orders of magnitude. Heating of PAA/PAH yields cross-linked polyamides that have film resistances of about 5 M Omega cm(2), even when the film is only 10-nm thick. Although the resistance of these films is high, reductions in corrosion current due to cross-linked films are still primarily due to passivation of the surface oxide as oxide resistance is larger than film resistance. Layer-by-layer covalent deposition of Gantrez/poly(allylamine) films yields ultrathin amic acid- linked layers that can be imidized by heating. Impedances of Al electrodes coated with Gantrez/poly(allylamine) films depend on the number of deposited bilayers and increase by an order of magnitude


after imidization. These results suggest that increases in film resistance play a role in oxide passivation by this system.

[63] Layer-by-Layer Deposition of J-Aggregates and Polyelectrolytes for Electroluminescence Applications - A Spectroscopic StudyS. Kirstein, S. Bourbon, M. Y. Gao and U. DerossiIsr. J. Chem. 40(2) (2000), 129-138

The self-assembly method of layer-by-layer deposition of oppositely charged polyelectrolytes is used to insert J- aggregates of the dye tetrachloro-diethyl-disulfobutyl- benzimido-carbocyanine (TDBC) into thin polymeric films. The J- aggregates are characterized by a narrow absorption- and fluorescence band with its maximum at 590 nm, which is redshifted with respect to the monomeric transition at 515 nm. The dyes are either coadsorbed with the polyelectrolytes poly(allylamine hydrochloride (PAH) and poly(styrene sulfonate) (PSS), or alternately deposited with the precursor of poly(phenylene vinylene) (pre-PPV). The optical properties of the aggregates are nor changed significantly by the deposition process. The pre-PPV/TDBC films are heated under vacuum to convert the PPV to its conjugated form. The resulting films can be used fur the fabrication of light-emitting devices. The optical properties such as fluorescence and electroluminescence are dominated by the J-aggregates. The excitation energy of PPV is transferred to the dye aggregates with an efficiency of 100%. The electroluminescence is not very stable and shows a very slow turn-on time. However, the combination of self- assembled PPV/TDBC layers with a spin-coated film of PPV results in stable electroluminescence emission under ambient conditions. In this case, light is emitted from both species, the PPV and the J-aggregates, whereas the ratio of the two intensities strongly depends on temperature.

[64] Stepwise Stereocomplex Assembly of Stereoregular Poly(Methyl Methacrylate)S on a SubstrateT. Serizawa, K. Hamada, T. Kitayama, N. Fujimoto, K. Hatada and M. AkashiJ. Am. Chem. Soc. 122(9) (2000), 1891-1899

Isotactic (it-) and syndiotactic (st-) poly(methyl methacrylate)s (PMMAs) were synthesized by anionic polymerization in toluene at -78 degrees C with t-C4H9MgBr and t-C4H9Li/(C2H5)3Al, respectively, as initiators. Polymers were assembled by the stepwise immersion of a 9-MHz quartz-crystal microbalance (QCM) as a substrate into organic solutions at ambient temperature. Quantitative QCM analysis revealed that acetonitrile was the best solvent for assembly on the substrate compared to acetone and N,N-dimethylformamide (DMF). The analysis also showed linear growth of the assembly except during the initial two steps (possibly due to direct influence of the gold QCM substrate), indicating that the amount of assembly can be easily regulated at each step. A 5 min immersion of the QCM into each PMMA solution was enough to obtain stepwise assembly. The ratios of st-/it-PMMA assembled, the static contact angle of the assembly at each step, and its reflection absorption spectrum (RAS) strongly implied the stepwise formation of a stereocomplex between it- and st-PMMAs in the assembly. The amount of stereocomplex assembled was significantly affected by the addition of water to the organic solutions, the PMMA concentration, and its molecular weight, as well as the solvent species. Atomic force microscopic (AFM) examination of the assembly revealed a smooth surface. The assembly was formed at the step from the physically adsorbed it- PMMA to st-PMMA. A possible assembling mechanism was also proposed.

[65] Adsorption and Desorption Behavior of an Anionic Pyrene Chromophore in Sequentially Deposited Polyelectrolyte-Dye Thin- FilmsC. Tedeschi, F. Caruso, H. Möhwald and S. KirsteinJ. Am. Chem. Soc. 122(24) (2000), 5841-5848

Alternating thin films of the anionic dye pyrenetetrasulfonic acid (4-PSA) and poly(allylamine hydrochloride) (PAH) were formed by the sequential deposition of 4-PSA and PAH from aqueous solution onto solid substrates. Film growth was followed by absorption spectroscopy, and the resulting polyelectrolyte dye multilayer assemblies were characterized by using fluorescence spectroscopy, X-ray reflectivity, and atomic force microscopy (AFM) measurements. 4-PSA was successfully deposited in alternation with PAH when the ionic strength of the BAH solution was greater than 0.1 M. At each PAH adsorption step a given amount of previously adsorbed 4-PSA was extracted. The amount of dye released depended on the film thickness and the salt concentration in the PAH solution from which PAH was subsequently adsorbed. However, the total amount of dye remaining in the film after PAH deposition was essentially independent of the salt content in the PAH solution. Both X-ray reflectivity and AFM measurements revealed a high roughness of the 4-PSA/PAH multilayer films (ca. 20 Angstrom). To gain a better understanding of the parameters that control dye adsorption and extraction, dye adsorption was also investigated by immersion of preformed PAH and poly(styrene sulfonate) (PSS) multilayer films of various thickness into 4-PSA solutions. The amount of 4-PSA absorbed by the films increased with film thickness, and saturated at a thickness


above about 20 nm. For these films, subsequent adsorption of a PAH layer extracted most of the dye, except for a small amount approximately equal to that present in one 4-PSA/PAH bilayer prepared by the alternate adsorption process. These observations indicate that the dye molecules are adsorbed to a finite depth of about 20 nm, and after deposition of the oppositely charged PAH, a small amount that is independent of film thickness remains. The presence of this remaining 4-PSA is necessary to complex and bind the next PAH layer, hence allowing continued multilayer film growth. It was also found that the 4-PSA adsorption/ desorption process depended on the drying process that was employed during the formation of the PSS/PAH multilayer films. The amount of dye as well as the penetration depth was reduced when the film was dried between deposition of each layer, and minor changes in the film structure were observed by X-ray reflectivity measurements.

[66] Influence of Polyelectrolyte Multilayer Films on Calcium- Phosphate NucleationP. A. Ngankam, P. Lavalle, J. C. Voegel, L. Szyk, G. Decher, P. Schaaf and F. J. G. CuisinierJ. Am. Chem. Soc. 122(37) (2000), 8998-9004

The nucleation of calcium phosphate crystals from a weakly supersaturated calcium phosphate solution on the surface of polyelectrolyte multilayers was investigated in dependence on the chemical nature of the outermost layer. Scanning angle reflectometry was used to follow in situ the initial stages of the nucleation kinetics. The multilayers were constructed by alternate adsorption of poly(styrene sulfonate) (PSS) and poly(allylamine) (PAH), leading to oppositely charged surfaces. It was verified that films terminating with either PSS or PAH exhibited a negative or positive 5-potential, respectively. Surprisingly, both types. of surface layers induced a nucleation process for supersaturations smaller than the one observed on the bare silica surface. According to the literature, such an effect should only be expected on a negatively charged surface. Infrared spectroscopy showed that the nucleated crystals are hydroxyapatite (OHAP) or octacalcium phosphate (OCP) but not dicalcium phosphate dihydrate (DCDP) which is found on bare silica surfaces. On both PSS and PAH surfaces, the nucleation processes started only after a given induction time. The evolution of the induction times with different supersaturations was analyzed within the framework of the classical nucleation theory. The effective surface free energies of the formed crystals were estimated to be on the order of 32 mJ.m(-2) on a multilayer terminating with PSS and to be about 37 mJ.m(-2) on a multilayer terminating with PAH. A mechanism for the enhanced nucleating effect of such polyelectrolyte surfaces is proposed.

[67] Layered, Erasable, Ultrathin Polymer-FilmsS. A. Sukhishvili and S. GranickJ. Am. Chem. Soc. 122(39) (2000), 9550-9551

[68] Photoelectrochemistry with Integrated Photosensitizer-Electron Acceptor and Au-Nanoparticle ArraysM. Lahav, V. Helegshabtai, J. Wasserman, E. Katz, I. Willner, H. Durr, Y. Z. Hu and S. H. BossmannJ. Am. Chem. Soc. 122(46) (2000), 11480-11487

Photosensitizer/electron acceptor molecular cross-linked Au- nanoparticle arrays are assembled on indium-doped tin oxide (ITO) electrodes by a layer-by-layer deposition process. A Ru(II)-tris-(2, 2'-bipyridine)cyclobis(paraquat-p-phenylene) catenane (1) or Zn(II)-protoporphyrin IX-bis(N-methyl-N'- undecanoate-4,4'-bipyridinium) (2) are used as molecular cross- linkers for the generation of Au-nanoparticle (13 +/- 1 nm) arrays of a controlled number of layers. The Au-nanoparticle arrays are characterized by absorbance spectroscopy and by electrochemical means. The electrodes functionalized with 1- or 2-cross-linked Au-nanoparticle arrays are used in photoelectrochemical experiments. The resulting action spectra of the photocurrents follow the absorbance spectra of the respective chromophores. Mechanistic studies indicate that the photocurrents originate from intramolecular electron-transfer quenching of the photoexcited state of the photosensitizer by the electron acceptor units, leading to the formation of intermediate redox species. The oxidized photoproduct oxidizes the sacrificial electron donor, Na(2)EDTA, whereas the reduced bipyridinium radical cations transfer the electrons to the bulk electrode support.

[69] Electroluminescence of Different Colors from Polycation/CdTe Nanocrystal Self-Assembled FilmsM. Y. Gao, C. Lesser, S. Kirstein, H. Möhwald, A. L. Rogach and H. WellerJ. Appl. Phys. 87(5) (2000), 2297-2302

Water soluble thiol capped CdTe nanocrystals are assembled into ultrathin films in combination with poly(diallyldimethylammonium chloride) (PDDA) by the self- assembly method of layer-by-layer adsorption of oppositely charged polyelectrolytes. Electroluminescent devices, which produce different color emissions, are


fabricated by sandwiching CdTe/PDDA films between indium-tin-oxide (ITO) and aluminum electrodes using CdTe nanocrystals of different sizes. It is shown that the electroluminescence (EL) spectra of the CdTe/polymer films are nearly identical to the photoluminescence spectra of the corresponding CdTe nanocrystals in aqueous solutions. The devices produce room- light visible light output with an external quantum efficiency up to 0.1%. Light emission is observed at current densities of 10 mA/cm(2) and at low onset voltages of 2.5-3.5 V, which depends on the thickness of the film indicating field-dependent current injection. A variation of the EL efficiency with the size of the CdTe particles is observed and explained by the size dependent shift of the CdTe energy levels with respect to the work function of the electron injecting Al electrode. This is confirmed by the behavior of two-layer devices prepared from two differently sized CdTe particles being spatially separated, i.e., one size CdTe near ITO and the other size CdTe near Al by using the self-assembly method. (C) 2000 American Institute of Physics. [S0021-8979(00)06404-5].

[70] Self-Assembled Multilayer Films Based on Diazoresins Studied by Atomic-Force Microscopy/Friction Force MicroscopyL. Huang, G. B. Luo, X. S. Zhao, J. Y. Chen and W. X. CaoJ. Appl. Polym. Sci. 78(3) (2000), 631-638

The layer-by-layer self-assembled NDR-PSS (nitro-containing diazoresin-polysodium p-styrenesulfonate) films were fabricated. The crosslinking structure formed from the conversion of ionic bond to covalent bond after UV irradiation, confirmed by small angle X-ray diffraction. The roughness and microtribological properties of NDR-PSS films were investigated by atomic force microscopy/friction force microscopy. The ordered multilayer films after photoreaction are better in microtribological performance than that of the monolayer film. (C) 2000 John Wiley & Sons, Inc.

[71] Probing Nanoscale Photooxidation in Organic Films Using Spatial Hole-Burning Near-Field Scanning Optical MicroscopyG. M. Credo, G. M. Lowman, J. A. Dearo, P. J. Carson, D. L. Winn and S. K. BurattoJ. Chem. Phys. 112(18) (2000), 7864-7872

Spatial hole burning near-field scanning optical microscopy (SHB-NSOM) is used to locally photopattern three species of organic thin films, poly(2-methoxy, 5-(2'-ethyl hexyloxy)-p- phenylene vinylene) (MEH-PPV), tris-8-hydroxyquinoline aluminum (Alq(3)) and dye-functionalized polyelectrolyte self-assembled layers, on a 100 nm length scale. In SHB-NSOM the film is illuminated with light from a stationary NSOM tip to induce photo-oxidation. The reduction in the fluorescence yield resulting from this exposure is then mapped using fluorescence NSOM (FL-NSOM). We have examined the localized photo-oxidation as a function of time, position, and environment free from the limits of far-field spatial averaging. In all of the thin film materials studied we find that the long-time diameter of the dark spot is much larger than the tip diameter and is a signature of energy migration. Characteristic lengths of the energy migration are extracted from this data by a simple diffusion model and are found to be of the order of a few hundred nanometers for each of the films studied. (C) 2000 American Institute of Physics. [S0021-9606(00)71116-0].

[72] Facile Construction of an Ultra-Thin (60)Fullerene Layer from (60)Fullerene-Homooxacalix(3)Arene Complexes on a Gold SurfaceT. Hatano, A. Ikeda, T. Akiyama, S. Yamada, M. Sano, Y. Kanekiyo and S. ShinkaiJ. Chem. Soc., Perkin Trans. 2 5(MAY) (2000), 909-912

A hexacationic homooxacalix[3]arene-[60]fullerene 2:1 complex can be deposited on an anion-coated gold surface as a monolayer (or at least as a monolayer-like ultra-thin film); as expected, this membrane efficiently shows a redox response in cyclic voltammetry and a photoelectrochemical response under visible light irradiation.

[73] Investigation of Structure and Growth of Self-Assembled Polyelectrolyte Layers by X-Ray and Neutron-Scattering Under Grazing AnglesA. Plech, T. Salditt, C. Munster and J. PeislJ. Colloid Interface Sci. 223(1) (2000), 74-82

The structure of self-assembled polyelectrolyte thin films on float glass has been investigated by interface sensitive X-ray and neutron scattering methods. Special emphazis was given to the adsorption process of poly (ethylene imine) and polystyrole sulfonate as an important model system which is often used as a basis for subsequent multilayer


buildup. From complementary X- ray and neutron reflectivity data, the vertical film density profile was derived for various growth parameters, including kinetic effects of different adsorption times. In addition to specular reflectivity, we have for the first time employed nonspecular X-ray scattering to study lateral structure parameters in self-assembled polyelectrolyte films. Furthermore, the technique of time-resolved in situ X-ray reflectivity during film growth has been demonstrated and is discussed in view of its future potential. (C) 2000 Academic Press.

[74] Phosphatidylserine/Cholesteral Bilayers Supported on a Polycation/Alkylthiol Layer PairL. Q. Zhang, C. A. Booth and P. StroeveJ. Colloid Interface Sci. 228(1) (2000), 82-89

1-Stearoyl-2-oleoyl phosphatidylserine (SOPS)/cholesterol bilayers, supported on a polycation/alkylthiol layer pair on a gold surface, were investigated by surface plasmon resonance (SPR) and fluorescence recovery after photobleaching. The substrate was formed by electrostatic adsorbance of a hydrated poly(diallyldimethylammonium chloride) (PDDA) layer on the negatively charged surface of a self-assembled monolayer of 11- mercaptoundecanoic acid (MUA) on gold. Lipid membranes with different SOPS/cholesterol compositions were deposited on the PDDA/MUA layer pair by vesicle fusion. When the cholesterol content was below 20%, single bilayers were deposited. Fluorescence recovery after the bleaching experiments revealed that the SOPS/cholesterol bilayers were mobile at room temperature; lateral diffusion coefficients of a fluorescence probe were approximately 1 x 10(-9) cm(2)/s. The kinetics of the addition of the ion-channel-forming peptide gramicidin to the supported bilayers was detected by SPR. (C) 2000 Academic Press.

[75] Electroactive Films of Alternately Layered Polycations and Iron- Sulfur Protein Putidaredoxin on GoldZ. Q. Lu, Y. Lvov, I. Jansson, J. B. Schenkman and J. F. RuslingJ. Colloid Interface Sci. 224(1) (2000), 162-168

Layered, electrochemically active films of bacterial iron- sulfur protein putidaredoxin (Pdx) and poly(dimethyldiallyammonium) (PDDA) polycations were constructed on gold electrodes coated with mercaptopropane sulfonate (MPS) and on quartz slides. Second-derivative UV-vis spectra suggested similar structures of Pdx in films and solutions at pH 7. Direct electrochemistry was achieved between Pdx and gold electrodes in these films, with significantly better electrochemical reversibility than in cast Nafion-lipid- Pdx films. A formal potential dispersion model gave a good fit to square wave voltammograms by regression analysis and was used to estimate an average apparent rate constant of 4.5 s(- 1). Reduced Pdx in the polyion films did not react with its natural redox partner cytochrome P450(cam) because of unfavorable thermodynamics in the film environment. (C) 2000 Academic Press.

[76] Assembly of Alternated Multivalent Ion/Polyelectrolyte Layers on Colloidal Particles - Stability of the Multilayers and Encapsulation of Macromolecules into Polyelectrolyte CapsulesI. L. Radtchenko, G. B. Sukhorukov, S. Leporatti, G. B. Khomutov, E. Donath and H. MöhwaldJ. Colloid Interface Sci. 230(2) (2000), 272-280

Alternating adsorption of multivalent ions and oppositely charged polyelectrolytes on colloid particles has been investigated. Multilayer films composed of Tb3+/polysterene sulfonate (PSS) and 4-pyrene sulfate/polyallylamine (PAH) were successfully assembled on polysterene sulfonate (PS) and melamine formaldehyde (MF) latex particles. The amount of assembled material was estimated by fluorescence and the linear growth of the film versus the number of layers was demonstrated. These multilayers are not stable and can be decomposed by salt and temperature, Dissolution of MF particles leads to formation of hollow capsules consisting of multivalent ion/polyelectrolyte multilayers. Comparative analysis of the capsules was done by confocal and scanning force microscopy. Complex hollow spheres consisting of Tb3+/PSS or 4-PS/PAH as an inner shell and stable PSS/PAH as an outer shell were produced. Due to selective permeability of the outer shell after degradation of the inner shell the multivalent ions are released out of the capsule while the polyelectrolytes fill the capsule interior. This is indicative of swelling of the capsule by osmotic pressure. The filled capsules were studied by confocal and scanning electron microscopy. Possibilities of encapsulating macromolecules in defined amounts per capsule are discussed. (C) 2000 Academic Press.

[77] Comparative-Studies on Electrochemical-Behavior and Electrocatalytic Properties of Heteropolyanion-Containing Multilayer Films Prepared by 2 Methods


L. Cheng and S. DongJ. Electroanal. Chem. 481(2) (2000), 168-176

Two modification methods for multilayer formation, i.e. immersion growth and electrochemical growth, were studied comparatively for their influence on the electrochemical behavior and the electrocatalytic properties of the thus- fabricated SiMo11V-containing multilayer films. Electrochemical growth was proven to be a more suitable method than immersion growth in preparing uniform ultrathin multilayer self- assemblies with good functions. We investigated the effects of scan rate and pH on the electrochemical behavior of the monolayer and multilayer films. We also compared the electrocatalytic effects on the reduction of BrO3- and HNO2 by the multilayer films prepared by the two methods. Moreover, the influence of multilayer thickness and the identity of the outermost layer on the electrocatalytic properties were studied. Much higher catalytic currents appeared on the thicker multilayer films than those on the thinner ones. On the other hand, the catalytic currents became smaller when the multilayer films with SiMo11V as the outermost layer were covered with an additional quarternized poly(4-vinylpyridine) layer partially complexed with osmium bis(2,2'-bypyridine) chloride (QPVP-Os layer). These influences were believed to be due to the different quantities of electrocatalyst loaded in the multilayer films and the blocking effect of the QPVP-Os outermost layer. (C) 2000 Elsevier Science S.A. All rights reserved.

[78] An Enlarged bis-Bipyridinium Cyclophane-Au Nanoparticle Superstructure for Selective Electrochemical Sensing ApplicationsM. Lahav, A. N. Shipway, I. Willner, M. B. Nielsen and J. F. StoddartJ. Electroanal. Chem. 482(2) (2000), 217-221

Highly stable electrostatically-linked superstructures of 13 nn Au-colloids have been constructed by the use of the tetracationic cyclophanes cyclobis(paraquat-p-phenylene) and cyclobis(paraquat-p-biphenylene). These architectures have been characterized by optical and electrochemical means and exhibit sensing capabilities that are shown to depend on the crosslinking cyclophane. While superstructures linked by cyclobis(paraquat-p-phenylene) sense hydroquinone derivatives and not ferrocene derivatives, those linked by the larger receptor cyclobis(paraquat-p-biphenylene) sense only the ferrocene derivatives. This high degree of selectivity is based on the topological and supramolecular fit of the analyte in the cavity of the receptor. Arrays containing both cyclophanes are shown to exhibit sensing characteristics that are dependent on the position of each cyclophane in the superstructure, possibly as a consequence of the limited porosity of the composite. (C) 2000 Elsevier Science S.A. All rights reserved.

[79] Electrochemical-Behavior and Electrocatalytic Properties of Ultrathin Films Containing Silicotungstic Heteropolyanion Siw12O404-L. Cheng and S. J. DongJ. Electrochem. Soc. 147(2) (2000), 606-612

We describe here a controlled fabrication of ultrathin monolayer and multilayer films consisting of silicotungstic heteropolyanion SiW12O404- and a cationic polymer of quaternized poly(4-vinylpyridine) partially complexed with osmium bis(2,2'-bipyridine) on Au electrodes previously self- assembled with cysteamine monolayers based on layer-by-layer electrostatic interaction. The thus-forming monolayer and multilayer chemically modified electrodes are investigated by cyclic voltammetry on their electrochemical behavior and electrocatalytic properties. The composite ultrathin films exhibit remarkable electrocatalytic effects on the reduction of BrO3-, H2O2, and HNO2. The electrocatalytic effects on HNO2 reduction are enhanced with increasing layer number from 1 to 3 but level off with much thicker multilayers. The stability of the monolayer and multilayer films is also examined. (C) 2000 The Electrochemical Society. S0013-4651(99)04-057-4. All rights reserved.

[80] Luminescence Properties of the J-Aggregate of Cyanine Dyes in Multilayer AssembliesN. Kometani, H. Nakajima, K. Asami, Y. Yonezawa, I. G. Scheblykin and A. G. VitukhnovskyJ. Luminesc. 87-9(MAY) (2000), 770-772

Multilayer assemblies incorporating the J-aggregate of 3,3'- disulfopropyl-5,5'-dichloro-thiacyanine dye were fabricated up to 50 layers by the alternate adsorption technique to examine their luminescence properties. Fluorescence spectra as well as fluorescence lifetime of multilayer assemblies remarkably depend on the number of layers. The result is interpreted in terms of the interaction between dye lavers within a limited distance, as well as the luminescence reabsorption effect. (C) 2000 Elsevier Science B.V. All rights reserved.


[81] Multilayered Supermolecular Structures Self-Assembled from Polyelectrolytes and Cyclodextrin Host-Guest ComplexesM. Dreja, I. T. Kim, Y. D. Yin and Y. N. XiaJ. Mater. Chem. 10(3) (2000), 603-605

Supermolecular multilayers with high levels of compositional and structural complexities have been fabricated with an example that involves formation of stable host-guest complexes from bolaamphiphiles and cyclodextrins, followed by sequential build-up of multilayered films by these complexes in combination with anionic polystyrene sulfonate polymer chains.

[82] Oriented Polyoxometalate-Polycation Multilayers on a Carbon SubstrateS. Q. Liu, Z. Tang, Z. X. Wang, Z. Q. Peng, E. K. Wang and S. J. DongJ. Mater. Chem. 10(12) (2000), 2727-2733

In this paper, a new method of fabricating multilayers on a carbon substrate is presented. First, a uniformly charged carbon surface was prepared through molecular design. Then an ultrathin film consisting of layer-pairs of oppositely charged polymeric cationic poly(diallyldimethylammonium chloride) (PDDA) and silicotungstate, SiW12O404- (SiW12), was grown layer- by-layer onto the grafted carbon substrate using a molecular self-assembly technique and an electrochemical method. The technique allows one to prepare highly adherent, dense and smooth films of polyoxometalates with special properties. By combining cyclic voltammetry (CV) and X-ray (XR) reflectometry, it was determined that the average surface density of SiW12 was 2.10 x 10(-10) mol cm(-2), and the thickness increase per adsorption of PDDA-SiW12 was 1.7 +/- 0.2 nm, indicating that the amount of SiW12 anion per one layer adsorption corresponded to a monolayer coverage. Atomic force microscopy (AFM) was also used to examine the surface morphology and determine the grain size distribution and roughness for multilayer films. An increase in root-mean-square (RMS) surface roughness from 7 to 9 Angstrom was observed as the number of layer-pairs in the film increased from 2 to 6. FTIR results showed that the good stability of the multilayer films was due to Coulomb interactions between the SiW12 anion and the polymeric cations PDDA. Moreover, the multilayer films, in acidic aqueous solution, showed good electrocatalytic activity toward the reduction of NO2-, and the catalytic currents increased with increasing the layer numbers of SiW12 adsorption. These characteristics of the multilayer films might find potential applications in the field of sensors and microelectronics devices.

[83] Microencapsulation by Means of Step-Wise Adsorption of PolyelectrolytesG. B. Sukhorukov, E. Donath, S. Moya, A. S. Susha, A. Voigt, J. Hartmann and H. MöhwaldJ. Microencapsul. 17(2) (2000), 177-185

Step-wise adsorption of polyelectrolytes is used for the fabrication of micro- and nanocapsules with determined size, capsule wall composition and thickness. The capsule walls made of polyelectrolyte multilayers exclude high molecular weight compounds. Assembling of lipid layers onto these polyelectrolyte capsules prevents the permeation of small dyes. Encapsulation of magnetite nanoparticles is demonstrated and the features of these novel capsules are discussed.

[84] Plastic Behavior of Polyelectrolyte Microcapsules Derived from Colloid TemplatesH. Baumler, G. Artmann, A. Voigt, R. Mitlohner, B. Neu and H. KiesewetterJ. Microencapsul. 17(5) (2000), 651-655

The deformability and osmotic properties of hollow microcapsules were studied by means of the micropipette video microscopic technique. The microcapsules were prepared by consecutive multiple adsorption of the polyanion, poly (styrene sulphonate), and the polycation, poly( allylamine hydrochloride), onto melamine formaldehyde resin latex of 5 mu m diameter, which was decomposed after completing the coating by transferring to hydrochloric acid of pH 1.1. The polyelectrolyte microcapsules reacted to micropipette suction with plastic deformation. If lipids are added to the polyelectrolyte layers, the capsules cannot be visibly deformed by micropipette suction up to 10(4) N/m(2). However, plastic shrinking was observed if the stress was generated by the osmotic pressure of a sucrose solution of 10(6) N/m(2).


[85] Structural and Photophysical Properties of a Water-Soluble Porphyrin Associated with Polycations in Solution and Electrostatically-Assembled Ultrathin FilmsP. G. Vanpatten, A. P. Shreve and R. J. DonohoeJ. Phys. Chem. B 104(25) (2000), 5986-5992

A water-soluble porphyrin, meso-tetra(4- sulfonatophenyl)porphyrin (TSPP), has been associated with two different polycations, poly(diallyldimethylammonium chloride) (PDDA) and poly(ethyleneimine) (PEI), to investigate the effects of polymer binding upon the TSPP structure and excited- state dynamics both in solution and in ultrathin (similar to 10- 30 Angstrom) films deposited on glass slides by electrostatic assembly. Association of the porphyrin with PEI intrinsically quenches the singlet state dynamics of TSPP, both in solution and in films, while quenching is observed upon association with PDDA only for high concentrations of porphyrins or in films where TSPP aggregates are observed. For PDDA:TSPP films without significant aggregate content, the fluorescence decay time (tau(1/e) similar to 5-6 ns) approaches that observed for monomeric or polymer-bound porphyrins in dilute solution (tau(1/ e) = 10.2 and 11.3 ns, respectively). However, rapid (< 1 ns) deactivation of the singlet states can be observed whenever appreciable aggregates are present, indicating that efficient energy transfer between the porphyrins leads to quenching at aggregate sites. A number of phenomenological observations regarding the presence of aggregates are presented. In particular, the extent of aggregation in the films depends on the concentration, pH, and temperature of the deposition solutions and also the age of the films, with older samples exhibiting reduced effects due to aggregation.

[86] Surface Texture of Poly(Styrenesulfonate Sodium-Salt) and Poly(Diallyldimethylammonium Chloride) Micron-Sized Multilayer Capsules - A Scanning Force and Confocal Microscopy StudyC. Y. Gao, S. Leporatti, E. Donath and H. MöhwaldJ. Phys. Chem. B 104(30) (2000), 7144-7149

Ultrathin polyelectrolyte capsules fabricated by stepwise assembly of poly(styrenesulfonate Sodium salt) and poly(diallyldimethylammonium chloride) are examined by confocal laser scanning microscopy and scanning force microscopy. The capsule surface is composed of grains of 124 +/- 10 nm in diameter with a roughness of similar to 13 nm. These grains are formed by laterally segregated polyelectrolyte complexes. Osmotically and annealing-induced capsule swelling facilitated further grain segregation together with a capsule surface area increase. Incubation in salt solution induced capsule shrinking and grain aggregation.

[87] Luminescence Properties of the Mixed J-Aggregate of 2 Kinds of Cyanine Dyes in Layer-by-Layer Alternate AssembliesN. Kometani, H. Nakajima, K. Asami, Y. Yonezawa and O. KajimotoJ. Phys. Chem. B 104(41) (2000), 9630-9637

The layer-by-layer alternate assemblies incorporating two kinds of cyanine dyes have been fabricated by alternately adsorbing a cationic polyelectrolyte and anionic cyanine dyes on the quartz plate. A thiacyanine dye (dye I) was employed as the donor and two kinds of thiacarbocyanine dye having a meso-alkyl group-m- ethyl (dye II), in-methyl (dye III)-as the acceptor. The mole fraction of the acceptor in the mixed J-aggregate, chi, was varied from 0 to 1. It is confirmed that these dye combinations form the mixed J-aggregate in the alternate assemblies. From steady-state fluorescence spectra of the molecular assemblies, excitation energy transfer from the donor J-aggregate to the acceptor J-aggregate is observed, whose kinetics obeys the Stern-Volmer relationship. The experimentally determined rate constant of energy transfer, k(ET), is fairly large, indicating efficient energy transfer due to exciton migration through the donor J-aggregate. The relative fluorescence quantum yield and the fluorescence lifetime of the acceptor aggregate decrease with increasing chi, implying the considerable self-quenching of acceptor fluorescence. The relative change of the coherent size of the dye II aggregate has been estimated from the J-band line width and the radiative decay rate constant. It is found that the coherent size of the dye II aggregate is increased by a factor of 4-5 with increasing chi from 0.008 to 1.

[88] Photochemical Behavior and Formation of Surface-Relief Grating on Self-Assembled Polyion/Dye Composite FilmJ. A. He, S. P. Bian, L. Li, J. Kumar, S. K. Tripathy and L. A. SamuelsonJ. Phys. Chem. B 104(45) (2000), 10513-10521

Holographic surface relief gratings (SRGs) were fabricated on composite films assembled by electrostatic layer-by-layer (ELBL) deposition of a polyelectrolyte, poly(dimethyl diallylammonium chloride) (PDAC), and an azo dye, Congo Red (CR). Surface modulation and first-order diffraction efficiency of the SRG were found to increase with the


thickness of the PDAC/CR films. Polarized absorption spectra indicated an oriented growth of CR on the PDAC film. Analysis of the film thickness, FTIR, and FT-Raman results confirmed that the electrostatic attraction between CR and PDAC, as well as the pi- pi interaction between CR chromophores resulting in the formation of J aggregates, lead to formation of PDAC/CR composite films. Photochemical changes of the PDAC/CR films after irradiation were investigated by W-vis absorption, FTIR, and FT-Raman spectroscopy. The results indicate that in addition to trans double left right arrow cis photoisomerization of CR in the composite film, an irreversible photochemical degradation of CR also simultaneously occurs. Recording SRG on PDAC/CR films by s- and p-polarized beams show different behavior compared to spin-coated films of polymers containing functionalized azo chromophores. Our results indicate that the volume collapse due to the photodegradation of CR in the polymeric matrix, as well as gradient force- induced migration due to trans double left right arrow cis isomerization cycling of CR contribute to the formation of SRG on the composite films. This approach provides a methodology to fabricate SRGs for optical information storage applications by using the facile ELBL technique to assemble commercially available azo dyes and polyelectrolytes.

[89] Surface Electronic-Properties of Self-Assembled, Oppositely Charged Macrocycle and Polymer Multilayers on Conductive OxidesL. S. Li, R. Wang, M. Fitzsimmons and D. Q. LiJ. Phys. Chem. B 104(47) (2000), 11195-11201

Using the layer-by-layer self-assembly technique, we have deposited multilayer thin films on conductive indium tin oxide (ITO) surfaces by alternatively dipping ITO substrates in a polymer PDDA or poly(diallydimethylammonium) chloride solution and a macrocyle NiPc or nickel phthalocyanine solution. In addition to characterizing PDDA-NiPc systems with X-ray reflectometry and cyclic voltammetry, we monitored the growth of PDDA/NiPc multilayers on conductive oxides with Fourier transform infrared (IR) spectroscopy at an external grazing- angle reflection configuration. IR spectra with polarization perpendicular to the conductive ITO surfaces revealed vibration bands at 1227 and 1200 cm(-1) corresponding to salt bridges of - SO3-. . . Me2N+ = binding between PDDA and NiPc. An oscillation of the surface electronic potential was observed with a Kelvin Probe as the surface layer alternated between PDDA and NiPc. The average gap of the surface potential difference between NiPc and PDDA monolayers is about 400 mV. Oscillation of surface potential or work function is caused by the modulation in electron affinity of ITO due to the dipolar effect, generated by the highly charged layers of PDDA or NiPc.

[90] Reversal of Interfacial Dipole Orientation in Polyelectrolyte Superlattices Due to Polycationic LayersJ. L. Casson, D. W. Mcbranch, J. M. Robinson, H. L. Wang, J. B. Roberts, P. A. Chiarelli and M. S. JohalJ. Phys. Chem. B 104(50) (2000), 11996-12001

Repeated bilayers of a polycation and a polyanion were assembled by adsorption from their aqueous solutions. The polycations used were PEI (poly(ethylenimine)), PAH (poly(allylamine hydrochloride)), and generation 3.0 dendrimer (poly(propylenimine)). The polyanion was PAZO (poly[1-[4-(3- carboxy-4-hydroxyphenylazo)-benzenesulfonamido]-1,2-ethanediyl, sodium salt]). Second harmonic generation (SHG) and UV-vis spectroscopy were used to study the structure and formation of the superlattices. The linear increase in absorbance versus the number of bilayers suggested that a uniform and consistent amount of polymer adsorbed during each deposition cycle. The observation of a second harmonic (SH) signal from the film showed that the conjugated chromophores in the PAZO polymer were aligned with a net dipole. However, the SHG signal did not continue to increase as the number of bilayers was increased. On the basis of thorough studies of the UV and SH properties for each bilayer for 10 total bilayers, we propose that the asymptotic nonlinear optical response is due to loss of charge density on the polycation. The SH signal from multilayers terminated with the polycation is smaller than when PAZO is the terminal layer. We attribute this to a change in orientation of the dipole of the outermost PAZO chromophores at the interface of the PAZO and the terminal polycation layer. We also propose multilayer assemblies that will lead to self-assembled polyelectrolyte superlattices with a high nonlinear optical susceptibility.

[91] Adsorption of Charged PolymersJ. F. Joanny, M. Castelnovo and R. NetzJ. Phys. Condens. Matter 12(8A) (2000), A1-A7

We review some of the theoretical results that we have obtained recently on the adsorption of polyelectrolytes on surfaces of opposite charge. We consider two problems, the formation of polyelectrolyte multilayers and the formation of complexes between rigid polyelectrolytes and small spheres. For polyelectrolyte multilayers, the overcompensation of the adsorbing surface charge and the anchoring between consecutive layers are studied. For polyelectrolyte-sphere complexes, the wrapping of the polymer on the sphere is shown to occur continuously at low


ionic strength and discontinuously at high ionic strength. The findings of some recent experiments are briefly compared with our results.

[92] Optical and Electrical Characterizations of Ultrathin Films Self-Assembled from 11-Aminoundecanoic Acid Capped TiO2 Nanoparticles and Polyallylamine HydrochlorideT. Cassagneau, J. H. Fendler and T. E. MalloukLangmuir 16(1) (2000), 241-246

11-Aminoundecanoic acid capped titanium dioxide (capped-TiO2) nanoparticles (63 +/- 2 Angstrom total diameter and 20 - 24 Angstrom core diameter) and polyallylamine hydrochloride, PAK, have been layer-by-layer self-assembled onto precoated (by poly(diallyldimethylammonium chloride), PDDA, or PAH) substrates. The ultrathin S-PDDA(capped-TiO2/PAH)(n) (n = 5, 10, 15) films have been characterized by absorption and surface plasmon spectroscopies, cyclic voltammetry, and scanning force microscopy. AS-PDDA(capped-TiO2/PAH)(10) film coated by a layer of gold has been shown to function as a Schottky diode.

[93] Selective Ion-Transport Across Self-Assembled Alternating Multilayers of Cationic and Anionic PolyelectrolytesL. Krasemann and B. TiekeLangmuir 16(2) (2000), 287-290

Ultrathin membranes consisting of an alternating sequence of cationic and anionic polyelectrolytes were prepared by means of electrostatic layer-by-layer adsorption and investigated on their permeability for NaCl, Na2SO4, and MgCl2 in aqueous solution. It is demonstrated that the multi-bipolar structure of the polyelectrolyte membranes favors the separation of mono- and divalent ions by Donnan exclusion of the divalent ions. Various effects on the rate of ion permeation and the selectivity were investigated. Addition of salt to the polyelectrolyte solutions used for membrane preparation led to improved ion separation, while an increase of the pH had the opposite effect. Use of polyelectrolytes with high charge density also improved the ion separation. Especially good results were obtained if membranes containing polyallylamine (PAH) as the cationic polyelectrolyte were used. For 60 layer pairs of PAH/polystyrenesulfonate, for example, a separation factor a for Na+/Mg2+ up to 112.5 and for Cl-/SO42- up to 45.0 was found. The origins of the various effects are discussed in terms of different charge density and concentration of excess charges in the polyelectrolyte membrane.

[94] Fabrication of Photochromic WO3/4,4'-Bambp Superlattice FilmsZ. H. Chen, Y. A. Yang, J. B. Qiu and J. N. YaoLangmuir 16(2) (2000), 722-725

A layered superlattice WO3/4,4'-BAMBp self-assembled multilayer film has been fabricated onto aminopropylsilanated quartz or silicon substrate from transition-metal W compound and 4,4'- BAMBp solution using a polyelectrolyte approach. The superlattice film showed good photochromic properties. UV- visible spectra were employed to study the growth process and the aggregation of organic molecules. A well-ordered superlattice structure was identified by X-ray diffraction. A possible structural model was proposed according to UV-visible, XRD, and XPS spectra.

[95] In-Situ Determination of the Structural-Properties of Initially Deposited Polyelectrolyte MultilayersG. Ladam, P. Schaad, J. C. Voegel, P. Schaaf, G. Decher and F. CuisinierLangmuir 16(3) (2000), 1249-1255

The buildup of the first layers of polystyrenesulfonate (PSS)/ polyallylamine (PAH) multilayer is studied in situ by means of streaming potential measurements (SPM) and by scanning angle reflectometry (SAR). The results are discussed in the framework of a schematic representation of the multilayer in three zones: a precursor zone (I), a core zone (II), and an outer zone (III). This view seems to be supported by our experimental findings. The zeta potential of the multilayer determined by the SPM shows a symmetrical and constant charge inversion during the multilayer buildup. This seems to indicate an exact charge compensation in zone II and an excess charge that is entirely located in the outer zone III. It is also shown by SAR that a regular buildup regime, in which the thickness increment per layer is constant, is reached after the deposition of the first six polyelectrolyte layers, which gives an indication of the extension of zone I. The influence of the salt concentration C-NaCl present in the polyelectrolyte solutions during


multilayer buildup is also investigated. It is found that an increase of the salt concentration in the polyelectrolyte solutions leads to larger amounts of deposited polyelectrolytes and to thicker multilayers. The amount deposited per polyelectrolyte layer delta Q (PSS or PAH) is correctly predicted by the law delta Q = a.C-Nacl(a) + b where a lies between 0.05 and 0.15. In addition, when a multilayer built up in salty solutions is brought in contact with pure water, it expands, indicating that the rinsing step mainly affects zone III of the multilayer, which appears thus to behave like a polyion layer. The structural changes of the multilayer consecutive to the replacement of the salt solution by pure water occur with characteristic times ranging from a few tens of minutes to several hours depending on the initial salt concentration. Finally, it is also found that the structural modifications of the film are fully reversible so that the initial multilayer structure is recovered when water is replaced again by the initial salt solution.

[96] Enzyme Encapsulation in Layer-by-Layer Engineered Polymer Multilayer CapsulesF. Caruso, D. Trau, H. Möhwald and R. RennebergLangmuir 16(4) (2000), 1485-1488

We report on the encapsulation of enzyme (catalase) by the controlled polymer multilayer coating of biocrystals, achieved by the sequential adsorption of oppositely charged polyelectrolytes onto enzyme crystal templates. An extremely high enzyme loading in each polymer capsule is obtained, and the activity of the encapsulated enzyme is preserved. The polymer-encapsulated enzyme is stable against protease degradation: The polymer-coated enzyme retains 100% of its activity after incubation for 100 min with protease, whereas uncoated, solubilized catalase loses more than 90% of its initial activity within 100 min under the same conditions. This simple, general, and versatile approach can potentially be applied for the encapsulation of various crystallized substances for catalysis and drug delivery applications.

[97] Electrochemical and in-Situ Ellipsometric Investigation of the Permeability and Stability of Layered Polyelectrolyte FilmsJ. J. Harris and M. L. BrueningLangmuir 16(4) (2000), 2006-2013

Utilization of layered polyelectrolyte films as sensor or ion- separation materials will depend critically on their stability and ion permeability in aqueous solution. We report electrochemical and in situ ellipsometric studies on the permeability and stability of poly(allylamine hydrochloride)/ poly(styrenesulfonate) (PAH/ PSS) and PAH/poly(acrylic acid) (PAA) films. The permeability of these layered polyelectrolyte films to Fe(CN)(6)(3-) and Ru(NH3)(6)(3+) depends on the solution pH, the number of bilayers in the film, whether supporting electrolyte is present during film deposition, and the nature of constituent polycations and polyanions. Cyclic voltammetry and impedance spectroscopy show that film permeability is similar in pH 3.2- and pH 6.3-buffered solutions but increases dramatically in alkaline solutions. In situ ellipsometry helps to explain these results. Upon immersion in pH 3.2- and pH 6.3-buffered solutions, the thickness of PAH/PSS films increases by 40%, but swelling is constant over time. At pH 10, these films initially swell by 40% but then continue to swell for several minutes before delaminating. The onset of increased swelling corresponds with dramatic increases in film permeability. Both peak current (cyclic voltammetry) and charge-transfer resistance (ac impedance) depend nonlinearly on the number of polyelectrolyte bilayers. The structure of the first two bilayers is more porous than that of later bilayers. Adding supporting electrolyte to deposition solutions results in thicker bilayers and changes film permeability. For PAH/PSS films, the use of supporting electrolyte during film formation results in a much less permeable film (comparing films of similar thickness). In PAH/PAA films, however, the use of supporting salt results in highly permeable films (even with thicknesses as high as 44 nm). Thus proper choice of constituent polyelectrolytes and deposition conditions permits control over the permeability of layered polyelectrolyte films.

[98] One-Pot Synthesis of Ag-at-TiO2 Core-Shell Nanoparticles and Their Layer-by-Layer AssemblyI. Pastorizasantos, D. S. Koktysh, A. A. Mamedov, M. Giersig, N. A. Kotov and L. M. LizmarzanLangmuir 16(6) (2000), 2731-2735

Silver nanoparticles coated with a uniform, thin shell of titanium dioxide are synthesized via a remarkably simple one- pot route, where the reduction of Ag+ to Ag-0 and the controlled polymerization of TiO2 on the surface of silver crystallites take place simultaneously. The prepared dispersions of coated nanoparticles display a surface plasmon band, which is significantly red-shifted with respect to that of bare AK. High quality ultrathin films of the core-shell clusters are prepared via layer-by-layer assembly. The nanoparticles are arranged in closely packed layers interlaced with polyelectrolyte producing a stratified core-shell hybrid material with unique structure and catalytic and electron- transport properties.


[99] Energies of Adsorption of Poly(O-Methoxyaniline) Layer-by-Layer FilmsM. Raposo and O. N. OliveiraLangmuir 16(6) (2000), 2839-2844

The adsorption mechanisms in layer-by-layer films of poly(o- methoxyaniline) (POMA) alternated with poly(ethene sulfonic acid) (PVS) are controlled by H-bonding, even for charged POMA where electrostatic interactions were expected to predominate. This is shown here by analyzing adsorption isotherms using three analytical models for adsorption, namely, Langmuir, Frumkin, and Fillippova models, and thermally stimulated desorption results, from which energies of interaction were estimated. The adsorption free energy is ca. -35 kJ/mol, whereas the activation energy for desorption obtained from thermally stimulated desorption was +75 kJ/mol. According to the three models, adsorption is favored when the number of POMA/ PVS bilayers increases, consistent with the increase in the amount of adsorbed material and film roughness. The importance of H-bonding was confirmed by FTIR measurements and adsorption experiments at high pHs where POMA is no longer doped.

[100] Construction of Multilayer Thin-Films of Enzymes by Means of Sugar-Lectin InteractionsJ. Anzai and Y. KobayashiLangmuir 16(6) (2000), 2851-2856

A layer-by-layer deposition of concanavalin A (Con A) and glycoproteins such as glucose oxidase (GOx) and horseradish peroxidase (HRP) afforded multilayer thin films on the surfaces of a quartz slide and a platinum electrode, through biospecific complexation of Con A and sugar residues in the glycoenzymes. Lactate oxidase (LOx), which contains intrinsically no sugar chain, was also built into a multilayer assembly by being modified extrinsically with mannose residues. The enzymes formed monomolecular or sub-monomolecular layers in each layer of the multilayer films. Electrochemical measurements using Con A-enzyme multilayer-modified electrodes revealed that the enzymes are catalytically active in the multilayer films. The Con A-enzyme multilayer films are relatively stable against low concentrations of mannose and urea, although the films destructed gradually in high concentrations of urea solutions (>3 M).

[101] Stratified Assemblies of Magnetite Nanoparticles and Montmorillonite Prepared by the Layer-by-Layer AssemblyA. Mamedov, J. Ostrander, F. Aliev and N. A. KotovLangmuir 16(8) (2000), 3941-3949

Hybrid thin films are prepared from 8 to 10 nm Fe3O4 nanoparticles and exfoliated montmorillonite clay by using layer-by-layer assembly on poly(diallyldimethylammonium bromide), PDDA. Distinct stratification of the Fe3O4/PDDA/clay films is obtained due to the sheetlike structure of the clay particles. This feature distinguishes these assemblies from their polyelectrolyte-polyelectrolyte analogues, where the layers of individual polyelectrolytes are strongly interdigitated. Being adsorbed on PDDA strictly parallel to the substrate surface, montmorillonite produces a dense layer of overlapping alumosilicate sheets, which virtually flawlessly separates one magnetite layer from another. The difference in magnetic properties between assemblies of various architectures is attributed to the insulation effect of clay layers inserted between magnetic layers. The montmorillonite sheets disrupt the electron exchange interactions between the magnetite nanoparticles in adjacent layers, thereby limiting the magnetization reversal to two dimensions. Some optical properties of Fe3O4/PDDA films are investigated as well. When they are deposited on thin plastic substrate, oscillations of optical density were observed in the red part of the UV-vis spectrum. This effect, which was never been observed for conventional, thick substrates such as glass slides, stems from the interference of the light beams passed through and reflected off of the assembled film.

[102] Scanning Force Microscopy Investigation of Polyelectrolyte Nanocapsule and Microcapsule Wall TextureS. Leporatti, A. Voigt, R. Mitlohner, G. Sukhorukov, E. Donath and H. MöhwaldLangmuir 16(9) (2000), 4059-4063

Ultrathin polymer capsules prepared by stepwise deposition of oppositely charged polyelectrolytes onto melamine formaldehyde latex particles and biological cells with subsequent dissolution of the core have been examined by scanning force microscopy (SFM) in the dried state. Folds generated during the drying induced collapse of the shells are observed. The thickness of a single polyelectrolyte layer in the dried state was determined as 1.3 +/- 0.3 nm. Imaging at high resolution revealed the existence of domains and invaginations. This typical lateral pattern has been quantified by means of an autocorrelation analysis of the SFM images. A characteristic domain size of 50-100 nm is


found. If the polyelectrolytes have been cross-linked prior to the core decomposition, a surface separation into defined domains is not observed. The nature and size of the domains are discussed in relation to the drying and the molecular parameters of the layer constituents.

[103] 2-Dimensional Auto-Organized Nanostructure Formation of Hyaluronate on Bovine Serum-Albumin Monolayer and Its Surface- TensionT. Nonogaki, S. H. Xu, S. Kugimiya, S. Sato, I. Miyata and M. YoneseLangmuir 16(9) (2000), 4272-4278

The layer-by-layer interaction between bovine serum albumin BSA and sodium hyaluronate NaHA was studied by a quartz crystal microbalance QCM method. The surface structures of the BSX layer and the NaHA layer and their surface tensions were investigated using atomic force microscopy AFM. BSA showed Langmuir type adsorption on poly(gamma-methyl-L-glutamate) PMLG thin film and were found to be a monolayer in the saturated adsorption state. The adsorption of NaHA on the BSA monolayer was also the Langmuir type. From their linear reciprocal plots, adsorption constants K and saturated adsorption masses Gamma(infinity) were determined. The BSA molecules on the PMLG film surface could be imaged using AFM in the monolayer state. Furthermore. the surface structure of NaHA adsorbed on the BSA monolayer was found to form hexagonal-like networks. From the adhesion force F-ad between the AFM tip and the surfaces of the BSA layers or the NaHA layers, their surface tensions gamma(s) were estimated. The surface tension of the PMLG films increased with increasing the adsorption of BSA but the surface tension of the saturated adsorption BSA layer was found to decrease with increasing the adsorption of NaHA.

[104] Characterization of Flexibility of Ultrathin Protein Films by Optical SensingE. Brynda, M. Houska, A. Wikerstal, Z. Pientka, J. E. Dyr and A. BrandenburgLangmuir 16(9) (2000), 4352-4357

Films consisting of three cross-linked molecular layers of human serum albumin (HSA) or three HSA layers alternating with three heparin layers were immobilized on surfaces of grating coupler sensors and hydrophobized glass. Optical responses of the coated sensors to pH changes were observed. A decrease in the effective refractive index, Delta N-eff, measured by a grating coupler was observed when the pH of buffers contacting the films was increased. The process was quite reversible, which indicated that the mass of the film remained constant when the buffers were repeatedly exchanged. Theoretical treatment of the grating coupler optics related the decrease in Delta N-eff to expansion of the films. The interpretation of sensor measurements was confirmed by atomic force microscopy which revealed reversible changes in the thickness of NSA/ heparin film induced by pH changes of the buffers.

[105] Influence of a Base Electrolyte on the Adsorption Behavior of an Anionic Surfactant as Observed by 2nd-Harmonic GenerationG. Moller, S. Schrader, H. Motschmann and D. PrescherLangmuir 16(10) (2000), 4594-4598

The adsorption process of sodium-[4-(4'- trifluormethylphenylazo)phenyl-1-oxyethylsulfonate] (NaTAPOS) at the water/1,2-dichlorethane interface was investigated by second harmonic generation and ellipsometry. The combination of both techniques yields the surface excess and the orientation of the amphiphiles within the adsorption layer. These data were used for an investigation of equilibrium properties of the system. The average tilt angle of the chromophore within the adsorption layer remains constant in the whole concentration range. The mean tilt angle was found to be 39 +/- 3 degrees and the area per molecule at maximum surface coverage is 45.2 +/- 6 Angstrom(2). The present study focuses on the impact of a base electrolyte on the adsorption process. Neither the limiting area per molecule nor the orientational order was changed by base electrolyte dissolved in the aqueous phase. The maximum surface coverage with and without base electrolyte is achieved at the same bulk concentration and is within the error limit identical; however, at lower concentrations a significantly higher surface excess is observed in the absence of base electrolyte. This is counterintuitive since one might expect an electrostatic shielding of the prevailing interaction. The adsorption isotherms with and in absence of base electrolyte can be described by Frumkin's equation of state. This model accounts for regular surface behavior and takes into account the lateral interaction of the absorbed species. The model fit yields two quantities: the free enthalpy of adsorption and the interaction parameter. Only slight changes of the free enthalpy of adsorption were observed by the presence of base electrolyte; however, a significant increase of the corresponding interaction parameter was observed. These findings are in contradiction to the Debye-Huckel theory and are explained by a model in analogy to the polyelectrolyte layer-by-layer adsorption.


[106] Covalently Attached Multilayer Assemblies by Sequential Adsorption of Polycationic Diazo-Resins and Polyanionic Poly(Acrylic Acid)J. Q. Sun, T. Wu, F. Liu, Z. Q. Wang, X. Zhang and J. C. ShenLangmuir 16(10) (2000), 4620-4624

Diazo-resins (DAR) as polycation and poly(acrylic acid) (PAA) as polyanion were alternately assembled into a multilayer structure by using the layer-by-layer self-assembly technique. PAA as a weak polyelectrolyte was very sensitive to the pH value of the solution, and that pH could be used to tune the thickness of the PAA layer. Upon UV irradiation, a fraction of the carboxylate groups reacted with diazonium groups at the adjacent interfaces of the multilayer, so partially covalently attached multilayer assemblies could be formed. Their stability improved greatly compared with the fraction that was not UV- irradiated. The photoreaction occurring between the layers was confirmed by means of UV-visible and Fourier transform infrared spectroscopy. The thickness of the W-irradiated films was characterized with X-ray diffraction, results from which showed that the thickness of the films can be adjusted in nanometer scale by simply changing the pH value of the solutions.

[107] Electroactive Myoglobin Films Grown Layer-by-Layer with Poly(Styrenesulfonate) on Pyrolytic-Graphite ElectrodesH. Y. Ma, N. F. Hu and J. F. RuslingLangmuir 16(11) (2000), 4969-4975

Stable multilayer electroactive films were grown on rough pyrolytic graphite (PG) electrodes by alternate adsorption of layers of polyanion poly(styrenesulfonate) (PSS) and positively charged myoglobin (Mb) from their aqueous solutions. Incorporation of large amounts of electroactive Mb was facilitated by high electrode surface areas and by adsorbing coiled PSS from 0.5 M NaCl solutions. Cyclic voltammetry of {PSS/Mb}(n), films showed a pair of well-defined, chemically reversible peaks at about -0.25 V vs SCE at pH 5.5, characteristic of the Mb heme Fe-III/Fe-II redox couple. Electroactivity was extended to 7 {PSS/Mb} bilayers on rough PG surfaces, in comparison to 2 electroactive layers on smooth gold coated with mercaptopropanesulfonic acid. Square wave voltammograms of {PSS/Mb}, films gave good fits by nonlinear regression analysis to a model featuring dispersion of formal potentials, providing average formal potentials and an apparent rate constant. Oxygen and trichloroacetic acid were catalytically reduced by Mb in {PSS/Mb}(n) films with significant decreases in the electrode potential required. Making such films on PG rather than on gold provides a larger number of electroactive layers with no need for chemical pretreatment of the electrode.

[108] Fabrication of Microporous Thin-Films from Polyelectrolyte MultilayersJ. D. Mendelsohn, C. J. Barrett, V. V. Chan, A. J. Pal, A. M. Mayes and M. F. RubnerLangmuir 16(11) (2000), 5017-5023

A simple process has been developed to create large area, highly uniform microporous thin films. Multilayers of weak polyelectrolytes were assembled onto silicon substrates by the sequential adsorption of poly(acrylic acid) and poly(allylamine) from aqueous solution. These multilayers were then immersed briefly into acidic solution (pH approximate to 2.4) to effect a substantial and irreversible transformation of the film morphology. The resulting microporous structures are 2- 3 times the thickness of the original films, possess a correspondingly reduced relative density of 1/2 to 1/3, and are stable against further rearrangement under ambient; conditions. In addition, the microporous films may undergo a secondary reorganization in neutral water, leading to a morphology with more discrete throughpores. A mechanism is proposed for these transformations based on interchain ionic bond breakage and reformation in this highly protonating environment;, leading to an insoluble precipitate on the substrate which undergoes spinodal decomposition with the solvent. FTIR (Fourier transform infrared spectroscopy) analysis supports the underlying chemical basis of this pH-induced phase separation, and AFM (atomic force microscopy), in situ ellipsometry, and SEM (scanning electron microscopy) have been used to monitor the morphological changes. The unique combination of properties exhibited by these microporous films makes them potential candidates for microelectronic and biomaterial applications.

[109] Mobile Phospholipid-Bilayers on a Polyion/Alkylthiol Layer PairL. Q. Zhang, M. L. Longo and P. StroeveLangmuir 16(11) (2000), 5093-5099

The formation of phospholipid bilayers on a polymer/alkylthiol layer pair was investigated by surface plasmon resonance (SPR). The organic layer pair between the lipid membrane and the solid gold surface consisted of a self-


assembled monolayer of 11- mercaptoundecanoic acid (MUA) on a gold surface followed by a thin layer of hydrated cationic poly(diallyldimethylammonium chloride) (PDDA). The lipid layers were formed by vesicular fusion of small unilamellar vesicles of an anionic lipid 1- stearoyl-2-oleoyl-phosphatidylserine (SOPS), a zwitterionic lipid 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), and mixtures of these two lipids with different compositions. In the case of pure SOPS and lipid mixtures with a POPC composition below 25%, the lipid layer thickness was approximately that of a single bilayer, while multilayers tended to build up with higher concentrations of POPC. The electrostatic interaction of the cationic PDDA with the negatively charged lipid membrane is most probably the driving force for the adsorption of a single bilayer. Fluorescence recovery after photobleaching (FRAP) experiments showed that single bilayers supported on the PDDA/alkylthiol layer pair were mobile at room temperature with lateral diffusivities of approximately (1-2) x 10(-9) cm(2)/s. A membrane fusion peptide wt-20 of the influenza virus was bound to the supported bilayers as detected by SPR. This suggests the potential of this model membrane system for use as a biosensor.

[110] Self-Assembled Monolayers and Multilayered Stacks of Lyotropic Chromonic Liquid-Crystalline Dyes with Inplane Orientational OrderT. Schneider and O. D. LavrentovichLangmuir 16(12) (2000), 5227-5230

A simple method to create large areas of in-plane oriented molecular mono- and multilayers is presented. The method is based on layer-by-layer adsorption of polyions and a lyotropic chromonic (nonamphiphilic) liquid crystal, which allows one to orient the molecules uniformly in the plane of deposition. The long-range in-plane orientation of the chromonic molecules determines the unique structural and optical properties of the films. Control of the orientational order allows one to use the films as polarizers, alignment layers, optical compensators, retarders, filters, etc.

[111] Freestanding Layer-by-Layer Assembled Films of Magnetite NanoparticlesA. A. Mamedov and N. A. KotovLangmuir 16(13) (2000), 5530-5533

A new technique for preparation of free-standing ultrathin films is presented. These films were made by layer-by-layer (LBL) deposition process, which is utilized for coatings on solid substrates and colloids. A film composed of alternating layers of magnetite nanoparticles and poly(diallyldimethylammonium bromide) was assembled on cellulose acetate, which was subsequently dissolved in acetone. From the suspended state, the LBL film can be transferred onto any solid or porous support. The strength of the film was observed to significantly increase when every other layer of magnetite was replaced with a layer of alumosilicate sheets serving as a molecular framework for the assembly.

[112] Imaging Nanoscale Patterns on Biologically Derived MicrostructuresY. M. Lvov, R. R. Price, J. V. Selinger, A. Singh, M. S. Spector and J. M. SchnurLangmuir 16(14) (2000), 5932-5935

We have demonstrated a new approach for imaging nanoscale patterns on three-dimensional submicrometer structures using charged particles. Nanoparticle structures were assembled onto lipid tubules through the sequential adsorption of oppositely charged polymers and silica spheres. For tubules of the zwitterionic lipid DCB8,11PC, this process leads to the formation of caps on the ends of the tubules, with 50-100 silica spheres in each cap. For tubules of DC8,11PC mixed with 2% of the charged lipid DC8,9PEOH, the sequential adsorption leads to both end caps and helices of nanoparticles winding around the interior of the tubules. These results give new insight into the pattern of charge in lipid tubules.

[113] Construction of Multilayer Thin-Films Containing Avidin by a Layer-by-Layer Deposition of Avidin and Poly(Anion)SJ. Anzai, T. Hoshi and N. NakamuraLangmuir 16(15) (2000), 6306-6311

A layer-by layer deposition of avidin and poly(anion)s including poly(styrenesulfonate) (PSS), poly(vinyl sulfate) (PVS), and dextransulfate (DS) afforded multilayer thin films on the surface of a quartz slide, through electrostatic


force of attraction between positive charges on the avidin molecule and negative charges on the polymer chains. It was possible to regulate the thickness of the films arbitrarily by changing the number of depositions. The loading of avidin in the multilayer thin films depended on the concentration of avidin and poly(anion)s in the bathing solutions from which the films were deposited. In the PVS- and PSS-based multilayer films, a large amount of avidin was immobilized in each deposition, depending on the concentrations of avidin and poly(anion) in the bathing solutions. In contrast, nearly a monomolecular layer was formed in each layer in the avidin-DS films independent of the concentration of bathing solutions. Avidin molecules assembled into the thin film retained its binding activity to biotin and analogues. The binding properties of avidin in the multilayer films were nearly comparable to those in solution; the films bound biotin, desthiobiotin, iminobiotin, and 2-(4'- hydroxyphenyl azo)benzoic acid effectively.

[114] Sequential Electrostatic Assembly of Amine-Derivatized Gold and Carboxylic Acid-Derivatized Silver Colloidal Particles on Glass SubstratesA. Kumar, A. B. Mandale and M. SastryLangmuir 16(17) (2000), 6921-6926

The formation of alternating layers of positively charged gold and negatively charged silver colloidal particles on glass substrates via electrostatic interaction is described. The charging of the gold and silver colloidal particles is accomplished by self-assembly of 4-aminothiophenol (4-ATP) and 4-carboxythiophenol (4-CTP) monolayers on the colloidal particles respectively and subsequent ionization of the functional groups at appropriate pH values of the colloidal solution. Glass substrates, which are negatively charged at pH > 3, are immersed first in the positively charged amine- derivatized gold solution leading to the formation of a monolayer of the gold particles and charge reversal of the glass surface. Thereafter, the gold particle covered glass surface is immersed in the negatively charged carboxylic acid- derivatized colloidal silver solution and the silver particles electrostatically self-assembled on the glass surface. This process map be continued to yield multilayer structures of the colloidal particles. The kinetics of electrostatic self- assembly of the colloidal particles on glass, the formation of the multilayer films, and their thermal stability have been followed with UV-vis spectroscopy, X-ray diffraction, ellipsometry, and X-ray photoemission spectroscopy measurements.

[115] Conductance and Capacitance of Polyelectrolyte and Lipid- Polyelectrolyte Composite Capsules as Measured by ElectrorotationR. Georgieva, S. Moya, S. Leporatti, B. Neu, H. Baumler, C. Reichle, E. Donath and H. MöhwaldLangmuir 16(17) (2000), 7075-7081

Polyelectrolyte capsules were fabricated in aqueous media by stepwise adsorption of polyelectrolytes onto fixed erythrocytes and subsequent template dissolution. Lipid polyelectrolyte composite capsules were prepared assembling lipid layers on these polyelectrolyte capsules. Dipalmitoyl phosphatidyl acid (DPPA), dipalmitoyl phosphatidyl choline (DPPC), and a mixture of both were used. Confocal laser scanning microscopy showed that the Lipids form a homogeneous coverage on the capsule surface. An electrorotation technique was used to study the electrical properties of polyelectrolyte and lipid- polyelectrolyte composite capsules. A conductivity of 1 S/m for polyelectrolyte capsule walls was found. Lipid-polyelectrolyte composite capsules yielded conductivities in the range from 10(- 4) to 10(-1) mS/m and capacities of 2.7 mu F/cm(2) for DPPA and 0.5 mu F/cm(2) for DPPC. These conductivities of lipid- polyelectrolyte composite capsules were much higher than for black lipid membranes. They increased with the bulk electrolyte concentration, which was attributed to the presence of pores or defects in the lipid structures. The effective area of pores was estimated as 0.01% of the total capsule surface.

[116] Nucleation and Growth of Cobalt Hydroxide Crystallites in Organized Polymeric MultilayersL. Q. Zhang, A. K. Dutta, G. Jarero and P. StroeveLangmuir 16(17) (2000), 7095-7100

In this paper, we report the hydrolysis of Co2+ ions absorbed in organized, multilayered polymer films to form cobalt hydroxide nanocrystals. Polymer films were prepared using the layer-by-layer deposition technique that consists of adsorbing polycations and polyanions alternately on a quartz substrate. By monitoring the UV-vis absorbance of the polymer films as a function of the number of absorption-hydrolysis cycles, it was shown that the crystals continued to grow with additional cycles. It is also found in this study that using more polymer layer pairs results in more crystal growth. Hydrolysis of the Co2+ ions in a nitrogen-rich environment gives rise to mainly needlelike crystallites of alpha-Co(OH)(2) that are initially about 100 nm in length and th en increase in size with the number of absorption-hydrolysis cycles. However, in an oxygen- rich microenvironment, hexagonal crystallites were found to be predominant. X-ray diffraction and transmission electronmicroscopic studies revealed that these hexagonal crystallites


mainly consist of beta-Co(OH)(2) with a contribution of CoOOH. Our studies suggest that by varying the nitrogen-to-oxygen ratio the formation of alpha-Co(OH)(2) and beta-Co(OH)(2) can be controlled.

[117] Stepwise Assembly of Isotactic Poly(Methyl Methacrylate) and Syndiotactic Poly(Methacrylic Acid) on a SubstrateT. Serizawa, K. Hamada, T. Kitayama, K. Katsukawa, K. Hatada and M. AkashiLangmuir 16(18) (2000), 7112-7115

Stepwise assembly of isotactic poly(methyl methacrylate) and syndiotactic poly(methacrylic acid) from acetonitrile and mixed acetonitrile/water solutions, respectively, onto a gold substrate was studied. Quantitative quartz crystal microbalance analysis of the molar ratio (monomer unit) between assembled polymers suggested Stepwise stereocomplex formation. The assembled amount and the assembly ratio between PMAA and PMAA were dependent on the acetonitrile content of the poly(methacrylic acid) solution. Infrared spectra of the assembly and cast films of each polymer also showed stereocomplex formation in the assembly. Atomic force microscopic observation showed the assembled polymer to have a molecularly smooth surface. The solvent species used was an important factor in stereocomplex formation at the liquid- polymer film interface.

[118] Preparation and Characterization of Ultrathin Films Layer-by- Layer Self-Assembled from Graphite Oxide Nanoplatelets and PolymersT. Cassagneau, F. Guerin and J. H. FendlerLangmuir 16(18) (2000), 7318-7324

Graphite, oxidized by HNO3 and NaClO3 to 25% (GO-25), 42% (GO- 42), and 33% (GO-33), has been dispersed to partially exfoliated nanoplatelets and, along with poly(diallyldimethylammonium chloride) (PDDA) and poly(ethylene oxide) (PEO), layer-by-layer self-assembled to ultrathin S- (PDDA/GO)(10), S-PDDA/(GO/PEO)(10), and S-(PDDA/GO/PEO)(10) films (where S is the indium tin oxide- or chromium/gold-coated glass or quartz substrate and GO refers to platelets of oxidized graphite). The GO powders have been characterized by X- ray diffraction prior and by transmission electron microscopy after their dispersions. Thicknesses of each of the successively adsorbed layers were comparatively determined by absorption spectrophotometry, surface plasmon resonance spectroscopy, quartz crystal microbalance, and scanning force microscopy. Good agreements were obtained by these three different techniques.

[119] Formation of Polyelectrolyte MultilayersM. Castelnovo and J. F. JoannyLangmuir 16(19) (2000), 7524-7532

A mechanism for the formation of polyelectrolyte multilayers is proposed. All of the experiments on such systems show that there is strong interpenetration of consecutive layers. We explain the very strong stability of the multilayers by the complexation between polyelectrolytes of opposite signs. Scaling laws on bulk polyelectrolyte complexation and their applications to the case of multilayers are derived in analogy with the description of neutral polymers under poor solvent conditions. Qualitative agreement is reached with some recent experiments.

[120] Nanocomposites by Electrostatic Interactions - 1 - Impact of Sublayer Quality on the Organization of Functionalized Nanoparticles on Charged Self-Assembled LayersF. Auer, M. Scotti, A. Ulman, R. Jordan, B. Sellergren, J. Garno and G. Y. LiuLangmuir 16(20) (2000), 7554-7557

Bis-benzamidines were studied as linkers for the formation of gold nanoparticle assemblies on planar gold surfaces modified with omega-mercaptohexadecanoic acid. In situ ellipsometry, external reflection Fourier transform spectroscopy, and atomic force microscopy showed that the packing density and order of the bis-benzamidine layer exerted a pronounced influence on the thickness and density of the nanoparticle layers. These layers exhibited optical properties similar to those of solid gold.

[121] Selective Self-Organization of Colloids on Patterned Polyelectrolyte Templates


K. M. Chen, X. P. Jiang, L. C. Kimerling and P. T. HammondLangmuir 16(20) (2000), 7825-7834

Submicron-sized colloidal particles have been self-organized into patterned arrangements on a substrate using a novel technique. At the substrate, a polyelectrolyte multilayer film has been deposited onto a chemically patterned surface; subsequently, the polyelectrolyte surface is immersed in an aqueous colloidal suspension of bare SiO2 microspheres or functionalized polystyrene latex particles. The colloids self- organize at the surface, driven by the spatially varied electrostatic and secondary interactions between the colloid and the substrate. The polyelectrolyte platform provides a strong bond to the colloids, imparting mechanical robustness which enables postprocessing of the patterned assemblies. An important advantage to this approach is that the use of a polyelectrolyte multilayer platform opens up the possibility of introducing functionality into the underlying layers. We have demonstrated control over the density and selectivity of particle adsorption. Three mechanisms have been used to control adsorption: (i) pH of the colloid suspension, which determines the ionization of the uppermost surface of the polyelectrolyte multilayer; (ii) ionic strength of the suspension, which determines the extent of charge screening about the colloid and polyelectrolyte; and (iii) concentration of added surfactant, which causes charge screening and introduces hydrophobic interactions between the surfactant and polyelectrolyte. Finally, an energy adsorption model is presented.

[122] Layer-by-Layer Assembly of CdSe Nanoparticles Based on Hydrogen- BondingE. C. Hao and T. Q. LianLangmuir 16(21) (2000), 7879-7881

We report the synthesis of nonaqueous dispersion of CdSe nanoparticles and the layer-by-layer assembly of hybrid poly(vinylpyridine) (PVP)/CdSe multilayer thin films based on hydrogen bonding. The multilayer buildup is monitored by W-vis spectra, which showed a linear increase of the film absorbance with the number of adsorbed CdSe layers. The resulted films have a high degree of flatness and smoothness as indicated by small-angle X-ray diffraction. Hydrogen bond interaction, the driving force for the formation of PVP/CdSe multilayer thin film, between the pyridine group of PVP and the carboxylic acid group on CdSe was verified by FTIR spectroscopy.

[123] Selective Deposition in Layer-by-Layer Assembly - Functional Graft-Copolymers as Molecular TemplatesX. P. Jiang and P. T. HammondLangmuir 16(22) (2000), 8501-8509

A new approach to creating patterned composite structures with layer-by-layer assembled thin films is introduced. In this approach, the top surfaces of layer-by-layer films are chemically patterned by the direct stamping of functional polymers on the surface. The resulting pattern is then used as a template for the further deposition of materials on the surface. This paper illustrates this concept through the patterning of an oligoethylene glycol resist atop a polyelectrolyte multilayer surface. The resist layer is created by stamping an oligoethylene oxide-maleic anhydride graft copolymer onto the top polyamine surface. Further deposition of polyions results in the formation of a patterned polymer film atop the original multilayer thin film. When a patterned polyelectrolyte film is used as the base layer or substrate in this process, a second pattern can be stamped atop the original patterned array. Subsequent selective adsorption of polymers yields a second level of microstructures, illustrating the concept of multiple level patterning for layer-by-layer thin films; this concept can be broadened to include selective deposition of numerous materials on top of multilayer polymer systems.

[124] Design and Demonstration of Hybrid Multilayer Structures - Layer-by-Layer Mixed Covalent and Ionic Interlayer Linking ChemistryP. Kohli and G. J. BlanchardLangmuir 16(22) (2000), 8518-8524

We report on the growth of layered molecular assemblies where the interlayer attachment chemistry is controlled layer-by- layer. We demonstrate the compatibility of chemistry where the layers are connected by ionic coordination chemistry [ROPO32-- Zr4+--O2CR]+OH- and by the formation of covalent urea moieties. A maleimide-vinyl ether (MVE) copolymer containing pendant benzoic acid and butyl alcohol functionalities is used for ionic layer growth. Coupling of covalently bonded adlayers to the MVE polymer is achieved by the attachment of poly(ethylene imine), PEI, to the MVE surface. Subsequent reaction of the PEI surface with diisocyanates and diamines produces urea-linked covalent multilayers. The covalent multilayers can be converted to ionic growth chemistry by treatment of the aminated terminal surface with POCl3 and water followed by further reaction with MVE polymer and Zr4+ ions. We report the reaction schemes for these hybrid layer structures and the characterization of these novel materials by


optical ellipsometry, FTIR and UV-vis spectroscopy, XPS, and X-ray diffraction. The data show the formation of robust multilayer assemblies characterized by limited order within each layer.

[125] Films of Manganese Oxide Nanoparticles with Polycations or Myoglobin from Alternate-Layer AdsorptionY. Lvov, B. Munge, O. Giraldo, I. Ichinose, S. L. Suib and J. F. RuslingLangmuir 16(23) (2000), 8850-8857

Alternate adsorption of manganese oxide nanoparticles with polycations poly(dimethyldiallyl-ammonium) (PDDA) or myoglobin (Mb) onto silver, quartz, and rough pyrolytic graphite gave stable, porous, ultrathin films. Quartz crystal microbalance (QCM) and UV- vis absorbance revealed regular film growth at each adsorption step for MnO2 and PDDA and for SiO2 nanoparticles and Mb. Scanning electron microscopy of MnO2/PDDA films showed smooth surfaces on the 20 nm scale and cross sections consistent with individual nanoparticles. QCM during growth of films of Mb and MnO2 reflected a competition for adsorption of the protein by the film surface and dispersed MnO2 nanoparticles. Nevertheless, films of Mb and MnO2 up to 30 nm thick on rough pyrolytic graphite electrodes could be constructed These novel films featured reversible interconversion of the protein's heme Fe-III/Fe-II redox couple with 10 electroactive layers of protein, considerably more than for polyion-Mb films on smooth gold (ca. 1.3 electroactive layers), and coiled PSS/Mb, films on rough graphite (7 electroactive layers). Shifts in redox potential caused by CO complexation of the heme Fen, BET specific areas, and electrochemically driven catalytic reduction of oxygen suggest that the Mb/MnO2 films are highly porous to gas molecules. To our knowledge, these films represent the first nanofabrication of inorganic particles with functional proteins by the layer-by- layer method.

[126] Steady-State and Time-Resolved Spectroscopy of a Self-Assembled Cyanine Dye MultilayerE. Rousseau, M. Vanderauweraer and F. C. DeschryverLangmuir 16(23) (2000), 8865-8870

Ultrathin organic multilayers, consisting of polyelectrolytes and J-aggregates of a cyanine dye, were obtained using the layer by layer alternate adsorption technique. Buildup of the multilayer is followed by UV-vis absorption spectroscopy. The fluorescence properties of the J-aggregates are studied by steady-state fluorescence spectroscopy and picosecond fluorescence decay measurements. Fluorescence of the cyanine dye, when adsorbed on the substrate, results in a narrow emission band with a small Stokes shift which is characteristic for J-aggregate emission. Time-resolved fluorescence measurements yield a very short average decay time, which can be attributed to the J-aggregates. These results describing the fluorescence properties of multilayer assemblies containing J- aggregates allow on to compare them to those of J-aggregates of the cyanine dye in solution.

[127] Polyelectrolytes I - Polyanion/Polycation Multilayers at the Air/Monolayer/Water Interface as Elements for Quantitative Polymer Adsorption Studies and Preparation of Hetero- Superlattices on Solid-SurfacesJ. Ruths, F. Essler, G. Decher and H. RieglerLangmuir 16(23) (2000), 8871-8878

Polyanion/polycation multilayers floating at the air/water interface were prepared by consecutive adsorption of polyelectrolyte layers onto a Langmuir monolayer from aqueous polyelectrolyte subphase solutions. With the positively charged Langmuir monolayer headgroups of the lipid dimethyldioctadecylammonium bromide, the layer sequence starts with the negatively charged polyelectrolyte polystyrene sulfonate. With the negatively charged monolayer dimyristoylphosphatidic acid, it starts with the positively charged polyallylamine. Equally charged monolayer headgroups and polyelectrolytes do not bind to each other. Consecutive subphase exchange cycles of polyelectrolyte solutions with alternating charges and pure solvent in between lead to the formation of floating multilayers consisting of an alternating polyelectrolyte sequence. Ellipsometric measurements show that the thickness (adsorbed amount per unit area) of the multilayer film at the air/water interface grows in proportion to the number of adsorbed polyelectrolyte layers. The thickness of individual layers increases with increasing polyelectrolyte and/ or ion subphase concentration, respectively. The floating multilayers can be deposited as a sequence of layers of monomeric lipid and polyelectrolytes (hetero-superlattices) onto solid substrates via Langmuir-Blodgett transfer. UV- absorbance studies corroborate the quantitative interpretation of the ellipsometric data in terms of the polymer concentration in the layers, the individual layer thicknesses, and the adsorbed amounts per unit area.

[128] Microencapsulation of Uncharged Low-Molecular-Weight Organic Materials by Polyelectrolyte Multilayer Self-Assembly


F. Caruso, W. J. Yang, D. Trau and R. RennebergLangmuir 16(23) (2000), 8932-8936

Two uncharged microcrystalline substances, pyrene (PYR) and fluorescein diacetate (FDA), were rendered water dispersible by treatment with various amphiphilic substances and subsequently encapsulated by exposure to an alternating sequence of cationic and anionic polyelectrolytes. The amphiphilic compounds employed to charge the microcrystals were ionic surfactants, phospholipids, and polyelectrolytes with an amphiphilic nature. Polyelectrolyte layers were self-assembled onto the pre-charged microcrystalline templates by means of electrostatic layer-by- layer deposition, thus forming a multilayered polymeric shell around the crystalline cores. The semipermeable nature of the polymer multilayer shell was thereafter exploited to remove the templated core by exposure to a mild organic solvent. The release behavior of solubilized PYR and FDA from the crystalline core was examined by monitoring their fluorescence after dissolution with ethanol. Complete removal of the core yielded hollow polymer capsules of micrometer dimensions. The capsule porosity was found to be influenced by the amphiphile used to pre-charge the microcrystal surface. The strategy presented is expected to be a general approach for the encapsulation of hydrophobic, low molecular weight compounds such as drugs, as well as providing a novel and facile pathway to the fabrication of polymer multilayered microcapsules with controlled release properties for drug delivery.

[129] Adsorption-Induced 2nd-Harmonic Generation from the Layer-by- Layer Deposited Ultrathin-Film Based on the Charge-Transfer InteractionY. Shimazaki, S. Ito and N. TsutsumiLangmuir 16(24) (2000), 9478-9482

This paper is concerned with the second harmonic generation (SHG) from as deposited layer-by-layer adsorbed films. A nanolayered film was fabricated through the intermolecular charge-transfer interaction between the electron-donating carbazole (Cz) group and electron-accepting 3,5-dinitrobenzoyl group in the side chains of methacrylate-based polymers. A nonlinear optical dye was introduced in the film by using the copolymer in which Cz and disperse red 1 (DR1) groups were attached to the side chains. The DR1 moiety was highly oriented through the adsorption of PCzEMA-DR1, and the orientation was relaxed by additional adsorption of the polymers onto the DR1- containing layer, The second harmonic (SH! intensity of the multilayered film remained almost constant for the layers of even and odd numbers. This behavior could be explained by considering the change in the nonlinear susceptibility of the succeeding DR1-containing layer. The SH intensity kept constant up to 120 degreesC for thermal stability.

[130] Enzyme Multilayers on Colloid Particles - Assembly, Stability, and Enzymatic-ActivityF. Caruso and C. SchulerLangmuir 16(24) (2000), 9595-9603

Colloidal biocatalysts, comprising polystyrene (PS) carrier particles coated with enzyme multilayers, were fabricated via the layer-by-layer self-assembly method. Glucose oxidase (GOD), horseradish peroxidase (POD), or preformed enzyme- polyelectrolyte complexes were assembled in alternation with oppositely charged polyelectrolytes onto PS particles. Microelectrophoresis, single-particle light scattering, and transmission electron microscopy confirmed stepwise growth of the multilayer films on the colloid particles. The high surface area Enzyme multilayer-coated particles were successfully employed as specific enzyme reactors (i.e., as catalysts). Whereas no loss in activity was observed for the enzymes immobilized directly onto particle surfaces, precomplexing the enzymes with polymer in solution drastically reduced their activity (by up to 70%). The enzymatic activity (per particle) was found to increase with the number of enzyme layers immobilized, irrespective of whether the enzyme was precomplexed. However, particles coated with preformed enzyme- polyelectrolyte complexes displayed a significantly lower enzymatic activity than those fabricated by the direct adsorption of free enzyme. Multicomponent films of GOD and POD on colloid particles were also prepared, and sequential enzymatic catalysis was demonstrated. Furthermore, experiments were conducted with particles exhibiting both magnetic and catalytic functions. These particles, premodified with a layer of magnetic nanoparticles to impart a magnetic property and subsequently coated with enzyme multilayers, were repeatedly used as catalysts following their rapid and easy separation with a magnet. Such biocolloids are expected to find applications in biotechnology.

[131] Layer-by-Layer Self-Assembly of Organic-Organometallic Polymer Electrostatic Superlattices Using Poly(Ferrocenylsilanes)M. Ginzburg, J. Galloro, F. Jakle, K. N. Powerbillard, S. M. Yang, I. Sokolov, C. N. C. Lam, A. W. Neumann, I. Manners and G. A. OzinLangmuir 16(24) (2000), 9609-9614


Water-soluble poly(ferrocenylsilane) (PFS) and poly(styrenesulfonate) (PSS) of alternating charge are shown to self-assemble in a layer-by-layer fashion on primed Au, Si, and quartz substrates to create the first examples of organic- organometallic electrostatic superlattices from polymers with ferrocene units in the backbone. The layer-by-layer assembly of these electrostatic superlattices has been monitored through frequency changes with layer deposition using a quartz-crystal microbalance (QCM), a regular film thickness increase observed using ellipsometry, and step-wise absorbance increases observed using ultraviolet-visible (UV-vis) spectroscopy. As well, structural information was obtained using X-ray photoelectron spectroscopy (XPS), water contact angle measurements, and atomic force microscopy (AFM). These superlattices are of interest as possible precursors to patterned magnetic and redox active multilayers.

[132] Amphoterization of Colloidal Gold Particles by Capping with Valine Molecules and Their Phase-Transfer from Water to Toluene by Electrostatic Coordination with Fatty Amine MoleculesA. Kumar, P. Mukherjee, A. Guha, S. D. Adyantaya, A. B. Mandale, R. Kumar and M. SastryLangmuir 16(25) (2000), 9775-9783

The surface modification of colloidal gold particles with the amino acid valine is demonstrated. Self-assembly of valine on the gold particles is accomplished in the aqueous phase, linkage with the gold particles possibly occurring through covalent interaction of the amine group with the surface gold atoms. Derivatization with the amino acid in this manner imparts amphotericity to the gold particles, the particles being negatively charged at pH values greater than 6 (the isoelectric point of valine) and positively charged below this pH. The charge reversal on the gold particles is demonstrated by electrostatic self-assembly of the colloidal gold particles on glass (which is negatively charged at pH > 3) by immersion of the substrate alternately into the valine-capped gold solutions maintained at pH = 3.5 and 8.5. The phase transfer of the aqueous valine-capped gold colloidal particles by electrostatic linkage with fatty amine molecules present in toluene is also described. The two-phase method described herein is extremely simple and results in hydrophobic gold particles which may be precipitated out of solution and redissolved in different nonpolar organic solvents without significant variation in the particle size distribution. The electrostatically driven multilayer assembly of the valine- derivatized gold particles on glass substrates, the phase transfer process, and the stability of the hydrophobized gold particles have been investigated with a variety of techniques such as UV-vis, infrared and X-ray photoemission spectroscopies, ellipsometry, and thermogravimetry/differential thermal analyses.

[133] Modeling of the Salt Permeability in Fixed Charge Multilayer MembranesK. Lebedev, P. Ramirez, S. Mafe and J. PellicerLangmuir 16(25) (2000), 9941-9943

[134] Sprayed Polyelectrolyte MultilayersJ. B. Schlenoff, S. T. Dubas and T. FarhatLangmuir 16(26) (2000), 9968-9969

Polyelectrolyte multilayers deposited by sequential spraying of poly(styrenesulfonate) and poly(diallyldimethylammonium) solutions are described. A highly uniform thin film is rapidly obtained over a large area. The morphology, uniformity, and chemical composition of sprayed multilayers, as well as the selective membrane properties, are found to be virtually identical to those prepared by dip-immersion.

[135] The Role of Secondary Interactions in Selective Electrostatic Multilayer DepositionS. L. Clark and P. T. HammondLangmuir 16(26) (2000), 10206-10214

Electrostatic layer-by-layer thin films maybe directed to specific regions of a surface based on electrostatics, secondary interactions, and steric repulsion. In this study, a series of polyamines ranging from hydrophobic polyallylammonium hydrochloride (PAH) to hydrophilic linear polyethyleneimine (LPEI) were coadsorbed with poly(acrylic acid) (PAA) onto patterned self-assembled monolayer (SAM) surfaces. When an acid (COOH) and oligoethylene glycol (EG) SAMs are used as the surface template, it was found that the region of preferred deposition for the more hydrophobic polyamine species was generally the EG region at pH 4.8, rather than the partially charged COOH region. The more hydrophilic LPEI species preferred adsorption on the COOH surface. It is proposed that PAH undergoes complexation with the EG surface based on hydrophobic and hydrogen bonding interactions at moderate


pH. On the other hand, the LPEI backbone is hydrated and is thought to undergo large steric repulsion with the EG surface, thus resulting in deposition only on the COOH surface. The region of preferred adsorption also varied with pH, as the hydrogen- bonding interaction of PAA became important at low pH, and electrostatic interactions became the controlling element for selectivity at high pH, when all systems were highly charged. By tuning polyion-surface interactions, the region of polyion deposition can be carefully controlled on patterned chemical surfaces.

[136] Ultrathin-Film Self-Assembly of Hybrid Organic-Inorganic Metal Coordination PolymersH. Byrd, C. E. Holloway, J. Pogue, S. Kircus, R. C. Advincula and W. KnollLangmuir 16(26) (2000), 10322-10328

We have investigated the self-assembly of ultrathin zirconium coordination monomer and polymer films using a layer-by-layer approach. These materials are of great interest for incorporating metal ion (inorganic) moieties in organic (polymer) films with applications ranging from conductors to catalytic materials. The differences between the polymer and monomer assembly from solution are described. These differences were investigated using UV-vis spectroscopy, AFM, and surface plasmon spectroscopy. The differences in orientation, morphology, roughness, and linearity of deposition reflect the conformational limitations of the polymer toward self-assembly. On the other hand, the sequential assembly of the monomer and Zr metal ion indicates the strong coordination between the metal and the organic ligands, resulting in robust homogeneous films.

[137] Thin-Film Optical Sensors Employing Polyelectrolyte AssemblyS. H. Lee, J. Kumar and S. K. TripathyLangmuir 16(26) (2000), 10482-10489

This work describes the development of thin film optical sensors for pH, metal ions (ferric and mercury), and 2,4- dinitrotoluene detection. To fabricate the pH sensor, a fluorescent molecule, 1-hydroxypyren-3,6,8-trisulfonate, was assembled with a polycation by an electrostatic layer-by-layer assembly technique. The fluorescent indicator molecule exhibits distinct and well-defined emission peaks for protonated and deprotonated forms. The relative peak positions and intensity of fluorescence of the protonated and deprotonated forms change in response to pH variations. For metal ion (ferric and mercury) and 2,4-dinitrotoluene sensing, the indicator molecules were covalently incorporated into poly(acrylic acid) and subsequently assembled with a polycation employing electrostatic layer-by-layer assembly. The sensor is based on the fluorescence quenching of indicator molecules by electron transfer from indicator to electron-deficient analytes such as ferric ions, mercury, and 2,4-dinitrotoluene. Fluorescence intensities decreased with increasing concentration of analytes, Quenching behavior follows Stern-Volmer bimolecular quenching kinetics. Linear increase in absorbance, film thickness, and emission intensity was observed as a function of number of bilayers deposited in all these films.

[138] Multilayer Assemblies of Copolymer Psoh and PVP on the Basis of Hydrogen-BondingL. Y. Wang, S. X. Cui, Z. Q. Wang, X. Zhang, M. Jiang, L. F. Chi and H. FuchsLangmuir 16(26) (2000), 10490-10494

An alternating deposition film of a copolymer of p-(hexaflouro- 2-hydroxylisopropyl)-alpha -methylstyrene and styrene (PSOH) and poly(4-vinylpyridine) (PVP) was fabricated on the basis of hydrogen bonding between hydroxyl and a pyridine ring in chloroform. It is found that the selection of solvent is very important for successful preparation of a multilayer film on the basis of hydrogen bonding. A series of PSOHs with different contents of hydrogen-bonding donors were used to fabricate multilayer assemblies. The driving force for multilayer assemblies was identified by FTIR. Several factors, such as solvents, concentration, and content of hydrogen-bonding donors, were discussed, which influence greatly the deposition process and layered architectures.

[139] Preparation of Microcapsules of Strong Polyelectrolyte Couples by One-Step Complex Surface PrecipitationA. Voigt, E. Donath and H. MöhwaldMACROMOL MATER ENG 282(9) (2000), 13-16

Full Paper: Polyelectrolyte microcapsules are fabricated by a one-step surface precipitation and by a layer-by-layer technique an decomposable colloids. The ternary solvent water/ acetone/sodium bromide is adjusted properly keeping dissolved simultaneously the strong polyelectrolytes sodium poly(styrene sulfonate) and poly(vinyl benzyl


trimethylammonium chloride). Microcapsules are characterized by confocal laser scanning microscopy and scanning force microscopy. The capsules are dissolvable in the ternary solvent. Other dissolved strong polyelectrolyte couples and template-free preparation pathways are suggested.

[140] Self-Assembly of Mono-Layer and Multilayer of Polyconjugated Conducting PolymersA. Berlin and G. ZottiMACROMOL RAPID COMMUN 21(7) (2000), 301-318

To obtain organised mono- and multilayers of policonjugated polymers or oligomers by self assembly techniques has recently attracted much attention. This is due to the simplicity of the method and to the fact that no sophisticated apparatus is required. In the present feature the state of the art in this field is discussed including our own research results. A survey on self assembly of thiols, disulfides, and alkylsilanes on gold or glass surfaces is presented as well as self assembly of ferrocenylalkyl-substituted heterocycle adsorbates on ITO surfaces. Carboxyalkyl bithiophenes and terthiophenes, in which the oligothiophene tail is either perpendicularly or linearly linked to the tethering carboxyalkyl chain form stable monolayers on ITO electrodes and are anodically oxidised to produce polymer layers or to couple with oligothiophenes in solution, depending on the structure. As for multilayers, an introductory survey on the self assembly technique usually employed is given. Several examples of multilayers constituted of electroconductive polymers are discussed. Finally our recent results concerning different multilayers from polythiophenes bearing anionic and cationic moieties are discussed.

[141] Ultrathin Polymer-Coatings by Complexation of Polyelectrolytes at Interfaces - Suitable Materials, Structure and PropertiesP. Bertrand, A. Jonas, A. Laschewsky and R. LegrasMACROMOL RAPID COMMUN 21(7) (2000), 319-348

The article presents the state-of-the-art of alternating physisorption of oppositely charged polyelectrolytes, the so- called ''layer-by-layer'' method or ''electrostatic self- assembly'' (ESA), for the preparation of thin polymer coatings. In comparison to other, more established self-organization techniques, this recent method is distinguished by its simplicity, versatility, and speed. In particular, the tendency for self-healing is unique. Emphasis is given to the role of the molecular structure of the polyelectrolytes, and to the nature of the support. Also, various parameters for the preparation of multilayer films are highlighted, which are very important due to the kinetic control of the build-up process. The structure of the resulting coatings, their quality and stability, chemical reactions in the films, and potential applications are discussed.

[142] Preparation of Enzyme Multilayers on Colloids for BiocatalysisC. Schuler and F. CarusoMACROMOL RAPID COMMUN 21(11) (2000), 750-753

Communication: The construction of enzyme multilayer films on colloidal particles for biocatalysis is described. The enzyme multilayers were assembled on submicrometer-sized polystyrene spheres via the alternate adsorption of poly(ethyleneimine) and glucose oxidase using a layer-by-layer approach. Microelectrophoresis and single particle light scattering measurements revealed regular and step-wise assembly of the multilayers on the colloids. The high surface area bio- multilayer coated particles formed were subsequently utilized in enzymatic catalysis.

[143] Synthesis and Electrostatic Multilayer Assembly of an Acridine- Containing Polymer with Properties of an Optical SensorT. S. Lee, C. D. Yang and W. H. ParkMACROMOL RAPID COMMUN 21(14) (2000), 951-955

We have synthesized an acridine-containing polymer linked with alkyl amide via simple polycondensation reaction. It was found that the polymer exhibits high selectivity and sensitivity toward ferric ions indicating that this polymeric material would be an efficient fluorescence sensor for ferric ions. The formation of self-assembled multilayers was carried out via layer-by-layer deposition technique between the acridine- containing polymer and poly(sodium-4-styrenesulfonate).


[144] Layer-by-Layer Adsorption of Identically Charged PolyelectrolytesP. Fischer and A. LaschewskyMacromolecules 33(3) (2000), 1100-1102

[145] PH-Dependent Thickness Behavior of Sequentially Adsorbed Layers of Weak PolyelectrolytesS. S. Shiratori and M. F. RubnerMacromolecules 33(11) (2000), 4213-4219

A detailed study of the role that solution pH plays in the layer-by-layer processing of the weak polyelectrolytes poly(acrylic acid) and poly(allylamine hydrochoride) was carried out. It was found that dramatically different polymer adsorption behavior is observed as one systematically increases (or decreases) the charge density of a weak polyelectrolyte including transitions from very thick adsorbed layers (ca. 80 Angstrom) to very thin adsorbed layers (ca. 4 Angstrom) over a very narrow pH range. By controlling pH, it is possible to vary the thickness of an adsorbed polycation or polyanion layer from 5 to 80 Angstrom. In addition, control over the bulk and surface composition of the resultant multilayer thin films is readily achieved via simple pH adjustments. These studies have provided new insights into the polyelectrolyte sequential adsorption process and have already opened up some interesting technological applications.

[146] Lipid Coating on Polyelectrolyte Surface-Modified Colloidal Particles and Polyelectrolyte CapsulesS. Moya, E. Donath, G. B. Sukhorukov, M. Auch, H. Baumler, H. Lichtenfeld and H. MöhwaldMacromolecules 33(12) (2000), 4538-4544

Dipalmitoyldiphosphatidic acid (DPPA), dipalmitoyldiphosphatidylcholine (DPPC), and sphingosine were adsorbed onto polyelectrolyte coated colloids and capsules forming composite lipid-polyelectrolyte layers. The stepwise coating was performed either by adsorption of preformed vesicles onto the capsule surface or by a solvent exchange protocol. The lipid assembly was monitored by zeta-potential measurements. Single particle light scattering, flow cytometry, and fluorescence studies of Forster energy transfer have been used to quantify the lipid coating. Confocal microscopy images of capsules coated with fluorescent lipids demonstrated a homogeneous coverage of the capsule surface. Differential scanning calorimetry shows a phase transition temperature characteristic for lipid layer structures. It was concluded that the adsorbed DPPA form bilayers while DPPC may form multilayers. It was further shown that on top of the lipid layers further polyelectrolyte layers could be assembled. The permeability of B-carboxyfluorescein (6-CF) through the composite layer structure was studied by means of confocal laser scanning microscopy. The permeation time through the composite layer was of the order of 10(1)-10(2) min, while in the absence of lipids 6-CF equilibrated faster than the time resolution of the technique.

[147] Azo Polymer Multilayer Films by Electrostatic Self-Assembly and Layer-by-Layer Post Azo FunctionalizationS. H. Lee, S. Balasubramanian, D. Y. Kim, N. K. Viswanathan, S. Bian, J. Kumar and S. K. TripathyMacromolecules 33(17) (2000), 6534-6540

This work focuses on the development of a novel method for molecular level assembly and processing of multilayer azo polymer films. Poly(acrylic acid)-based precursor anilino- functional polymer was first synthesized and used as a polyanion. This polymer was assembled into mono- and multilayer thin films by an electrostatic layer-by-layer deposition technique in conjunction with a polycation. The aniline group in the assembled polymer layer was subsequently converted to an azobenzene chromophore by post azo coupling reaction with appropriate diazonium salts. This method provides easy control of film thickness and well-ordered chromophore structure in the multilayer. Second harmonic generation was observed in all multilayer films, indicating acentric organization of the chromophores synthesized in the multilayered films. The second harmonic intensity and film thickness are dependent on the assembly conditions (pH, etc.) of the polyions. The post- functionalized azo polymer layers were further modulated by Light-driven mass transport.

[148] Effects of Spacer Chain Lengths on Layered Nanostructures Assembled with Main-Chain Azobenzene Ionenes and PolyelectrolytesJ. D. Hong, B. D. Jung, C. H. Kim and K. KimMacromolecules 33(21) (2000), 7905-7911


With the aim of fabricating internally ordered multilayer assemblies using the layer-by-layer electrostatic deposition method, we have prepared polyelectrolytes called ionenes that contain rigid azobenzene chromophores separated by flexible spacer chains, i.e., poly ((4,4'-bis(6- dimethylammonio)hexyl)oxy)azobenzene bromide), PAZ-B, poly ((4,4'-bis(10-dimethylammonio)decyl)oxy)azobenzene bromide), PAZ-10, and poly ((4,4'-bis(12- dimethylammonio)dodececyl)oxy)azobenzene bromide), PAZ-12. UV/ vis spectroscopy of solutions shows that PAZ-10 and PAZ-12 form robust lamellar aggregates that could be successfully transferred onto a solid substrate by forming multilayer assemblies with oppositely charged polyelectrolytes, From FTIR spectra of the resulting multilayer assemblies, the alkyl chains appeared to be highly ordered, especially in the case of longer spacer chain. The thicknesses of the PAZ monolayers measured atomic force microscopy were overall consistent with the theoretical values (2.61 and 3.23 nn) determined by a model calculation, based on the tilt angle measurement of chromophore and the molecular length of the repeat unit of the ionenes.

[149] Orientation of Nonlinear-Optical Active Dyes in Electrostatically Self-Assembled Polymer-Films Containing CyclodextrinsP. Fischer, M. Koetse, A. Laschewsky, E. Wischerhoff, L. Jullien, A. Persoons and T. VerbiestMacromolecules 33(26) (2000), 9471-9473

[150] Ultrathin-Film Fabricated from Pddac/DSB and Ndr/DSBJ. Y. Chen, G. B. Luo, R. X. Wang, X. S. Zhao and W. X. CaoMATER RES BULL 35(12) (2000), 1945-1954

Two kinds of ultrathin films were successfully fabricated by the self-assembly deposition technique from poly(diallyldimethylammonium chloride) (PDDAC) or nitro- containing diazoresin (NDR) as the polycation and 4,4'- di(sodium styryl-2-sulfonate) biphenyl (DSB) as the dianion. This stepwise fabrication process was monitored by UV-vis spectrometry. The regularity of the film and the morphology of the film surface were examined by X-ray diffraction (XRD) and atom force microscopy (AFM), respectively. The results show that these kinds of films are composed of well arranged molecules, and have a very flat surface. Among them, the PDDAC/ DSB film emits fluorescence when excited with UV light at 354 nm. The NDR/DSB film does not emit fluorescence, because the NDR quenches the fluorescence of DSB; however, the NDR/DSB film possesses more stability against solvent etching (such as DMF), compared with the PDDAC/DSB film. (C) 2001 Elsevier Science Ltd. All rights reserved.

[151] Ultrathin Nanoparticle ZnS and ZnS Mn Films - Surface Sol-Gel Synthesis, Morphology, Photophysical PropertiesN. I. Kovtyukhova, E. V. Buzaneva, C. C. Waraksa and T. E. MalloukMATER SCI ENG B SOLID STATE M 69(NSI) (2000), 411-417

Ultrathin films of ZnS and Mn-doped ZnS were grown on silicon substrates using surface sol-gel reactions, and the film growth process was characterized by ellipsometry, atomic force microscopy, X-ray photoelectron spectroscopy, UV-visible absorbance and photoluminescence (PL) spectroscopy. The Si substrates were pre-treated by chemical oxidation. On the oxidized Si/SiOx surface, nanoparticulate films of ZnS and Mn- doped ZnS were grown by sequential immersion in aqueous metal acetate and sodium sulfide solutions. During the first four adsorption cycles, there was little film growth, but thereafter the amount of material deposited was linear with the number of adsorption cycles. This behavior is consistent with the formation of ZnS nuclei at low coverage, followed by particle growth in subsequent cycles. PL spectra are consistent with incorporation of Mn2+ into the ZnS nanoparticles. (C) 2000 Elsevier Science S.A. All rights reserved.

[152] Self-Assembly of Nanostructured Composite ZnO/Polyaniline FilmsN. I. Kovtyukhova, A. D. Gorchinskiy and C. WaraksaMATER SCI ENG B SOLID STATE M 69(NSI) (2000), 424-430

Ultrathin composite ZnO/polyaniline (PAN) films were deposited from organic solutions on silicon and ITO substrates using wet layer-by-layer self-assembly technique. The film growth process was characterized by transmission electron microscopy, ellipsometry, atomic force microscopy, IR and UV-visible absorbance and photoluminescence spectroscopy, and electrical measurements. The Si substrates were pre-treated by chemical oxidation. Multilayer films were grown by sequential immersion of the substrate in an ethanolic ZnO sol and PAN solution in dimethyl formamide. The first adsorption cycle resulted in well- packed monoparticulate ZnO layer almost


completely covering the substrate, which predetermined the regular growth of densely packed and quite smooth ten-layer ZnO/PAN film. Photoluminescence and IR data assumed chemical interaction between the components in neighbouring layers. The multilayer (ZnO/PAN)(9)ZnO film sandwiched between ITO and Pr electrodes exhibited strong photoelectrical response while both the components were photoelectrically inactive in our experimental conditions. The reversible conversion from insulating to conducting state was observed under irradiation by light with a wavelength below 350 nm. (C) 2000 Elsevier Science S.A. All rights reserved.

[153] Photoinduced Alignments of Liquid-Crystal Molecules on Alternate Self-Assembly Films Evaluated by the Attenuated Total- Reflection MeasurementA. Baba, F. Kaneko, K. Shinbo, K. Kato, S. Kobayashi and R. C. AdvinculaMOL CRYST LIQUID CRYST 347 (2000), 259-268

Photo-induced in-plane alignments of nematic liquid crystal (LC) molecules, 5CB, have been investigated in the cell with alternate self-assembly films of polyelectrolyte and low- molecular weight dyes on the gold electrodes using the attenuated total reflection (ATR) measurement method. Reflectivities due to the excitations of the surface plasmon polariton (SPP) were observed in the ATR properties of the LC cell. In-plane switching of LC molecules adjacent to the aligning layer was evaluated from the ATR curves by means of irradiation of the linearly polarized visible light to the LC cell. It was also estimated that the re-orientation of the LC molecules occurred within about 130 nm from the surface of the aligning layer on the prism by the irradiation of the polarized light.

[154] Rectifying Self-Assembled Ultrathin FilmsT. P. Cassagneau, B. Swerydakrawiec and J. H. FendlerMRS BULL 25(9) (2000), 40-46

[155] Nanoassemblies of Sulfonated Polyaniline MultilayersN. Sarkar, M. K. Ram, A. Sarkar, R. Narizzano, S. Paddeu and C. NicoliniNANOTECHNOL 11(1) (2000), 30-36

A self-assembly layer-by-layer (LBL) technique was used for the sequential adsorption of polycation, poly(diallyldimethylammonium chloride) (PDDA) and polyanion, sulfonated polyaniline (SPANI) on glass. indium-tin-oxide (ITO) coated grass plates, polystyrene sulfonate (PSS)/glass and PSS/ ITO surfaces, respectively The building up of such multilayers was characterized by the increment of the: adsorbed amount through UV-visible spectroscopy and cyclic voltammetry The atomic force microscopic study showed the granular surface topology of such self-assembled films of sulfonated polyaniline. PDDA/SPANI LBL films were electrically active and detailed electrochemical parameters were investigated.

[156] Nano-Assembly of Glucose-Oxidase on the in-Situ Self-Assembled Films of Polypyrrole and Its Optical, Surface and Electrochemical CharacterizationsM. K. Ram, M. Adami, S. Paddeu and C. NicoliniNANOTECHNOL 11(2) (2000), 112-119

An in situ self-assembly technique with nanometre control over thicknesses and multilayered structures was used to manufacture the ultrathin films of polypyrrole (PPY). The PPY film was deposited on a polyanion, poly(styrene sulfonate) (PSS) modified surface as a Function of time, previously PSS had been deposited on various substrates (glass, mica, indium-tin-oxide coated glass plates). Later, alternate PPY and PSS films were fabricated on such substrates using a layer-by-layer (LBL) technique. The glucose oxidase (GOD) molecules were also deposited on such self-assembled PPY films by the LBL technique. The PSS/PPY/GOD, PPY/PPY/GOD/poly(ethylene imine) (PEI)/GOD etc, film configurations were fabricated. and functionally as well as structurally characterized by UV- visible, electrochemical and scanning probe microscopy techniques, respectively. The results of a scanning probe microscopic study on the films were analysed to understand the molecular orientation of GOD on the PPY surface, and the dependence of the enzyme concentration for the depositing solutions. Moreover, the electrochemical studies performed provided information with respect to the electron transfer processes on the spatial arrangement of GOD molecules on the PPY surfaces. The immobilization of GOD on a conductive PPY represented a crucial and important step, and allowed us to construct the glucose-responsive biosensors.


[157] Molecular-Scale Interface Engineering for Polymer Light- Emitting-DiodesP. K. H. Ho, J. S. Kim, J. H. Burroughes, H. Becker, S. F. Y. Li, T. M. Brown, F. Cacialli and R. H. FriendNature 404(6777) (2000), 481-484

Achieving balanced electron-hole injection and perfect recombination of the charge carriers is central to the design of efficient polymer light-emitting diodes(1,2) (LEDs). A number of approaches have focused on modification of the injection contacts, for example by incorporating an additional conducting-polymer layer at the indium-tin oxide (ITO) anode(3,4). Recently, the layer-by-layer polyelectrolyte deposition route has been developed for the fabrication of ultrathin polymer layers(5,6). Using this route, we previously incorporated ultrathin (<100 Angstrom) charge-injection interfacial layers in polymer LEDs(7). Here we show how molecular-scale engineering of these interlayers to form stepped and graded electronic profiles can lead to remarkably efficient singlelayer polymer LEDs. These devices exhibit nearly balanced injection, near-perfect recombination, and greatly reduced pre-turn-on leakage currents. A green-emitting LED comprising a poly(p-phenylene vinylene) derivative sandwiched between a calcium cathode and the modified ITO anode yields an external forward efficiency of 6.0 per cent (estimated internal efficiency, 15-20 per cent) at a luminance of 1,600 candelas per m(2) at 5 V.

[158] Electrooptic Property Measurements of Electrostatically Self- Assembled Ultrathin FilmsL. M. Zhang, F. J. Zhang, K. Cooper, Y. Q. Wang, Y. J. Liu and R. ClausOpt. Commun. 186(1-3) (2000), 135-141

A new class of ultrathin electro-optic films have been developed by the electrostatically self-assembled monolayer process. Using a simple ellipsometric technique, the electro- optic coefficients were measured as a function of the frequency of the applied electric field. The maximum of the coefficients is 600 pm/V. From these measurements, we deduce the orientational and the electronic contributions to the electro- optic modulation. At modulating frequencies lower than 20 Hz, the orientation dominates the electro-optic modulation process. At frequencies higher than 800 Hz, electrons are responsible for electro-optic behavior. (C) 2000 Elsevier Science B.V. All rights reserved.

[159] The Influence of Molecular-Weight over the Ultrathin Films of Biodegradable Polyion Complexes Between Chitosan and Poly(Gamma- Glutamic Acid)W. Tachaboonyakiat, T. Serizawa, T. Endo and M. AkashiPolym. J. 32(6) (2000), 481-485

Alternate adsorption is a well-known method for developing the novel. ultrathin films of biodegradable polyion complexes. This study revealed variations in the effect of chitosan and poly(gamma-glutamic acid) [gamma-PGA] molecular weight on the complex formation process. High molecular weight gamma-PGA showed a high adsorption frequency. Tn contrast, no molecular weight effect was observed in the case of chitosan. Addition of certain organic solvents in the chitosan and gamma-PGA aqueous solution also influenced ultrathin film polyion complex formation.

[160] Physical Insight in the in-Situ Self-Assembled Films of PolypyrroleM. K. Ram, M. Adami, P. Faraci and C. NicoliniPolymer 41(20) (2000), 7499-7509

The ultrathin films with nanometre control over thickness and multilayered structures of polypyrrole (PPY) were manufactured by in-situ self-assembled technique. A controlled thickness of PPY was deposited on polyanion, poly(styrene sulfonate) (PSS) surfaces as a function of time; previously PSS had been deposited on various substrates (glass, mica, indium-tin-oxide coated glass plates). Later, alternate PPY and PSS films were fabricated on such substrates by the layer-by-layer technique. The films were characterized by using UV-visible, electrochemical and Quartz Crystal Microbalance techniques. The resulting morphology of the manufactured films was investigated by Atomic Force and the Scanning Tunneling Microscopies. The electrochemical surveying of self-assembled PPY films in different electrolytic media highlighted the sensor application. Typical supramolecular films of PPY/PSS were found to have conductivity values in the range of 10(-2)-10(-1) S/cm. (C) 2000 Elsevier Science Ltd. All rights reserved.

[161] Polymeric Nanostructured Composite Films


J. C. Shen, J. Q. Sun and X. ZhangPure Appl. Chem. 72(1-2) (2000), 147-155

This research news describes the construction of polymeric nanostructured composite film based on a variety of interactions, such as hydrophobic-hydrophilic effect, electrostatic interaction, hydrogen bonding, etc. The work focused on developing strategies to solve the basic problems in the area of ultrathin film research, such as stability, improving the interface quality, creating patterned interface, and techniques to construct nanolayered structure. With in- depth study of the relationship between the microscopic layered architecture and macroscopic function of supramolecular assemblies, it is anticipated that one could obtain miniature devices or machines of high efficiency through integration of the assembling process and device fabrication.

[162] Preparation of DNA-Cationic Amphiphile Multilayer Films by Alternate Adsorption and a Study of Their StructureL. I. Shabarchina, M. M. Montrel, G. B. Sukhorukov, I. V. Savintsev and B. I. SukhorukovRussian J. Phys. Chem. 74(11) (2000), 1908-1914

DNA-hexadecylamine and DNA-hexadecyltrimethylammonium bromide multilayer films were produced by alternate adsorption of DNA and a cationic amphiphile on a solid support. The growth of the film was studied by UV spectroscopy The interlayer distances, DNA conformational states, and hydration and stability of the films in aqueous and aqueous-salt solutions were determined by small-angle X-ray scattering and IR and UV spectroscopies. The structures of the films were proposed. It was shown that the DNA double helix is unwound during the formation of the hexadecylamine multilayer film. In the case of hexadecyltrimethylammonium, the DNA double helix retains the B- form, but its lability diminishes; no transition into the A- form occurs with decreasing humidity. As for hexadecylamine, the influence of the polar head of the amphiphile molecule on the DNA conformational state occurs because of the substitution of base-base intramolecular hydrogen bonds by base- hexadecylamine intermolecular hydrogen bonds. Multilayer films containing the same components but prepared under different conditions (Langmuir process or alternate adsorption of the components on the support) were found to differ in structure.

[163] Self-Assembly of Polyaniline Ultrathin Films Based on Doping- Induced Deposition Effect and Applications for Chemical SensorsD. Li, Y. D. Jiang, Z. M. Wu, X. D. Chen and Y. R. LiSENSOR ACTUATOR B CHEM 66(1-3) (2000), 125-127

Electroactive nanocomposite ultrathin films of polyaniline (PAN) and isopolymolybdic acid (PMA) were fabricated by a novel molecular self-assembling process based on the alternate deposition of PAN and PMA from their dilute solutions. The process was based on doping-induced deposition effect of emeraldine base. The process was monitored by UV/VIS spectroscopy measurement. It was found that the conductivity of the PAN films is sensitive to humidity, NO2 and NH3. The technique may be used to fabricate chemical sensors and other molecular devices. (C) 2000 Elsevier Science S.A. All rights reserved.

[164] Fabrication of Self-Assembled Polyaniline Films by Doping- Induced DepositionD. Li, Y. D. Jiang, Z. M. Wu, X. D. Chen and Y. R. LiThin Solid Films 360(1-2) (2000), 24-27

The ultrathin films of polyaniline (PAni)/poly (styrenesulfonic acid)(PSSA) were fabricated via a novel self-assembling process by alternately immersing the substrates into dilute PAni solution in N-methylpyrrolidinone (NMP) and the aqueous solution of PSSA. The process was characterized by W-Vis absorption spectroscopy. It was found that the oxidation state of polyaniline in single monolayers was dependent on the thickness of the film. The self-assembling mechanism was based on the acid-base reaction between PAni and PSSA. The thickness of the films can be easily manipulated at nanometer scale by controlling the solution chemistry and recycling times. The resulting films are uniform and adhere strongly to the substrates. (C) 2000 Elsevier Science S.A. All rights reserved.

[165] Electrostatic Self-Assembly of Sulfonated C-60-Porphyrin Complexes on Chitosan Thin-FilmsH. Jiang, W. Su, J. Hazel, J. T. Grant, V. V. Tsukruk, T. M. Cooper and T. J. BunningThin Solid Films 372(1-2) (2000), 85-93


Sulfonatcd C-60, 5,10,15,20-tetra kis 4-[meso-tetra-methyl (4- pyridinyl)] porphyrin (C-60(SO3-)(n)-TMePyP4+) complex films have been prepared by electrostatic self-assembly of each chromophore from solution. When these complex films are formed on a thin film of chitosan polymer, the stacked bilayer films exhibit nearly twice the absorption as those prepared on conventional silanized substrates. X-ray photoelectron spectroscopy measurements disclose a strong interaction between the C-60(SO3-)(n) and TMePyP4+. Atomic force microscopy results of the surface morphology, hardness, and the chemical functionality are used to explain the differences between substrate treatments. (C) 2000 Elsevier Science S.A. All rights reserved.

[166] Effect of Added Ionic Salt on the Quantum Efficiency of Self- Assembled Films Prepared with Poly( P-Phenylene Vinylene)J. Cho, K. Char, S. Y. Kim, J. D. Hong, S. K. Lee and D. Y. KimThin Solid Films 379(1-2) (2000), 188-194

Multilayer electroluminescence (EL) devices based on the self- assembled layers of poly(p-phenylene vinylene) (PPV) and poly(sodium 4-styrenesulfonate) (PSS) were prepared and characterized. The increase of recombination region for the radiative decay of polaron excitons in the film device was achieved by two different fabrication methods: increase of the number of bilayers and increase of ionic strength of PSS solution using a salt additive. When simply increasing the number of bilayers, the relative device efficiency was improved proportional to the number of bilayers deposited. In contrast, the addition of NaCl salt to the PSS dipping solution resulted in higher thickness deposition but exhibited low luminescence level as well as low quantum efficiency. We believe that the decrease of the quantum efficiency, despite the increased thickness in the case of added salt in the PSS solution, is caused by the defect formation at the interface between PPV/PSS film and Al electrode. In order to minimize this problem, we inserted one insulating bilayer composed of cationic poly(allylamine hydrochloride) (PAH) and anionic poly(methacrylic acid) (PMA) in direct contact with the Al electrode. Upon this insertion, significant improvement of device efficiency was achieved and the quantum efficiency was shown to be proportional to the total film thickness even in the case of the salt addition scheme. (C) 2000 Elsevier Science B.V. All rights reserved.

[167] Electrostatically Self-Assembled Poly(4-Vinylpyridine-Co- Vinylpyridinium-Chloride)-Based LedH. Hong, R. Sfez, E. Vaganova, S. Yitzchaik and D. DavidovThin Solid Films 366(1-2) (2000), 260-264

We demonstrate the fabrication and characterization of an organic light-emitting diode (OLED) device based on self- assembled poly(4-vinyl-pyridine) (P4VPy) with poly(N-vinyl- carbazole) (PVK) and 2-(4-biphenylyl)-5-(4-tert-butyphenyl)- 1,3,4-oxidiazole (PBD) as transport layers. The self-assembly is based on the electrostatic attraction of oppositely-charged polymers. We have shown here that we can use this self- assembled methodology to fabricate alternating multilayers, not only by the poly(phenyl-vinylene) (PPV) and derivatives, but also by partial protonation of P4VPy, by which the charge on P4VPy is generated by the protonation process. The multilayered structures are characterized by specular X-ray reflectivity (XRR), UV absorption, photoluminescence (PL) and electroluminescence (EL). (C) 2000 Published by Elsevier Science S.A. All rights reserved.

[168] Nanoengineering of Particle SurfacesF. CarusoAdv. Mater. 13(1) (2001), 11

The creation of core-shell particles is attracting a great deal of interest because of the diverse applicability of these colloidal particles; e.g., as building blocks for photonic crystals, in multienzyme biocatalysis, and in drug delivery. This review presents the state-of-the-art in strategies for engineering particle surfaces, such as the layer-by-layer deposition process (see Figure), which allows fine control over shell thickness and composition. (See also cover).

[169] Antireflection Surface with Particle Coating Deposited by Electrostatic AttractionH. HattoriAdv. Mater. 13(1) (2001), 51


Single-layer particulate coatings with special anti-reflection (AR) properties were deposited by an electrostatic attraction between the negatively charged colloidal particles and the positively charged surface of polyelectrolyte multilayers (see Figure). It is shown that the AR properties of the coating depend on the number of sequential depositions as well as on the treatment of the particles after deposition.

[170] Hollow Titania Spheres from Layered Precursor Deposition on Sacrificial Colloidal Core ParticlesF. Caruso, X. Y. Shi, R. A. Caruso and A. SushaAdv. Mater. 13(10) (2001), 740-744

[171] The Sense of Chromophore Orientation in Films Made by Alternating Polyelectrolyte DepositionW. N. Herman and M. J. RobertsAdv. Mater. 13(10) (2001), 744-746

[172] Layer-by-Layer Self-Assembly of Glucose-Oxidase and Os(bpy)(2)Cipych2Nh-Poly(Allylamine) BioelectrodeE. J. Calvo, R. Etchenique, L. Pietrasanta, A. Wolosiuk and C. DanilowiczAnal. Chem. 73(6) (2001), 1161-1168

The uptake of glucose oxidase (GOx) onto a polycationic redox polymer (PAA- Os)-modified surface, by adsorption from dilute aqueous GOx solutions, was followed by the quartz crystal microbalance (QCM) and shows double exponential kinetics. The electrochemistry of the layer-by-layer-deposited redox-active polymer was followed by cyclic voltammetry in glucose-free solutions, and the enzyme, catalysis mediated by the redox polymer was studied in P-D-glucose-containing solutions. AFM studies of the different layers showed the existence of large two dimension enzyme aggregates on the osmium polymer for 1 muM GOx and less aggregation for 50 nM GOx solutions. When the short alkanethiol, 2,2'-diaminoethyldisulfide was preadsorbed onto gold, a monoexponential adsorption law was observed, and single GOx enzyme molecules could be seen on the surface where the enzyme was adsorbed from 50 nM GOx in water.

[173] DNA-Mediated Electrostatic Assembly of Gold Nanoparticles into Linear Arrays by a Simple Drop-Coating ProcedureM. Sastry, A. Kumar, S. Datar, C. V. Dharmadhikari and K. N. GaneshAppl. Phys. Lett. 78(19) (2001), 2943-2945

The assembly of nanoparticles in topologically predefined superstructures is an important problem in the area of nanoscale architecture. In this letter, we demonstrate the electrostatic assembly of lysine-capped colloidal gold particles on drop-coated DNA films. Electrostatic interaction between the positive charges on the gold nanoparticles and the negative charges on the phosphate groups of the DNA template molecules leads to the assembly of the gold nanoparticles in linear superstructures. The use of DNA as templates for the assembly of nanoparticles shows promise for extension to more complex geometries through rational design of the DNA base sequences as well as in the realization of nanowires by stringing together metal nanoparticles. (C) 2001 American Institute of Physics.

[174] Charge-Dependent Sidedness of Cytochrome-P450 Forms Studied by Quartz-Crystal Microbalance and Atomic-Force MicroscopyJ. B. Schenkman, I. Jansson, Y. Lvov, J. F. Rusling, S. Boussaad and N. J. TaoArch. Biochem. Biophys. 385(1) (2001), 78-87

Quartz crystal microbalance (QCM) resonance measurements were used to examine the surface charge characteristics of cytochrome P450 forms and the influence of charge on the docking of redox partners like cytochrome b(5). The distal surface of cytochrome P450 (CYP)101 (pI = 4.5), relative to the heme, is fairly anionic, as is the proximal surface. The latter, however, also has two cationic clusters. A considerably greater extent of CYP101 binding was seen to the cationic, polyethylene-surfaced resonators. CYP2B4 (pI = 8.5) preferentially bound to the polyanionic, polystyrene sulfonate- surfaced resonators. Cytochrome b(5) is an acidic protein that had a preferential binding to the poly(ethyleneimine (PEI)- surfaced resonators. When binding to CYP2B4-surfaced films, cytochrome b(5) preferentially bound to those cytochrome P450 molecules that were adsorbed to cationic (PEI) films. It is suggested


that adsorption of CYP2B4 to an anionic poly(styrenesulfonate) (PSS) surface is with cationic clusters that include the cytochrome b(5) docking domain. This diminishes the extent of docking of the cytochrome b(5). In contrast, when CYP2B4 is adsorbed to a cationic film the proximal surface with the cytochrome b(5)-docking site is available for cytochrome b(5) binding. A film of the polycation PEI was adsorbed to the silver QCM surface. It formed polymer islands when viewed with atomic force microscopy. Polyanionic PSS was adsorbed intermittently with the PEI. By the third and fourth layer of polyions the polymer islands were essentially merged and protein adsorption as a fourth or fifth layer formed a nearly continuous film. CYP101 was seen to adsorb as globules with a molecular diameter of about 10 nm. CYP2B4 adsorbed to the polyionic films had a slightly elliptical globular shape, also with a molecular diameter of about 10 nm. (C) 2001 Academic Press.

[175] Direct Electrochemistry of Hemoglobin in Layer-by-Layer Films with Poly(Vinyl Sulfonate) Grown on Pyrolytic-Graphite ElectrodesL. W. Wang and N. F. HuBioelectrochem. 53(2) (2001), 205-212

Stable layer-by-layer electroactive films were grown on pyrolytic graphite (PG) electrodes by alternate adsorption of layers of polyanionic poly(vinyl sulfonate) (PVS) and positively charged hemoglobin (Hb) from their aqueous solutions. Cyclic voltammetry (CV) of {PVS/Hb}(n) films showed a pair of well-defined and nearly reversible peaks at about - 0.28 V vs. SCE at pH 5.5, characteristic of Hb heme Fe(III)/ Fe(II) redox couple. The process of {PVS/Hb} bilayer growth was monitored and confirmed by CV, X-ray photoelectron spectroscopy (XPS) and UV-Vis spectroscopy. While the amount of Hb adsorbed in each bilayer was the same, the amount of electroactive Hb in each bilayer decreased dramatically with increase of the number of bilayer, and electroactivity was just extended to 8 {PVS/Hb} bilayers. CVs of {PVS/Hb}(8) films maintained stable in buffers containing no Hb. Positions of Soret band of Hb in {PVS/Hb}(n) films grown on transparent glass slides suggest that Hb in the films keeps its secondary structure similar to its native state in a wide pH range. Trichloroacetic acid and nitrite were catalytically reduced by (PVS/Hb), films with significant lowering of the electrode potential required. (C) 2001 Elsevier Science B.V. All rights reserved.

[176] Multilayer Capsules - A Promising Microencapsulation System for Transplantation of Pancreatic-IsletsS. Schneider, P. J. Feilen, V. Slotty, D. Kampfner, S. Preuss, S. Berger, J. Beyer and R. PommersheimBiomaterials 22(14) (2001), 1961-1970

In 1980, Lim and Sun introduced a microcapsule coated with an alginate/polylysine complex for encapsulation of pancreatic islets. Characteristic to this type of capsule is, that it consists of a plain membrane which is formed during a single procedural step. With such a simple process it is difficult to obtain instantly a membrane optimized with respect to all the properties requested for islet transplantation. To overcome these difficulties, it is recommended to build up the membrane in several consecutive steps, each optimized for a certain property. In this study, we have analysed such a multilayer microcapsule for the encapsulation of pancreatic islets. Therefore, empty and islet containing alginate beads were coated with alternating layers of polyethyleneimine, polyacrylacid or caboxymethylcellulose and alginate. By scanning electron microscopy the thickness of the covering multilayer-membrane was estimated to be less than 800 nm by comparison with an apparatus scale. Ellipsometric measurements showed that the membrane thickness is in the range of 145 nm. Neither the encapsulation procedure, nor the membrane-forming step did impede the stimulatory response of the islets. The encapsulation even lead to a significantly better stimulatory response of the encapsulated islets during week three and five of cell culture. Furthermore, the multilayer-membrane did not deteriorate the biocompatibility of the transplanted microcapsules. allowing an easy tuning of the molecular cut-off and the mechanical stability depending on the polycation- polyanion combination used. The multilayer membrane capsule has obvious advantages compared to a one-step encapsulation procedure. These beads guarantee a high biocompatibility, a precisely adjusted cut-off, an optimal insulin-response and high mechanical stability although the membrane is only 145 nm thick. (C) 2001 Elsevier Science Ltd. All rights reserved.

[177] Microgravimetric DNA Sensor-Based on Quartz-Crystal Microbalance - Comparison of Oligonucleotide Immobilization Methods and the Application in Genetic DiagnosisX. C. Zhou, L. Q. Huang and S. F. Y. LiBiosensors and Bioelectronics 16(1-2) (2001), 85-95

We report on the study of immobilization DNA probes onto quartz crystal oscillators by self-assembly technique to form variety types of mono- and multi-layered sensing films towards the realization of DNA diagnostic devices. A 18-mer DNA probe complementary to the site of genetic beta -thalassaemia mutations was immobilized on the electrodes


of QCM by covalent bonding or electrostatic adsorption on polyelectrolyte films to form mono- or multi-layered sensing films by self-assembled process. Hybridization was induced by exposure of the QCMs immobilized with DNA probe to a test solution containing the target nucleic acid sequences. The kinetics of DNA probe immobilization and hybridization with the fabricated DNA sensors were studied via in-situ frequency changes. The characteristics of QCM sensors containing mono- or multilayered DNA probe constructed by direct chemical bonding, avidin-biotin interaction or electrostatic adsorption on polyelectrolyte films were compared. Results indicated that the DNA sensing films fabricated by immobilization of biotinylated DNA probe to avidin provide fast sensor response and high hybridization efficiencies. The effects of ionic strength of the buffer solution and the concentration of target nucleic acid used in hybridization were also studied. The fabricated DNA biosensor was used to detect a set of real samples. We conclude that the microgravimetric DNA sensor with its direct detection of amplified products provide a rapid, low cost and convenient diagnostic method for genetic disease. (C) 2001 Elsevier Science B.V. All rights reserved.

[178] Fabrication of Heterogeneous Macroporous Materials Based on a Sequential Electrostatic Deposition ProcessD. Y. Wang and F. CarusoJ. Chem. Soc., Chem. Commun. Iss 5 (2001), 489-490

Heterogeneous macroporous materials are prepared by the sequential electrostatic deposition of fluorescein isothiocyanate-labeled poly(allylamine hydrochloride) and cadmium telluride nanocrystals onto macroporous titania structures.

[179] Self-Assembly of Photo-Responsive Azo PolyelectrolytesX. L. Tuo, Z. Chen, L. F. Wu, X. G. Wang and D. S. LiuCHEM J CHINESE UNIV CHINESE 22(2) (2001), 329-333

Three azo polyelectrolytes were successfully fabricated into self-assembled multilayers through a layer-by-layer dipping technique, The surface morphology and its variation with the bilayer growth were investigated with atomic force microscopy(AFM). The cis-trans isomerization of the self- assembled thin films was studied with UV-Vis spectroscopy and compared with the spin-coated films, PEAPE/PDAC and PPAPE/PDAC multilayers show significant photochromic effect upon UV light irradiation. In dark condition, the rates of cis-to-trans isomerization depend on the chromophore structure. For polyelectrolytes containing the same chromophores, the azo dyes in self-assembled multilayer recover much faster from cis to trans isomer than those in spin-coated films.

[180] Multiple Adsorption of Polythiophene Layers on Ito/Glass Electrodes and Their Optical, Electrochemical, and Conductive PropertiesG. Zotti, S. Zecchin, A. Berlin, G. Schiavon and G. GiroChem. Mater. 13(1) (2001), 43-52

Polyelectrolyte multilayers containing electrochemically active polythiophenes have been constructed on ITO/glass substrates using the layer-by-layer adsorption deposition technique. Electrochemically active layers of poly(cyclopentadithienyl- alkylsulfonate) poly(cyclopentadithienyl-alkylammonium), and alpha,omega -bis(carboxyhexyl)sexithiophene were deposited with non-electroactive layers of polyallylamine and polystyrenesulfonate. The first sequential adsorption of multilayers in which both the polycation and the polyanion are based on the same polythiophene is reported. UV-vis spectroscopy and cyclic voltammetry indicate a linear dependence of the amount of deposited polymer on the number of deposition cycles. The rate of deposition depends on the oxidation state of the polythiophene being 3 times lower for the oxidized polycationic polymer. Atomic force microscopy characterization of the layers has shown that flat monolayers are deposited with a progressive increase of roughness. Interposition of multiple nonelectroactive layers between the electrode and a single external electroactive polythiophene layer has allowed determination by cyclic voltammetry that each polythiophene layer interpenetrates the confining layers up to a three-layer distance. The conductivities of the multilayers along the surface and perpendicular to it are anisotropic depending on the layer alternation. The photoluminescence properties of the alpha,omega -bis(carboxyhexyl)sexithiophene multilayers are the same for vacuum-deposited polycrystalline layers.

[181] Magnetic Nanocomposite Particles and Hollow Spheres Constructed by a Sequential Layering ApproachF. Caruso, M. Spasova, A. Susha, M. Giersig and R. A. CarusoChem. Mater. 13(1) (2001), 109-116


The fabrication of magnetic composite core-shell particles and hollow spheres with tailored dimensions and compositions has been accomplished by a multistep (layer-by-layer) strategy. Composite particles were prepared by coating submicrometer- sized anionic polystyrene (PS) latices with magnetite (Fe3O4) nanoparticle layers alternately adsorbed with polyelectrolyte from aqueous solution. The thickness of the deposited multilayers could be finely tuned with nanoscale precision, either by selection of the number of adsorption cycles performed or by the number of polyelectrolyte layers deposited between each nanoparticle layer (i.e., interlayer). As demonstrated by transmission electron microscopy, a marked improvement in the growth, uniformity, and regularity of the composite multilayers was achieved when the number of polyelectrolyte interlayers was increased from one [(poly(diallyldimethylammonium chloride) (PDADMAC)] to three [(PDADMAC/poly(styrenesulfonate) (PSS)/PDADMAC)]. Hollow, intact magnetic spheres were obtained by calcination of the core-shell particles at elevated temperature. Furthermore, composite hollow spheres were prepared by calcination of PS latices coated with multilayers of silica and Fe3O4 nanoparticles. These nanoengineered colloidal particles may potentially find applications as delivery systems, or in diagnostics, where the particles can be directed by application of an external magnetic field.

[182] Layered Aluminosilicate/Chromophore Nanocomposites and Their Electrostatic Layer-by-Layer AssemblyD. W. Kim, A. Blumstein, J. Kumar and S. K. TripathyChem. Mater. 13(2) (2001), 243-246

[183] Synthesis of Macroporous Titania and Inorganic Composite- Materials from Coated Colloidal Spheres - A Novel Route to Tune Pore MorphologyD. Y. Wang, R. A. Caruso and F. CarusoChem. Mater. 13(2) (2001), 364-371

A new method for fabricating macroporous inorganic and inorganic composite materials with tailored pore morphologies (i.e., pore wall thickness and open or closed pore structure) is described. Polystyrene (PS) colloidal spheres coated with polyelectrolyte (PE) multilayers (PS-PE) or silica nanoparticle (SiO2)/PE hybrid multilayers (PS-SiO2/PE) have been used as templates to produce macroporous structures. By infiltration of a titanium dioxide (TiO2) precursor, titanium (IV) isopropoxide, into templates of close-packed coated colloidal spheres, followed by removal of the organic material (PS core and PE layers) by calcination, macroporous TiO2 and inorganic composite structures were produced. The pore morphology of the resulting macroporous structures depends on the nature of the multilayers deposited on the colloidal spheres. Open pore structures were obtained by templating close-packed assemblies of PS-PE colloidal spheres, while a closed pore structure was achieved by templating PS-SiO2/PE particle assemblies. The wall thickness of the resulting pores can also be tuned by altering the number of multilayers deposited on the colloidal spheres. Increasing the number of multilayers on the spheres causes an increase in the wall thickness of the macroporous structures.

[184] Multilayered Titania, Silica, and Laponite Nanoparticle Coatings on Polystyrene Colloidal Templates and Resulting Inorganic Hollow SpheresR. A. Caruso, A. Susha and F. CarusoChem. Mater. 13(2) (2001), 400-409

The applicability of the layer-by-layer (LbL) technique for the formation of a range of polymer-core inorganic-shell particles and inorganic hollow spheres is demonstrated. Titanium dioxide, silica, and Laponite nanoparticles were used as the inorganic building blocks for multilayer formation on polystyrene (PS) sphere templates. Composite organic-inorganic particles were formed by the controlled assembly of the preformed nanoparticles in alternation with oppositely charged polyelectrolytes onto PS microspheres. The influence of nanoparticle type, shape (spherical to sheetlike), and size (3- 100 nm), and the diameter of the PS sphere templates (210-640 nm) on the formation of multilayer shells was examined by transmission and scanning electron microscopy. In addition, the LbL technique for coating polymer spheres has been shown to be adaptable with small variations in the coating steps used to optimize the nanoparticle coatings of the different materials. For example, the number of polyelectrolyte multilayers separating the nanoparticle layers, and the number of nanoparticle/polyelectrolyte deposition cycles were varied to generate uniformly coated nanocomposite spheres. These hybrid core-shell particles were subsequently calcined to create well- defined hollow spheres with predetermined diameters. Such hollow spheres may find application in diverse areas, ranging from photonics to fillers and pigments to microencapsulation.

[185] Nanocomposite Films Derived from Exfoliated Functional Aluminosilicate Through Electrostatic Layer-by-Layer Assembly


D. W. Kim, A. Blumstein and S. K. TripathyChem. Mater. 13(5) (2001), 1916-1922

Multilayered nanocomposite films were prepared from aluminosilicate platelets with functional chromophores and polyelectrolytes through electrostatic layer-by-layer assembly. Fluorescent dye coumarin was intercalated into the layered aluminosilicate hectorite, and the resulting hectorite/coumarin intercalation complex particles were broken down into individual platelets by means of extensive shaking and sonication of their water suspension. Atomic force microscopy (AFM) and transmission electron microscopy data show that the exfoliated platelets have the form of lathes of approximately 10-40 nm width, 150-400 nm length, and 2-3 nm average thickness. This last value is consistent with the overall thickness of a single aluminosilicate lamella sheathed with coumarin molecules on both sides. Given the strong negative surface charge of the aluminosilicate layers, films of nanocomposites could be formed by electrostatic layer-by-layer assembly using a cat;ionic polyelectrolyte. The AFM topography of such films revealed a homogeneous monolayer coverage of the underlying substrate. Linear buildup of the multilayer films of up to 20 cycles was demonstrated and investigated using UV/vis absorption spectroscopy. The resulting transparent films have exhibited strong characteristic blue-green fluorescence due to coumarin dye molecules adhered to the exfoliated hectorite platelets.

[186] Electrostatic Layer-by-Layer Assembly of Polycation and DNA Multilayer Films by Real-Time Surface-Plasmon Resonance TechniqueR. J. Pei, X. Q. Cui, X. R. Yang and E. K. WangChinese J. Chem. 19(4) (2001), 433-435

The assembly of alternating DNA and positively charged poly(dimethyldiallylammonium chloride) (PDDA) multilayer films by electrostatic layer-by-layer adsorption has been studied. Real time surface plasmon resonance (BIAcore) technique was used to characterize and monitor the formation of multilayer films in solution in real time continuously. The results indicate that the uniform multilayer can be obtained on the poly(ethylenimine) (PEI) coated substrate surface. The kinetics of the adsorption of DNA on PDDA surface was also studied by real-time BIAcore technique, and the observed rate constant was calculated using a Langmuir model (k(obs) = (1.28 +/- 0.08) x 10(-2) s(-1)).

[187] Polyelectrolyte Multilayer Capsules Templated on Biological Cells - Core Oxidation Influences Layer ChemistryS. Moya, L. Dahne, A. Voigt, S. Leporatti, E. Donath and H. MöhwaldColloid Surf. A 183(NSI) (2001), 27-40

Polyelectrolyte multilayer capsules have been fabricated in aqueous media by step-wise assembling of sodium polystyrene sulfonate (PSS) and polyallylamine hydrochloride (PAH) on human red blood cells and melamine formaldehyde resin particles as templates, followed by removal of these templates by two different procedures. The melamine formaldehyde core can be dissolved in pH 1.1. The removal of the cell cores was achieved by an oxidation with sodium hypochlorite solution (pH 12). The effect of these treatments on the chemical composition of the capsules and of a randomly formed polyelectrolyte complex was studied. The melamin resin templated capsules have basically the same composition as the untreated complex revealing no chemical changes induced by the acid. But about 20% of the total hollow capsules mass can be attributed to a rest of melamin resin. The treatment with NaOCl solution changed the chemical composition of the capsules drastically. The amino groups of polyallylamine were oxidized to nitriles, nitroso-, nitro-, azo- and carbonyl groups. Positive charges disappeared. Covalent bonds were formed which crosslink the polymer chains. Simultaneously, the amount of PSS is strongly reduced to 10% of the original value. The stability of the capsules can be understood as a result of crosslinking and hydrophobic interactions. The cell templated capsules are monodisperse, being replicas in size and shape of the template but their chemical composition is different compared with the initial polyelectrolyte multilayer film. The altered chemical properties are responsible for new physical and mechanical properties such as higher elasticity, high chemical stability, as well as selective adsorption and permeation for charged ions. (C) 2001 Elsevier Science B.V. All rights reserved.

[188] Preparation of Colloidal Gold Multilayers with 3- (Mercaptopropyl)-Trimethoxysilane as a Linker MoleculeJ. Y. Tseng, M. H. Lin and L. K. ChauColloid Surf. A 182(1-3) (2001), 239-245

A novel strategy to prepare colloidal Au multilayers using 3- (mercaptopropyl)-trimethoxysilane (MPTMS) as a linker molecule was demonstrated. The nanostructure consists of alternate layers of ultrathin thiol-functionalized silica films and Au colloids. In which, a surface sol-gel process was used to prepare the thiol-functionalized silica films. During


the self- assembly of Au colloids, a reiterative immersion-rinse approach was used to ensure maximum coverage of isolated Au colloids. The surface coverage of the first colloidal Au monolayer is ca. 45% of a dose-packed monolayer. The method yields uniform layer- by-layer growth colloidal Au multilayers through self-assembly at the Au(lll) planes, as judged by the ultraviolet-visible (UV- vis) spectroscopic data and the X-ray diffraction (XRD) patterns. (C) 2001 Elsevier Science B.V. All rights reserved.

[189] Layered Nanoarchitectures Between Cationic and Anionic Materials - Composite Assemblies of Polyions, Lipid Bilayers, and ProteinsK. Ariga, Y. Sasaki, H. Horiguchi, N. Horiuchi and J. KikuchiDEFECT DIFFUS FORUM 191 (2001), 35-59

Many functional molecules such as polyions, proteins, colloidal particles, dyes, and lipid membranes, can be assembled as thin films through layer-by-layer alternate adsorption. This technique is useful for preparing nano-sized enzyme reactors where the enzymes are sandwiched between molecular films of polyions or lipids. In order to systematically compare the enzymatic activity and the related properties between the polyion-protein assemblies and lipid-protein assemblies, in this study, we prepared both kinds of assemblies and examined their enzymatic activity. Two kinds of enzymes, lactate dehydrogenase (LDH) and alcohol dehydrogenase (ADH), were assembled with the polycation, poly(diallyldimethylammonium chloride) (PDDA), and an artificial cationic lipid. The assembling behavior was analyzed by a quartz crystal microbalance (QCM) with nanogram precision which revealed that the polyion, the lipid membrane, and the enzyme layers can be repeatedly and reproducibly assembled. The catalytic activity of the obtained films was spectrophotometrically examined. The activity of the LDH on a lipid-surface film was apparently greater than that of the LDH on a polyion-surface film. This difference might originate from the difference in the surface nature of the films. The Michaelis-Menten analysis suggested that the concentration increase in an anionic substrate in the vicinity of the cationic lipid surface led to the enhanced enzymatic activity. The surface morphology of the film was investigated using atomic force microscopy(AFM). The lipid- surface film apparently has a rough surface, while a relatively smooth surface morphology was observed for the polyion-surface film. This difference in the surface morphology might affect the activity of the immobilized enzymes.

[190] Preparation of Multilayered Nanocomposites of Polyoxometalates and Poly(Amidoamine) DendrimersL. Cheng and J. A. CoxELECTROCHEM COMMUN 3(6) (2001), 285-289

A layer-by-layer (LBL) deposition technique based on electrostatic attraction of oppositely charged species was used to fabricate multilayer films consisting of polyoxometalates (POMs) (Keggin-structure PMo12O403- or Dawson-structure P2W18O626-) and a generation-4 poly(amidoamine) dendrimer (G4- PAMAM) on quartz treated with poly(diallyldimethylammonium chloride) and gold treated with (aminothiophenol (4-ATP). Both of the UV-visible spectrophotometry and cyclic voltammetry proved a successful formation of uniform and well-defined self- assemblies with multilayered supramolecular structure. With PM0(12)O(40)(3-) each layer contained 4.6 x 10(-11) mol cm(-2). Direct attachment of PMo12O403- yielded a surface excess of 3.6 x 10(-11) mol cm(-1) in that monolayer. The comparison suggested an expansion of the effective surface area by the multicharged macromolecule, G4-PAMAM. The multilayer films mediated the reduction of iodate and of nitrite. (C) 2001 Elsevier Science B.V. All rights reserved.

[191] Shrinking of Ultrathin Polyelectrolyte Multilayer Capsules upon Annealing - A Confocal Laser-Scanning Microscopy and Scanning Force Microscopy StudyS. Leporatti, C. Gao, A. Voigt, E. Donath and H. MöhwaldEur. Phys. J. E 5(1) (2001), 13-20

Heating-induced morphological changes of micrometer size capsules prepared by step-wise deposition of oppositely charged polyelectrolytes onto melamine formaldehyde (MF) latex particles and biological cells with subsequent dissolution of the core have been investigation by confocal laser scanning microscopy (CLSM) and scanning force microscopy (SFM). For poly(styrenesulfonate-Na salt)/poly(allylamine hydrochloride) polyelectrolyte capsules a remarkable heating-induced shrinking is observed. An increase of the wall thickness corresponding to the capsule diameter decrease is found. The morphology of these microcapsules after temperature treatment is characterized. The thickening of the polyelectrolyte multilayer is interpreted in terms of a configurational entropy increase via polyanion- polycation bond rearrangement.


[192] Elasticity of Hollow Polyelectrolyte Capsules Prepared by the Layer-by-Layer TechniqueC. Gao, E. Donath, S. Moya, V. Dudnik and H. MöhwaldEur. Phys. J. E 5(1) (2001), 21-27

Osmotically induced deformations (invaginations) of polyelectrolyte capsules were observed in poly(styrene sulfonate, sodium salt) (PSS) solution since PSS of Mw 70 000 is excluded from the capsule interior. It was found that there is a critical osmotic pressure difference at which the initial spherical capsule shape becomes unstable and invaginations are formed. This critical osmotic pressure was obtained as a function of the wall thickness and the capsule size. A theoretical model is provided which describes the relationship between the critical osmotic pressure, the elasticity modulus, the capsule wall thickness, and the capsule radius. The model was verified by measuring the invagination onset as a function of particle radius and wall thickness. The elasticity modulus of the PSS/PAH (polyallylamine hydrochloride) polyelectrolyte multilayer was measured as a function of wall thickness and capsule diameter. The modulus ranges between 500 and 750 MPa, which indicates a relatively strongly interconnected polyelectrolyte multilayer structure. With higher molecular weight PAH the elasticity modulus of the PSS/PAH multilayer was slightly enhanced.

[193] Ultrathin Self-Assembled Polyelectrolyte Multilayer MembranesB. Tieke, F. Vanackern, L. Krasemann and A. ToutianoushEur. Phys. J. E 5(1) (2001), 29-39

The paper is concerned with ultrathin membranes prepared upon alternating layer-by-layer adsorption of cationic and anionic polyelectrolytes on a porous substructure. The formation of the polyelectrolyte multilayer membranes is characterised and the transport of gases, liquid mixtures and ions across the membranes is studied. In particular, the use of the membranes of alcohol/water separation under pervaporation conditions, and for the separation of mono- and divalent ions is described. It is demonstrated that upon a suitable choice of polyelectrolytes and substructures, and a careful optimisation of preparation and operation conditions, membranes can be tailored exhibiting an excellent separation capability.

[194] Complexation and Distribution of Counterions in a Grafted Polyelectrolyte LayerY. Tran and P. AuroyEur. Phys. J. E 5(1) (2001), 65-79

The complexation and the distribution of various cations, bound to a poly(styrene sulfonate) brush, have been investigated using infra-red spectroscopy and neutron reflectivity. Small counterions (like tetremethylammonium) are distributed throughout the brush in such a way that a local electroneutrality is ensured. They also exchange readily with other bulk small cations. On the other hand, model polycations are irreversibly trapped to the brush despite a relative small number of ionic bonds involved in the complexation. These complexed polycations are localized at the outer border of the brush, forming a macromolecular barrier. However, this spatial segregation does not allow the buildup of polyelectrolyte multilayers. Cationic surfactants are associated stoichiometrically with the brush sulfonates but unlike small counterions, this complexation is ''irreversible'' and induces a restructuring of the polymer interface.

[195] Xenotransplantation of Parathyroids in Rats Using Barium- Alginate and Polyacrylic-Acid Multilayer MicrocapsulesA. Gaumann, M. Laudes, B. Jacob, R. Pommersheim, C. Laue, W. Vogt and J. SchrezenmeirEXP TOXICOL PATHOL 53(1) (2001), 35-43

The integrity and function of encapsulated parathyroid tissue following xenotransplantation is limited by oxygen and nutrition supply and capsule fibrosis. Since some of these factors depend on stability and biocompatibility of the coating material, multilayer microcapsules have been developed. Parathyroid tissue pieces and digested single cells from pigs were encapsulated in barium-alginate and in polyacrylic acid (PAA) multilayer capsules. After 7 days of culture the function of the encapsulated cells were assessed. Subsequently, in a part of the cultured microcapsules the viability was directly assessed whereas the other part was transplanted in dark animal [DA] rats for 30 days. After explantation viability and fibrotic reaction were examined. Single cells showed a significant increase in parathyroid hormone [PTH] secretion when exposed to medium low in calcium, whereas minced tissue pieces revealed necrosis without stimulatory responsiveness. Morphometry showed significantly better viability of single cells compared with minced tissue in vitro and in vivo. The fibrotic reaction against capsules with minced tissue was more pronounced than for capsules containing single cells. There was no difference between barium alginate and PAA capsules when containing minced tissue. In single cells, however, the fibrous tissue reaction differed significantly between barium


alginate and PAA capsules. Encapsulated single cells of parathyroid tissue maintain detectable function and viability. In contrast minced tissue underwent necrosis and induced significantly more connective tissue reaction than single cells indicating an interrelationship between necrosis and fibrosis.

[196] Polarity of Layer-by-Layer Deposited Polyelectrolyte Films as Determined by Pyrene FluorescenceC. Tedeschi, H. Möhwald and S. KirsteinJ. Am. Chem. Soc. 123(5) (2001), 954-960

The polarity of polyelectrolyte (PE) multilayer films is investigated with pyrene as a polarity-sensitive probe. Multilayer films of poly(styrene sulfonate) (PSS) and various polycations were prepared by the layer-by-layer self-assembly technique. Pyrene (PY) molecules were inserted into the films by exposing the multilayers to pyrene solutions. By this method a homogeneous distribution of pyrene molecules at low concentration within the film was obtained. The ratio of the fluorescence intensities of the first (I) to the third (III) vibronic band (Py-value) of the pyrene emission spectrum is employed here to determine the polarity of the PE films. PSS and poly(allylamine hydrochloride) (PAH) multilayer films yielded a pyrene value close to the solvent polarity of acetone, while multilayers of PSS and poly(diallyldimethylammonium chloride) (PDADMAC) displayed a value higher than the one corresponding to water. The pyrene values of the polyelectrolyte films were independent from the solvent employed for probe dissolving. Although no direct relationship between solvent polarity and dielectric constant (epsilon) is available, an estimate of the static dielectric constant of the films can be provided by comparing the Py- values of the films with those of various solvents. Changes in the humidity conditions of the film environment in a closed cell did not affect the film polarity. However, a drastic and irreversible reduction of polarity could be induced by actively drying the samples by a nitrogen flow.

[197] 2 Modes of Linear Layer-by-Layer Growth of Nanoparticle- Polylectrolyte Multilayers and Different Interactions in the Layer-by-Layer DepositionJ. W. Ostrander, A. A. Mamedov and N. A. KotovJ. Am. Chem. Soc. 123(6) (2001), 1101-1110

The structure of the multilayer assemblies of yttrium iron garnet nanoparticles (YIG) with polyelectrolytes was investigated with the emphasis on the control of the particle density in the adsorption layers. It was found that the growth of YIG films prepared by the layer-by-layer assembly can occur via two deposition modes: (1) sequential adsorption of densely packed adsorption layers (normal growth mode) and (2) in-plane growth of isolated particle domains (lateral expansion mode). Importantly, the dependence of the optical density on the number of deposition cycles remains linear in both cases. Microscopy results indicate that the origin of the lateral growth is in the interplay of particle/particle and particle/ polyelectrolyte interactions rather than in a substrate effect. The lateral expansion mode is a general attribute of the layer- by-layer deposition and can be observed for various aqueous colloids. Fur the preparation of sophisticated multifunctional assemblies on nanoparticles, the film growth via domain expansion should be avoided, and therefore, one must be able to control the growth pattern. The switch from lateral to normal growth mode can be effected by grafting charged organic groups to YIG nanoparticles. Hydrophobic interactions between the hydrocarbon groups of the modified YIG and polyelectrolyte significantly increase the attractive component of the particle/ polyelectrolyte and particle/particle interactions. The films from modified YIG display densely packed nanoparticle layers with a greatly reduced number of defects.

[198] Weak Versus Strong - A Weak Polyacid Embedded Within a Multilayer of Strong PolyelectrolytesA. F. Xie and S. GranickJ. Am. Chem. Soc. 123(13) (2001), 3175-3176

[199] Efficient Photocurrent Generation in Novel Self-Assembled Multilayers Comprised of (60)Fullerene-Cationic Homooxacalix(X)Arene Inclusion Complex and Anionic Porphyrin PolymerA. Ikeda, T. Hatano, S. Shinkai, T. Akiyama and S. YamadaJ. Am. Chem. Soc. 123(20) (2001), 4855-4856

[200] Multiple Membranes from True Polyelectrolyte MultilayersS. T. Dubas, T. R. Farhat and J. B. Schlenoff


J. Am. Chem. Soc. 123(22) (2001), 5368-5369

[201] Fabrication of Micro Reaction Cages with Tailored PropertiesL. Dähne, S. Leporatti, E. Donath and H. MöhwaldJ. Am. Chem. Soc. 123(23) (2001), 5431-5436

Hollow polyelectrolyte capsules in micro- and submicrometer size were prepared. Their interior was functionalized by a ''ship in bottle'' synthesis of copolymers. While the monomers permeated the capsule wall easily, the formed polymers remained in the capsule cage. The physicochemical properties of the capsule interior such as ion strength, pH, light absorption, and fluorescence could be controlled independently from the surrounding solvent by means of the chemical nature of the captured polymer. In case of polyelectrolytes the osmotic pressure of the counterions led to a swelling of the capsules which can be important for micromechanics. The functionalization with light-sensitive materials allowed selective photoreactions inside the capsules. Synthesis of polyelectrolytes at high concentration resulted in an intertwining of the capsule wall with the polymer. The modified walls behaved like ion exchange membranes and showed selectivity toward adsorption and permeation of organic ions. The modified capsules offer many possibilities for novel applications as containers for controlled precipitation, as nanoreactors for catalyzed reactions, or as sensors.

[202] Photoimaging Technique on Printing Al Plate via Self-Assembly Multilayer Films Based on DiazoresinJ. Y. Chen, H. Luo, B. X. Yang and W. X. CaoJ. Appl. Polym. Sci. 80(11) (2001), 1983-1987

A photoimaging technique on a printing aluminum plate (anodized oxidation Al plate) via self-assembly multilayer thin film from nitro-containing diazoresin (NDR) as cationic polyelectrolyte and various anionic polyelectrolytes has been developed. It was confirmed that, under UV-irradiation, the linkage nature of the films changes from ionic to covalent and the solubility of the films converts dramatically, that is, the exposed area of the film becomes insoluble in H2O-DMF-LiCl (2 :4: 1 wt %) ternary solvent, but mainly the unexposed area will be dissolved. After developing in ternary solvent, an image that accepts ink easily appears on the printing Al plate. To resolve the ink-stain problem, originating from a trace remainder of the NDR on the unexposed area of the Al plate, a surface modification technique by polyphosphoric acid, which reacts with NDR to form a hydrophilic surface, was developed. The thickness, homogeneity, and surface morphology of the multilayer film ton mica) determined by atomic force microscopy and UV-vis spectra were also reported. (C) 2001 John Wiley & Sons, Inc.

[203] The Study of Layer-by-Layer Ultrathin Films by the Dynamic Contact-Angle MethodJ. Y. Chen, G. B. Luo and W. X. CaoJ. Colloid Interface Sci. 238(1) (2001), 62-69

The self-assembly film fabricated via the layer-by-layer technique was studied by the dynamic contact angle (DCA) method (wilhelmy plate method). The used polyelectrolytes are poly(diallyl-dimethylammonium chloride) (PDDA), poly(etheleneimine) (PEI), diphenylamine-4-diazonium- formaldehyde resin (DR), 2-nitro-N-methyl-4-diazonium- formaldehyde resin (NDR), and poly(sodium-p-styrenesulfonate) (PSS). For the self-assembly systems of PDDA/ PSS, PEI/PSS, DR/ PSS, and NDR/PSS, their individual contact angle fluctuates regularly with the fabrication of each layer, while the magnitude of different systems' contact angle depends on the participant polycation. The re-organization of components and the adjacent layer interpenetration are presented here to explain this phenomena. We also found that DR or NDR can adsorb itself via the layer-by-layer method to form multilayer him, and the hydrophobic interaction is put forward to effect this process. Moreover, the procedure of washing and drying after adsorption was studied and considered as a prerequisite for the successful fabrication, especially of the same charge carried components. (C) 2001 Academic Press.

[204] Preparation of Luminescent Polyelectrolyte/Cu-Doped ZnSe Nanoparticle Multilayer Composite FilmsE. C. Hao, H. Zhang, B. Yang, H. Ren and J. C. ShenJ. Colloid Interface Sci. 238(2) (2001), 285-290

ZnSe and Cu-doped ZnSe nanoparticle aqueous suspensions were prepared in the presence of mercaptopropionic acid (MPA). Cu- doped ZnSe nanoparticles exhibited a strong blue emission that was strongly dependent upon the Cu


dopant level and the chemical surface passivation produced by zinc-mercaptopropionic acid complexes. These Cu-doped ZnSe nanoparticles were further assembled into ultrathin polymer-supported films using electrostatic interactions and the layer-by-layer assembly method. UV-visible spectroscopy and X-ray photoelectron spectroscopy (XPS) provided evidence for the presence and optical activity of Cu-doped ZnSe nanoparticles within the polymer ultrathin films. Moreover, XPS data supported the presence of zinc mercaptopropionic acid complexes on nanoparticle surfaces and the presence of Cu+ ions with high luminescent activity in the doped nanoparticles. (C) 2001 Academic Press.

[205] Layer-by-Layer Construction of Novel Biofunctional Fluorescent Microparticles for Immunoassay ApplicationsW. J. Yang, D. Trau, R. Renneberg, N. T. Yu and F. CarusoJ. Colloid Interface Sci. 234(2) (2001), 356-362

A novel class of biofunctional fluorescent microparticles for application in immunoassays was constructed by using the layer- by-layer self-assembly method to deposit multiple layers of fluorescently labeled polyelectrolytes onto colloidal particles, followed by deposition of a protein (immunoglobulin G, IgG) layer. Microelectrophoresis experiments revealed alternating negative and positive zeta -potentials with deposition of each successive polyelectrolyte layer, indicating that the alternate electrostatic adsorption of polyelectrolytes of opposite charge was successfully achieved. Transmission electron microscopy images showed a change of the particle surface texture after polyelectrolyte multilayer deposition. Fluorescence microscopy image (FMI) analysis provided direct measurement of the fluorescence intensity of single microparticles. The observed systematic increase of the fluorescence intensity of individual microparticles with increasing polyelectrolyte layer number from FMI analysis further demonstrated the controlled regular adsorption of polyelectrolyte layers onto the polystyrene (PS) particles. Protein immobilization onto the polyelectrolyte multilayer- coated particles was verified by the different surface properties of the microparticles with respect to surface charge under pH conditions above and below the isoelectric point of the proteins. The assembly of IgG and fluorescein isothiocyanate-labeled IgG onto polyelectrolyte multilayer- coated PS microparticles and their potential use was ultimately confirmed by a solid phase immunotest. (C) 2001 Academic Press.

[206] Formation and Characterization of Heteropolyacid/Polycation Multilayer Films on Gold ElectrodeZ. L. Cheng, L. Cheng, S. J. Dong and X. R. YangJ. Electrochem. Soc. 148(5) (2001), E227-E232

Ultrathin multilayer films of a polybasic lanthanide heteropoly tungstate-molybdate complex and a cationic polymer of quaternized poly(4-vinylpyridine) partially complexed with osmium bis(2,2'-bipyridine) have been fabricated on a gold electrode precoated with a cysteamine self-assembled monolayer. The multilayer films have been characterized by optical spectroscopy, small-angle X-ray diffraction, and electrochemical methods (cyclic voltammetry and electrochemical impedance). Especially, the electrochemical impedance spectroscopy is developed to monitor the layer deposition processes. It provides important information such as double- layer capacitance and charge-transfer resistance. All obtained results reveal regular film growth with each layer adsorption. (C) 2001 The Electrochemical Society.

[207] Novel Polyelectrolyte Multilayer Microcapsule and Nanocapsule as Magnetic CarriersA. Voigt, N. Buske, G. B. Sukhorukov, A. A. Antipov, S. Leporatti, H. Lichtenfeld, H. Baumler, E. Donath and H. MöhwaldJ MAGN MAGN MATER 225(1-2) (2001), 59-66

Polyelectrolyte multilayer (PEM) capsules are introduced as versatile magnetic carrier systems. Superparamagnetic magnetite is mounted to the multilayer shell itself or is a component of the capsule interior. The PEM is formed at different (decomposable) colloidal templates, e.g. melamine formaldehyde resin, glutaraldehyde fixed red blood cells, emulsion oil droplets. The results are illustrated by transmission electron microscopy and confocal laser scanning microscopy. (C) 2001 Elsevier Science B.V. All rights reserved.

[208] Self-Assembly Films from Diazoresin and Carboxy-Containing PolyelectrolytesH. Luo, J. Y. Chen, G. B. Luo, Y. N. Chen and W. X. CaoJ. Mater. Chem. 11(2) (2001), 419-422


Multilayer films from diazoresin (I) and poly(sodium acrylate) (II) or a hydrolyzed maleic anhydride-styrene copolymer (III) have been fabricated on mica. During the fabrication process the absorbance of the film at 380 epsilon nm, which is the characteristic absorption of the diphenylamine 4-diazonium group of I, increases about 0.033 for each fabrication cycle. This means that the thickness of the film increases regularly. Under irradiation with UV light or heating, following the decomposition of the diazonium group, the ionic bond in the film structure converts to a covalent bond; this conversion was preliminarily verified by FTIR spectrum analysis. The stability of the different films (irradiated or unirradiated) was determined by UV-vis spectroscopy and the results show that the resistance of the film to etching by polar solvents increases significantly after bond conversion.

[209] Precipitation of Multilayered Core-Shell TiO2 Composite Nanoparticles Onto Polymer LayersM. T. Wang and L. D. ZhangJ. Mater. Res. 16(3) (2001), 765-773

A composite film of titanium dioxide (TiO2) nanoparticles and hydrolyzed styrene-maleic anhydride alternating copolymer (HSMA) was obtained on a substrate when a TiCl4 solution was heated at 80 degreesC with a spin-cast thin HSMA film present in the solution. The composite film was characterized with x- ray photoelectron spectroscopy and transmission electron microscopy. Results revealed that TiO2 nanoparticles discretely dispersed on the poly-mer layer, and they were dominantly rutile phase, of a spherical shape and 18-20 nm in diameter. In contrast, mainly amorphous TiO2 powders were obtained from the identical TiCl4 solution by drying the solution with the absence of the HSMA film. The TiO2 nanoparticles deposited on the polymer layer were regarded to contain polymer chains, rind a multilayered core-shell model was suggested for the formation of these composite nanoparticles. It is regarded that the core of a composite particle consisted of an anatase-phase TiO2 colloidal nanoparticle, while the shell layer was made of rutile-phase TiO2/polymer multilayers; the composite particles formed by a layer-by-layer self-assembly of TiO2 and polymer layers analogous to biomineralization, where the polymer promoted the crystallization of rutile-phase TiO2 when TiO2 deposited from solution.

[210] Fabrication of Polyaniline/Phthalocyanine Hybrid Ultrathin Films via Electrostatic Attraction and Doping ReactionD. Li, Y. D. Jiang, Y. R. Li, X. J. Yang, L. D. Lu and X. WangJ. Mater. Sci. Lett. 20(3) (2001), 233-235

[211] Self-Assembled Polyelectrolyte Multilayer Membranes with Highly Improved Pervaporation Separation of Ethanol/Water MixturesL. Krasemann, A. Toutianoush and B. TiekeJ. Membrane Sci. 181(2) (2001), 221-228

Ethanol/water pervaporation through ultrathin polyelectrolyte multilayer membranes is described. The membranes were prepared by the layer-by-layer technique, i.e. by alternating sequential adsorption of cationic and anionic polyelectrolytes on a porous support. The separation capability was optimized by variation of the chemical structure of the polyelectrolytes, by variation of pH and ionic strength of the polyelectrolyte solutions used for membrane preparation and by annealing of the polyelectrolyte membranes. It was found that the separation is mainly affected by the charge density of the polyelectrolytes which is controlled by the chemical structure and the degree of ionisation of the polar groups. Selectivity for water was highest, if polyelectrolytes of high charge density such as polyethyleneimine (PEI), polyvinylamine (PVA) and polyvinylsulfate (PVS) were used and if the pH of the polyelectrolyte solutions was equal to the mean of the pK(a) values of the corresponding cationic and anionic polyelectrolyte. Best results were obtained for PVA/PVS and PEI/ PVS membranes which are characterized in detail with regard to their separation behavior. (C) 2001 Elsevier Science B.V. All rights reserved.

[212] Pervaporation Separation of Water/Alcohol Mixtures Using Composite Membranes Based on Polyelectrolyte Multilayer AssembliesJ. Meierhaack, W. Lenk, D. Lehmann and K. LunkwitzJ. Membrane Sci. 184(2) (2001), 233-243

Composite pervaporation membranes composed of an asymmetric polyamide-6 membrane and an ultrathin self-assembled polyelectrolyte separating layer are described. The supporting membrane was prepared from both an unmodified polyamide-6 and a comb-like polymer with carboxyl terminated polyamide-6 side chains. A high end group concentration was found to be advantageous for sufficient adhesion of the multilayer systems on the supports.


Up to 20 layers were deposited onto the membrane surface by dipping the membranes in aqueous solutions containing oppositely charged polyelectrolytes. The polyanions used were poly(acrylic acid), poly(styrene sulfonic acid) and alginic acid. The polycations used were poly(diallyldimethylammoniumchloride), chitosan and poly(ethylenimine). Performance of these membranes depends strongly on the layer number and on the type of polyelectrolytes. In general, membranes modified with two weak polyelectrolytes of high charge density gave the best separation properties while those modified with strong polyelectrolytes of low charge density led to poorer separation properties. However, the highest separation factor (greater than or equal to 10,000) for a water/2-propanol mixture (12/88 w/w) at permeate flux of 300 g/m(2)h was obtained with six double layers consisting of poly(ethylenimine) and alginic acid. These composite membranes were stable over an operating period of at least 400 h. (C) 2001 Elsevier Science B.V. All rights reserved.

[213] Biological Cells as Templates for Hollow MicrocapsulesB. Neu, A. Voigt, R. Mitlohner, S. Leporatti, C. Y. Gao, E. Donath, H. Kiesewetter, H. Möhwald, H. J. Meiselman and H. BaumlerJ. Microencapsul. 18(3) (2001), 385-395

Microcapsules in the micrometer size range with walls of nanometer thickness are of both scientific and technological interest, since they can be employed as micro- and nano- containers. Liposomes represent one example, yet their general use is hampered due to limited stability and a low permeability for polar molecules. Microcapsules formed from polyelectrolytes offer some improvement, since they are permeable to small polar molecules and resistant to chemical and physical influences. Both types of closed films are, however, limited by their spherical shape which precludes producing capsules with anisotropic properties. Biological cells possess a wide variety of shapes and sizes, and, thus, using them as templates would allow the production of capsules with a wide range of morphologies. In the present study, human red blood cells (RBC) as well as Escherichia coli bacteria were used; these cells were fixed by glutardialdehyde prior to layer-by-layer (LbL) adsorption of polyelectrolytes. The growth of the layers was verified by electrophoresis and flow cytometry, with morphology investigated by atomic force and electron microscopy; the dissolution process of the biological template was followed by confocal laser scanning microscopy. The resulting microcapsules are exact copies of the biological template, exhibit elastic properties, and have permeabilities which can be controlled by experimental parameters; this method for microcapsule fabrication, thus, offers an important new approach for this area of biotechnology.

[214] Sustained-Release Properties of Polyelectrolyte Multilayer CapsulesA. A. Antipov, G. B. Sukhorukov, E. Donath and H. MöhwaldJ. Phys. Chem. B 105(12) (2001), 2281-2284

Layer-by-layer (LbL) assembly of oppositely charged polyelectrolytes was used to coat fluorescein particles. These particles, with a size of 4-9 mum, were prepared by precipitation of fluorescein at pH 2. Polystyrensulfonate (PSS) and polyallylamine (PAH) were used to form a polyelectrolyte shell on the fluorescein core. The permeation of fluorescein molecules through the polyelectrolyte shell during core dissolution was monitored at pH 8 by the increasing fluorescence intensity as a result of dequenching. The number of polyelectrolyte layers sufficient to sustain fluorescein release was found to be 8-10. Increasing the number of layers prolonged the core dissolution time for minutes. The permeability of polyelectrolyte multilayers of the thickness of 20 nm for fluorescein is about 10(-9) m/s. The features of the release profile and possible applications of the LbL method for shell formation in order to control release properties for entrapped materials are outlined.

[215] Optical-Properties of Thin-Films of Au-at-SiO2 ParticlesT. Ung, L. M. Lizmarzan and P. MulvaneyJ. Phys. Chem. B 105(17) (2001), 3441-3452

Homogeneous films of Au@SiO2 particles have been deposited on glass as a prototype 3D ''artificial solid'' using the LBL method. The film thickness is controlled by the number of dipping cycles and is measured by AFM. Each cycle results in approximately one monolayer of particles being deposited. The particle films are dense, but disordered. The optical properties of the resulting thin films have been analyzed as a function of the particle volume fraction, which is controlled through the silica shell thickness. We find that the surface plasmon peak position in films with volume fractions up to phi > 0.5 is accurately predicted by the Maxwell-Garnett model. The films exhibit remarkably uniform, transmitted colors and display metallic reflection at low angles of incidence, even at low volume fractions. The films can be annealed at T > 500 K to provide extremely stable, optical films.


[216] Metal-Ion Sensing Using Ultrathin Organic Films Prepared by the Layer-by-Layer Adsorption TechniqueC. Pearson, J. Nagel and M. C. PettyJ. Phys. D, Appl. Phys. 34(3) (2001), 285-291

Bilayer films of poly(ethyleneimine) and poly(ethylene-co- maleic acid) have been prepared using the layer-by-layer assembly technique. These films have been characterized using surface plasmon resonance (SPR). Exposure to aqueous solutions of metal acetate (metal = copper, nickel) resulted in a shift in the position of the SPR curve. This shift could be monitored by observing the intensity of the reflected laser beam at fixed angle and concentrations of copper acetate down to at least 10(- 6) M could be detected.

[217] Protein Adsorption Onto Auto-Assembled Polyelectrolyte FilmsG. Ladam, P. Schaaf, F. J. G. Cuisinier, G. Decher and J. C. VoegelLangmuir 17(3) (2001), 878-882

We investigate the adsorption processes of a series of positively and negatively charged proteins onto the surface of polyelectrolyte multilayers. We find that proteins strongly interact with the polyelectrolyte film whatever the sign of the charge of both the multilayer and the protein. When the charges of the multilayer and the protein are similar, one usually observes the formation of protein monolayers which can become dense. We also show that when the protein and the multilayer become oppositely charged, the adsorbed amounts are usually larger and the formation of thick protein layers extending up to several times the largest dimension of the protein can be observed. Finally, we find that proteins are mainly adsorbed in a strong way on polyelectrolyte multilayers and protein surface diffusion is strongly suggested. Our results confirm that electrostatic interactions play an important role in polyelectrolyte multilayer/protein interactions.

[218] Controlling the Permeability of Multilayered Polyelectrolyte Films Through Derivatization, Cross-Linking, and HydrolysisJ. H. Dai, A. W. Jensen, D. K. Mohanty, J. Erndt and M. L. BrueningLangmuir 17(3) (2001), 931-937

Partial Fischer esterification of poly(acrylic acid) allows tailoring of the hydrophobicity and charge density of multilayered films containing poly(allylamine hydrochloride) (PAH) and derivatized poly(acrylic acid) (d-PAA). As hydrophobicity and charge density strongly affect film permeability, control over these properties is vital for possible applications of PAH/d-PAA films as ion-separation membranes and sensors. The hydrophobicity of these films depends on both the extent of esterification and the nature of the derivatizing alcohol. Even though PAH/d-PAA films are composed of polyelectrolytes, the presence of hydrophobic ester groups results in advancing water contact angles as high as 101 degrees. The hydrophobicity of these coatings allows them to effectively passivate underlying electrodes as shown by minimal peak currents in cyclic voltammograms (CVs) of RU(NH3)(6)(3+) and Fe(CN)(6)(3-). Cross-linking of hydrophobic PAH/ d-PAA films via heat-induced amidation stabilizes coatings over a wide pH range but does not significantly decrease the already low film permeability to Ru(NH3)(6)(3+) and Fe(CN)(6)(3-). Stabilization due to cross-linking does, however, allow base- promoted hydrolysis of the ester groups of PAH/d-PAA coatings. After hydrolysis, films are extremely hydrophilic and selectively permeable to Ru(NH3)(6)(3+) over Fe(CN)(6)(3-) due to,the high density of newly formed -COO- groups. In the case of some hydrolyzed films, the presence of small concentrations of Ca2+ results in dramatic current decreases in CVs of RU(NH3)(6)(3+), suggesting possible use of these films in sensing applications.

[219] Molecular-Weight Dependence of Alternate Adsorption Through Charge-Transfer InteractionY. Shimazaki, R. Nakamura, S. Ito and M. YamamotoLangmuir 17(3) (2001), 953-956

[220] Layered Polyelectrolyte Films on Au Electrodes - Characterization of Electron-Transfer Features at the Charged Polymer Interface and Application for Selective Redox ReactionsV. Pardoyissar, E. Katz, O. Lioubashevski and I. WillnerLangmuir 17(4) (2001), 1110-1118


Oppositely charged polyelectrolyte assemblies of poly(acrylic acid) and poly-L-lysine are deposited as alternate layers on cystamine-functionalized Au surfaces. Microgravimetric, quartz- crystal-microbalance, measurements and ellipsometric studies reveal a nonlinear increase in the polymer assembly thickness upon the buildup of the polymer layers. This is attributed to the swelling of the polymer upon the stepwise assembly of the layered film. The interfacial and intra-assembly properties of the polyelectrolyte systems were characterized by Faradaic impedance spectroscopy. In the presence of Fe(CN)(6)(3-)/ Fe(CN)(6)(4-) as the redox label, all assemblies that terminate with a negatively charged interface are characterized by a high interfacial electron-transfer resistance, originating from the electrostatic repulsion of the redox label from the interface. The interfacial electron-transfer resistance also increases as the number of layers, or assembly thickness, increases. For assemblies terminated with a positively charged polyelectrolyte, a very low interfacial electron-transfer resistance for the redox process of the negatively charged redox probe is detected. This is attributed to a neutralized, porous structure of the polymer assembly. For the positively charged redox label, protonated N,N-dimethylaminomethyl- ferrocene, similar results are observed for the assemblies with the opposite dependence on the charge of the terminal layer. The electrodes functionalized with the polymers were used for the selective oxidation of a mixture consisting of Fe(CN)(6)(4- ) and protonated N,N-dimethylaminomethyl-ferrocene.

[221] Ion-Transport and Equilibria in Polyelectrolyte MultilayersT. R. Farhat and J. B. SchlenoffLangmuir 17(4) (2001), 1184-1192

Transport of redox-active probe ions through multilayers made from highly charged polyelectrolytes is described. Because of intrinsic charge balance between polyelectrolyte segment ion pairs, there are no sites for the exchange of small ions within the bulk of as-made multilayers. In the presence of salt in the external bathing solution, sites for small ion exchange are forced into these ''reluctant'' amphoteric exchangers. Equilibrium considerations lead to the conclusion that, under conditions of high salt concentration and strong polymer ion pairing, the exchanger site concentration is proportional to the solution salt concentration, while the population of redox ions within the multilayer remains constant. Rotating disk electrodes coated with multilayers yield cyclic voltammograms which retain their classical sigmoidal shape, indicating well- behaved membrane transport. Limiting currents are strongly attenuated by membranes of thickness on the order of a few hundred angstroms. Layer-by-layer buildup reveals enhanced transport of negative ions through multilayers bearing a positive surface charge, attributed to Donnan-enhanced membrane inclusion of negative ions. Good matching of internal charge, efficiently excluding ions, is a distinctic feature of membranes made from polyelectrolyte multilayers. The flux through membranes is a strongly nonlinear function of salt concentration for the multiply charged ferro- and ferricyanide ions. This leads to significant transport selectivity between ions, favoring species with lower charge. With the membrane concentration of redox ion, charge n, constant, membrane flux is proportional to membrane diffusion coefficient, (D) over bar, which depends on solution salt concentration in the manner (D) over bar similar to k [salt](n). The implications of this for membrane transport control of multiply charged biomolecules are discussed.

[222] Fuzzy Assembly and 2nd-Harmonic Generation of Clay/Polymer/Dye Monolayer FilmsB. Vanduffel, T. Verbiest, S. Vanelshocht, A. Persoons, F. C. Deschryver and R. A. SchoonheydtLangmuir 17(4) (2001), 1243-1249

Fuzzy assembled multicompound films consisting of natural and synthetic colloidal clay particles, poly(diallyldimethylammonium chloride) (PDDA) and the dyes methylene blue (MB+) and 4-(4-[N-allyl-N-methylamino] phenylazo)benzenesulfonic acid, sodium salt (NAMO(-)) have been prepared. The organization of the clay particles was imaged by means of atomic force microscopy. Fuzzy assembled glass/clay/ methylene blue films have been investigated by visible spectroscopy, and the spectra were explained in terms of the substrate-clay interaction and clay particle overlap. Glass/ clay/PDDA/NAMO films were investigated by means of absorption spectroscopy, polarized absorption spectroscopy, and second harmonic generation. The nonlinear optical properties of the films were found to be determined by the adsorbed amount of NAMO and its noncentrosymmetric organization. These factors are in turn governed by the substrate type, the PDDA concentration, and the clay type. Optimized second harmonic generation for the glass/laponite/ PDDA/NAMO films was found in which the clay particles are deposited-onto a (3-aminopropyl)-trimethoxysilane modified glass surface and PDDA chains are adsorbed from a 0.1 M solution.

[223] Release Behavior of Thin-Walled Microcapsules Composed of Polyelectrolyte MultilayersX. Y. Shi and F. CarusoLangmuir 17(6) (2001), 2036-2042


The release properties of the fluorescent probe pyrene, PYR, encapsulated in polyelectrolyte multilayer capsules were examined by fluorescence spectroscopy. PYR was encapsulated by the layer-by-layer deposition of oppositely charged polyelectrolytes onto PYR microcrystal templates, and its release was accomplished by exposing the polyelectrolyte-coated microcrystals to ethanol solutions. Solubilization of the hydrophobic probe by ethanol resulted in its expulsion from the core through th permeable polyelectrolyte: multilayer shells. The PYR release rate, quantified by following the monomer fluorescence of the solubilized PYR as a function of time, decreased with increasing number of polyelectrolyte layers deposited onto the microcrystal cores. In addition, two amphiphiles (sodium dodecyl sulfate and dipalmitoyl-(DL)-alpha - phosphatidylcholine) used to disperse the microcrystals in aqueous solution prior to coating with polyelectrolytes significantly influenced the PYR release rate. The maximum release time, defined as the time required to achieve saturation release, could be varied by a factor of 2-5 depending on the nature of the first adsorbed layer and the number of polyelectrolyte layers composing the shell wall. The influence of flow (i.e., centrifugation vs magnetic stirring) as well as solvent on the PYR release rate is also discussed.

[224] Formation of Multilayer Composite-Particles Comprised of Silica/ Vesicle/Silica Particles by HeterocoagulationB. Yang, H. Matsumura, K. Katoh, H. Kise and K. FurusawaLangmuir 17(8) (2001), 2283-2286

The multilayer composite particles comprised of silica/PC (phosphatidylcholine) vesicle/silica particles have been prepared by using the heterocoagulation technique. The formation process is as follows: at first, large silica particles (2r = 1.5 mum) and PC vesicles (2r = 0.2 mum) were mixed at a definite particle number ratio in 10(-4) M LaCl3 aqueous solution. The PC vesicle/silica composites were spontaneously formed by mutual electrostatic attraction. After removal of the excess PC vesicles from the system, the small silica particle (2r = 0.5 mum) suspension was added into the PC vesicle/silica composite dispersions to form the multilayer composite particles composed of small silica, PC vesicle, and core silica particles. The formation of multilayer composite particles was confirmed by the electrophoresis, dynamic light scattering (DLS), and adsorption measurements of PC molecules. Finally, the existence of multilayers was confirmed directly using a special optical microscope.

[225] Influence of Thickness on Catalytic Efficiency of Cobalt Corrin- Polyion Scaffolds on Electrodes in MicroemulsionsC. J. Campbell, C. K. Njue, B. Nuthakki and J. F. RuslingLangmuir 17(11) (2001), 3447-3453

Catalytic electrodes were prepared by covalently binding poly-L- lysine (PLL) onto oxidized carbon electrodes and then linking the cobalt corrin vitamin B-12 hexacarboxylic acid [B- 12(COOH)(6)] to this surface. Additional layers of PLL-B- 12(COOH)(6) were attached in a similar way. Quartz crystal microbalance studies showed regular and reproducible layer formation. Electrochemical and catalytic properties of the (CoL)-L-II/ (CoL)-L-I redox couple in these films were investigated using voltammetry and preparative electrolysis in an sodium dodecyl sulfate microemulsion. These films obeyed theoretical predictions of a maximum in voltammetric catalytic efficiency as thickness increased for the reduction of 1,2- dibromocyclohexane (DBCH) in a microemulsion. In films with less' than optimum thickness, kinetic control of the chemical reaction between (CoL)-L-I and DBCH predominated. As film thickness was increased beyond that found for maximum efficiency, electron and reactant mass transport within the films became limiting factors. Under synthetic electrolysis conditions, optimal turnover numbers were found for very thin films on porous electrodes, and best yields and current efficiencies were obtained with the relatively small catalyst coverage of about 2 nmol cm(-2).

[226] Stability and Mechanical-Properties of Polyelectrolyte Capsules Obtained by Stepwise Assembly of Poly(Styrenesulfonate Sodium- Salt) and Poly(Diallyldimethyl Ammonium) Chloride Onto Melamine Resin ParticlesC. Y. Gao, S. Leporatti, S. Moya, E. Donath and H. MöhwaldLangmuir 17(11) (2001), 3491-3495

Capsules composed of poly(styrene sulfonate, sodium salt) (PSS)/ poly(diallyldimethyl ammonium) chloride (PDADMAC) were prepared by layer-by-layer deposition of the polyelectrolytes on melamine formaldehyde colloidal templates followed by the decomposition of the cores by hydrochloride. A yield of more than 90% of intact capsules was achieved if (i) the core diameter was equal to or less than 3.8 mum and (ii) not more than five pairs of layers were adsorbed. When the cores were larger or the layers were thieber, the osmotic pressure difference caused by core dissolution led to an increased frequency of wall rupture. The elasticity modulus of a multilayer consisting of five pairs of PSS/PDADMAC was about 140 MPa as measured by osmotic pressure induced capsule deformation.


[227] Ex-Situ SFM Study of 2-D Aggregate Geometry of Azobenzene Containing Bolaform Amphiphiles After Adsorption,at the Mica/ Aqueous Solution InterfaceB. Zou, L. Y. Wang, T. Wu, X. Y. Zhao, L. X. Wu, X. Zhang, S. Gao, M. Gleiche, L. F. Chi and H. FuchsLangmuir 17(12) (2001), 3682-3688

Self-assembled nanometer-sized stripes are obtained spontaneously by electrostatic adsorption of bolaform amphiphiles bearing hydrophilic :pyridinium headgroups and rigid hydrophobic azobenzene onto mica sheets. The ordered stripes have a repeat spacing of 10 nm, and the ordered region can extend over: macroscopic areas. The formation of such nanostructures mainly depends on the concentration of the bolaform amphiphiles. The template effect of the mica sheet also plays a crucial role in the molecular organization at the Liquid solid interface. The degree of order of the stripes is influenced by adding electrolyte into the aqueous solution or upon irradiating the solution for physical adsorption under UV light.

[228] Ionic Self-Assembly of Glucose-Oxidase with Polycation Bearing Os ComplexJ. Q. Sun, Y. P. Sun, Z. Q. Wang, C. Q. Sun, Y. Wang, X. Zhang and J. C. ShenMACROMOL CHEM PHYSICS 202(1) (2001), 111-116

Multilayer assemblies of glucose oxidase (GOD) and poly(4- vinylpyridine) complex of osmium were fabricated on a quartz slide or a gold electrode by ionic self-assembly technique. Cyclic voltammogram experiments showed that osmium transferred electrons successfully between the immobilized GOD and the electrode surface. Its application as a glucose sensor was greatly anticipated.

[229] Investigation of the Covalently Attached Multilayer Architecture Based on Diazo-Resins and Poly(4-Styrene Sulfonate)J. Q. Sun, Z. Q. Wang, L. X. Wu, X. Zhang, J. C. Shen, S. Gao, L. F. Chi and H. FuchsMACROMOL CHEM PHYSICS 202(7) (2001), 967-973

[230] Organometallic Polyelectrolytes - Synthesis, Characterization and Layer-by-Layer Deposition of Cationic Poly(Ferrocenyl(3- Ammoniumpropyl)Methylsilane)M. A. Hempenius, N. S. Robins, R. G. H. Lammertink and G. J. VancsoMACROMOL RAPID COMMUN 22(1) (2001), 30-33

Communication: The water soluble poly(ferrocenylsilane) polycation, poly(ferrocenyl(3-ammoniumpropyl)methylsilane), was synthesized by transition metal-catalyzed ring-opening polymerization of the novel [1]ferrocenophane Fe(eta - C5H4)(2)SiCH3(CH2)(3)Cl and by subsequent side group modification. Amination of the chloropropyl moieties using potassium 1,1,3,3-tetramethyldisilazide followed by acidic hydrolysis produced the polycation. The polycation was employed together with poly(sodium vinylsulfonate) in the electrostatic layer-by-layer self-assembly process to form organometallic multilayers on quartz. The multilayer fabrication process was monitored using UV/Vis absorption spectroscopy and XPS.

[231] PH-Controlled Macromolecule Encapsulation in and Release from Polyelectrolyte Multilayer NanocapsulesG. B. Sukhorukov, A. A. Antipov, A. Voigt, E. Donath and H. MöhwaldMACROMOL RAPID COMMUN 22(1) (2001), 44-46

Communication: pH-Controlled encapsulation in and release of macromolecules from polyelectrolyte capsules of a few microns in diameter is demonstrated. Capsules were prepared via alternating adsorption of the oppositely charged polymers poly(allylamine hydrochloride) and poly(styrene sulfonate) onto decomposable melamin formaldehyde cores. The capsules were open for macromolecules at pH values below 6 and closed at pH > 8. Permeation and encapsulation of FITC-dextran (MW 75 000) into polyelectrolyte multilayer capsules. Top: pH 10, center: pH 3, bottom: pH increased to 10 after the capsules were loaded with FITC-dextran at pH 3. The bulk FITC-dextran was removed by washings at pH 10.


[232] Fabrication of a Stable Layer-by-Layer Thin-Film Based on Diazoresin and Phenolic Hydroxy-Containing Polymers via H- BondingT. B. Cao, J. Y. Chen, C. H. Yang and W. X. CaoMACROMOL RAPID COMMUN 22(3) (2001), 181-184

Using the self assembly technique, a stable multilayer films was successfully fabricated from diazoresin (DR) and poly(styrene-co-(N-(p-hydroxyphenyl)maleimide)) (P(S-co-HPMI)) followed by UV irradiation. The driving force of the self- assembly was confirmed to be H-bonding attraction between the diazonium group (-N-2(+)) Of DR and the phenolic hydroxy group (-Ph-OH) of P(S-co-HPMI). A linkage conversion from H-bond to covalent bond takes place after decomposition of the -N-2(+) group using UV irradiation. As a result, the stability of the film towards polar solvents increases dramatically.

[233] Fabrication of a Covalently Attached Multilayer Film via in- Situ ReactionJ. Y. Chen, G. B. Luo and W. X. CaoMACROMOL RAPID COMMUN 22(5) (2001), 311-314

A covalently linked ultrathin multilayer film was fabricated from 2-nitro-N-methyl-diphenyl-amine-4-diazonium-formaldehyde resin (PR) in methanol in-situ. The UV-vis, XRD, AFM and FTIR show that his multilayer is of high regularity, smoothness and stability.

[234] Selective Interaction Between Proteins and the Outermost Surface of Polyelectrolyte Multilayers - Influence of the Polyanion Type, pH and SaltM. Muller, T. Rieser, P. L. Dubin and K. LunkwitzMACROMOL RAPID COMMUN 22(6) (2001), 390-395

Protein adsorption was studied by insitu ATR-FT-IR spectroscopy of consecutively deposited polyelectrolyte multilayer systems terminated either with poly(ethyleneimine) (PEI) or polyanions, such as poly(acrylic acid) (PAC), poly(maleic acid-co- propylene) (PMA-P) or poly(vinyl sulfate) (PVS). The influence of the polyanion type, pH and ionic strength was investigated. Negatively charged human serum albumin (HSA) was strongly repelled by multilayers terminated with weak polyanions (PAC, PMA-P), whereas moderate attraction was observed for those terminated with the strong polyanion PVS. Changing the pH from 7.4 to 5 resulted in enhanced HSA adsorption onto PAC- terminated multilayers. An increase in ionic strength diminished the attractive HSA adsorption onto PEI-terminated multilayers. For the PEI/PAC system, the biomedically relevant adsorption of human fibrinogen (FGN) is determined via its isoelectric point in accordance with three other proteins.

[235] Mechanism of Polyelectrolyte Multilayer Growth - Charge Overcompensation and DistributionJ. B. Schlenoff and S. T. DubasMacromolecules 34(3) (2001), 592-598

A mechanism for distributing excess polymer surface charge is used to model the growth of multilayers of strongly charged polyelectrolytes. Two parameters are required for the semiempirical analysis: the surface, or unrestricted, charge overcompensation level, phi, which is assumed to decrease exponentially from the film surface to bulk, and the characteristic length for this decay, l(cp), which is termed the charge penetration length. Modeling of the data reveals that only modest levels of polymer charge overcompensation are required to account for large increments in polymer thickness, realized at high salt concentration, since the excess charge is distributed over several ''layers''. Experimentally, phi appears to be roughly independent of salt concentration. The thickness increment is primarily controlled by l(cp), which is about 2.5 nominal layers for the system studied. Whereas the growth conditions and polyelectrolyte type lead to the formation of intrinsically compensated multilayers in this work, conditions for obtaining extrinsic compensation are also discussed. Kinetic vs thermodynamic limitations for polymer addition during a deposition cycle are contrasted.

[236] Stepwise Assembly of Enantiomeric Poly(Lactide)S on SurfacesT. Serizawa, H. Yamashita, T. Fujiwara, Y. Kimura and M. Akashi


Macromolecules 34(6) (2001), 1996-2001

Enantiomeric poly(lactide)s were assembled on a quartz crystal microbalance (QCM) substrate, which detects the mass of the polymers from the frequency shift, following immersion of QCM into alternating acetonitrile solutions. A quantitative QCM analysis at each step and a differential scanning calorimetric study of the assembly showed racemic crystal (stereocomplex) formation on the substrate surface. Atomic force microscopic observation showed a dotted nanostructure of the assembly. The assembly amount was increased with increasing the PLA concentration and the immersion time, while that was decreased with increasing the assembly temperature. The heterogeneous assembly was also prepared by altering the immersion time. We found that racemic crystal formation was applied to the alternate deposition of certain structurally regulated polymers.

[237] Coating of Colloidal Particles by Controlled Precipitation of PolymersV. Dudnik, G. B. Sukhorukov, I. L. Radtchenko and H. MöhwaldMacromolecules 34(7) (2001), 2329-2334

A method is suggested for the coating of micron-sized particles by polymeric films based on surface-controlled precipitation. Polymer particles were coated by dextran and DNA in a water/ ethanol mixture containing multivalent cations. A theoretical model for depositing polymers on colloidal particles is presented using the Smoluchowski solution for diffusion- controlled irreversible coagulation. Theoretical estimations appear to provide the proper particle and polymer concentration ranges in order to achieve smooth coverage. The optimal concentration range also was determined experimentally and agrees with the theoretical calculations. The controlled precipitation method of assembling thin films on colloids is compared with the layer-by-layer adsorption approach. Advantages and drawbacks of both approaches are discussed.

[238] Polyvalent Hydrogen-Bonding Functionalization of Ultrathin Hyperbranched Films on Polyethylene and GoldD. E. Bergbreiter, G. L. Tao, J. G. Franchina and L. SussmanMacromolecules 34(9) (2001), 3018-3023

Hyperbranched poly(acrylic acid) and poly(N- isopropylacrylamide) grafts on gold and polyethylene films are good substrates for a new, mild hydrogen-bond-based grafting method. In this chemistry, a hydrogen-bond-donating or - accepting hyperbranched graft couples to a polymeric acceptor or donor in ethanol solution through multiple hydrogen-bonds. In contrast to plain surface-functionalized polyethylene films or to functional monolayers on gold, hyperbranched grafts are more capacious and more tenacious in this hydrogen-bond graft chemistry. Substantial amounts of polyacrylamide or poly(acrylic acid) reversibly bind to the hyperbranched graft based on IR spectroscopy, fluorescence spectroscopy, and ellipsometry. Fluorescence studies using dansyl-labeled soluble polymers that were hydrogen-bonded to hyperbranched grafts show that these hydrogen-bond assemblies are stable to prolonged extraction with protic and aprotic solvents. These interfacial hydrogen-bonded assemblies do not readily disassemble unless the hydrogen-bond donor is deprotonated with base.

[239] Ordered Polyelectrolyte Multilayers - 1 - Mechanisms of Growth and Structure Formation - A Comparison with Classical Fuzzy MultilayersX. Arys, A. Laschewsky and A. M. JonasMacromolecules 34(10) (2001), 3318-3330

The growth and structuring of polyelectrolyte self-assemblies (so-called ''multilayers'') made from a lyotropic ionene and a strong polyelectrolyte are examined in depth using X-ray reflectometry among other techniques. We show that highly ordered polyelectrolyte films may be obtained, consisting of a regular lamellar nanostructure extending over considerable distances in the films, with preferential orientation of chain fragments occurring in the films. This is in marked contrast with classical, ''fuzzy'' multilayers, for which no internal structure was reported so far. From our set of results, including a comparison of the structures of ''multilayers'' and bulk complexes, we propose that three mechanisms govern film growth and structuring: adsorption of the polyelectrolyte (governed by electrostatic balance), diffusion of the polyelectrolyte into the previously adsorbed film (which is the blurring step), and surface-constrained complexation between the polyanion and the polycation resulting from the mixing due to diffusion. Depending on whether the polyelectrolytes are capable of forming structured complexes or not, the self- assembled film will present different levels of internal organization. These findings have important implications for the general understanding of electrostatic self-assembly and for possible applications therefrom.


[240] Anomalous Adsorption of Polyelectrolyte LayersS. Y. Park, C. J. Barrett, M. F. Rubner and A. M. MayesMacromolecules 34(10) (2001), 3384-3388

We study the adsorption of polyelectrolytes onto oppositely charged surfaces as the surface charge density is varied while keeping the polyelectrolyte charge density fixed. As observed previously from multilayer adsorption studies,(1,2) nonmonotonic adsorption behavior is obtained in the intermediate surface charge density regime, with anomalously thick ''supermonolayers'' transitioning to molecularly thin lavers over a small range of surface charge densities. A simple adsorption model is introduced to explain these findings, in which the surface is characterized by discrete and fully compensated adsorption sites.

[241] Adsorption of Polyelectrolytes at Oppositely Charged SurfacesA. V. Dobrynin, A. Deshkovski and M. RubinsteinMacromolecules 34(10) (2001), 3421-3436

We have developed a scaling theory of polyelectrolyte adsorption at an oppositely charged surface. At low surface charge densities, we predict two-dimensional adsorbed layers with thickness determined by the balance between electrostatic attraction to the charged surface and chain entropy. At high surface charge densities, we expect a 3-dimensional layer with a density profile determined by the balance between electrostatic attraction and short-range monomer-monomer repulsion. These different stabilizing mechanisms result in a nonmonotonic dependence of the layer thickness on the surface charge density. For adsorption of polyelectrolyte chains from salt solutions, the screening of the electrostatic repulsion between adsorbed polyelectrolyte chains results in large overcompensation of the surface charge for two-dimensional adsorbed layers. At higher salt concentrations this overcompensation of the surface charge by the 2-d adsorbed layer is independent of the original surface charge and depends only on the fraction of the charged monomers on the polyelectrolyte chains and increases with ionic strength. The polyelectrolyte surface excess in 3-d adsorbed layers increases at low ionic strength and decreases at higher ionic strength.

[242] Polyelectrolyte Multilayers Containing a Weak Polyacid - Construction and DeconstructionS. T. Dubas and J. B. SchlenoffMacromolecules 34(11) (2001), 3736-3740

The growth of multilayers made from a combination of a weak polyacid and a strongly dissociated polycation is studied as a function of salt concentration and molecular weight. Film thickness reaches a maximum at around 0.3 M salt and then decreases quickly. Preformed multilayers are shown to decompose rapidly and, for high molecular weights, completely when exposed to aqueous solutions of NaCl of concentration >0.6 M. The apparent dissociation of multilayer polyelectrolyte complexes is due to competition for polymer/polymer ion pairs by external salt ions. Similar experiments aimed at decomposing multilayers by protonating the weak acid, thus decreasing polymer/polymer interactions, lead to incomplete loss of polymer, probably due to additional hydrogen bonding from the protonated weak acid. A model based on ion exchange/swelling of multilayers is used to explain their stability and permeability as well as the dependence of film thickness on salt concentration and type.

[243] Layer-by-Layer Preparation of Zeolite Coatings of Nanosized CrystalsV. Valtchev and S. MintovaMICROPOROUS MESOPOROUS MAT 43(1) (2001), 41-49

In this contribution a new approach for preparation of zeolite films is described. Layer-by-layer self-assembly technique was employed for the preparation of zeolite coatings on negatively charged polystyrene beads, The procedure consists of two basic steps. In the first the beads were surface modified in order to facilitate adsorption of zeolite nanocrystals. A monolayer of crystals are then adsorbed on the bead surface, The number of deposition cycles control the thickness of zeolite coatings. Following this approach zeolite coatings of LTA, FAU, BEA and MFI type zeolites were prepared. Zeolite/polystyrene composites and the corresponding hollow zeolite spheres were characterized by SEM, TEM, X-ray diffraction, FTIR and thermogravimetric analyses. (C) 2001 Elsevier Science B.V. All rights reserved.


[244] Tuning the Performance of Layer-by-Layer Assembled OLEDs by Controlling the Position of Isolating Clay Barrier SheetsM. Eckle and G. DecherNanoletters 1 (2001), 45-49

We have fabricated organic light emitting diodes (OLEDs) based on poly(p-phenylenevinylene) (PPV) and poly(methacrylic acid) (PMA), including an isolating layer composed of montmorillonite. We show that the single clay layer influences the behavior of the devices, lowering current densities and increasing light output in comparison with pure polymer systems. The subnanometer positioning of this isolating barrier within the active medium with respect to both electrodes, which is easily controlled by the deposition sequence, plays a key role for the electrooptical properties of the diodes.

[245] Self-Assembly of Small Molecules - An Approach Combining Electrostatic Self-Assembly Technology with Host-Guest ChemistryY. J. Zhang and W. X. CaoNew J. Chem. 25(3) (2001), 483-486

A fluorescence probe study, surface tension and dye solubilization tests indicate that the water-soluble calixarene, 5,11,17,23,29,35,41,47-octosulfonato- 49,50,51,52,53,54,55,56-octododecyloxycalix[8]arene (1(8)-C-12) acts as a ''unimolecular'' micelle in water. By forming guest- host-type complexes with 1(8)-C-12, lipophilic dyes, such as methyl yellow (MY), p-hydroxyazobenzene (HAB) and 1-(p- phenylazophenylazo)-2-naphthol (Sudan III), dissolve in aqueous solution. By dipping a charged substrate in the 1(8)-C-12-dye solution and a cationic polyelectrolyte solution alternately, these small molecular dyes were successfully self-assembled into multilayer films.

[246] Fabrication of Microgratings on the Ends of Standard Optical Fibers by the Electrostatic Self-Assembly Monolayer ProcessF. J. Arregui, I. R. Matias, K. L. Cooper and R. O. ClausOptics Letters 26(3) (2001), 131-133

The electrostatic self-assembly monolayer process has been utilized for what is believed to be the first time to deposit quarter-wavelength stacks on the end faces of cleaved and polished optical fibers. Standard multimode optical fibers as well. as single-made optical fibers were used as substrates with different coating materials to fabricate broadband filters, and the experimentally measured spectral responses of these devices are shown. These optical filter structures were employed to develop chemical sensors that use an unperturbed reference wavelength to normalize the output signal. (C) 2001 Optical Society of America.

[247] Effect of pH on the Preparation of Self-Assembled Films of Poly(O-Ethoxyaniline) and Sulfonated LigninL. G. Paterno and L. H. C. MattosoPolymer 42(12) (2001), 5239-5245

Self-assembled films of Poly(o-ethoxyaniline) (POEA) doped with HCl alternated with sulfonated lignin (SL) were successfully produced under different pHs and their kinetics of formation studied. The adsorption at lower pi-Is is faster due to the greater electrostatic attraction between the POEA and the SL covered substrate, but a lower amount of POEA is deposited due to ch;uge repulsion of additional POEA chains and conformational steric hindrance. At higher pHs the adsorption of POEA cakes longer but it is greater due to the contribution of hydrogen bonding interactions, lower charge repulsion between POEA chains and a more compact polymer conformation. Adsorption of POEA/SL multilayers could be carried out in different types of substrates. Atomic force microscopy (AFM) employed to investigate the morphology of the alternated layers showed that POEA layers exhibited a granular rough aspect, while SI, layers presented a much smoother surface. (C) 2001 Elsevier Science Ltd. All rights reserved.

[248] Photovoltaic Cells Based on Ionically Self-Assembled NanostructuresT. Piok, C. Brands, P. J. Neyman, A. Erlacher, C. Soman, M. A. Murray, R. Schroeder, W. Graupner, J. R. Heflin, D. Marciu, A. Drake, M. B. Miller, H. Wang, H. Gibson, H. C. Dorn, G. Leising, M. Guzy and R. M. DavisSynthet. Metal 116(1-3) (2001), 343-347


We use the technique of ionically self-assembled monolayers (ISAMs) to produce photovoltaic devices of well-controlled thickness and composition. The ISAM nanostructure fabrication method simply involves the alternate dipping of a charged substrate into aqueous cationic and anionic solutions at room temperature. We have employed several approaches to combine the tetrahydrothiophenium precursor of poly(para-phenylenevinylene) (PPV) with fullerenes and other organic materials. We apply modulation spectroscopy for the electrooptical characterization of the ISAM-devices. The modulation frequency dependence of the photocurrent can be assigned to the influence of trapped charges taking Dart in the photovoltaic process. (C) 2001 Published by Elsevier Science B.V.

[249] Electrostatic Self-Assembly as a Means to Create Organic Photovoltaic DevicesM. F. Durstock, B. Taylor, R. J. Spry, L. Chiang, S. Reulbach, K. Heitfeld and J. W. BaurSynthet. Metal 116(1-3) (2001), 373-377

Recently, there has been a significant amount of work done on making photovoltaic devices (solar cells) from thin films of conjugated polymers and other organic systems. The advantages over conventional inorganic systems include the potential to create lightweight, flexible, and inexpensive structures. The challenge, however, has been to create more highly efficient devices. To date, the primary photovoltaic device mechanism that has been utilized is that of photoinduced charge transfer between an electron donor and acceptor. In this study, similar photovoltaic devices are fabricated using a water-based electrostatic self-assembly procedure, as opposed to the more conventional spin-coating and/or vacuum evaporation techniques. In this process, layers of oppositely charged species are sequentially adsorbed onto a substrate from an aqueous solution and a film is built up due to the electrostatic attraction between the layers. The technique affords molecular level control over the architecture and gives bilayer thickness values of the order of tens of angstroms. By repeating this process a desired number of times and utilizing different cations and anions, complex architectures can be created with very accurate control over the thickness and the interfaces. We have examined a number of systems built from a variety of components including a cationic PPV precursor, functionalized Co,, and numerous other polyelectrolytes. We report on the device characteristics of these films and on the overall applicability of this technique to the fabrication of photovoltaic devices. Published by Elsevier Science B.V.

[250] Highly Efficient Energy and Charge-Transfer in Thin Self- Assembled Multilayered Polymer-FilmsH. L. Wang, D. W. Mcbranch, R. J. Donohoe, S. Xu, B. Kraabel, L. H. Chen, D. Whitten, R. Helgeson and F. WudlSynthet. Metal 121(1-3) (2001), 1367-1368

We report the synthesis and characterization of multilayer self- assembled polymer films made from a water-soluble conjugated polymer, poly(2,5-methoxy-propyloxy sulfonate phenylene vinylene) (MPS-PPV). We observe a red shift, of both the absorption and fluorescence spectra with increasing numbers of active MPS-PPV layers. We attribute this red shift to changing polymer conformation and efficient energy transfer. Upon adding a water-soluble C-60 Or C-60-VBA copolymer top layer, the luminescence spectrum is strongly quenched due to charge transfer. The estimated charge transfer quantum efficiency from PL quenching is similar to 95%. We discuss in detail the unidirectional energy transfer followed by charge transfer in the self-assembled multilayered films.

[251] Multilayers Prepared from Electronically Conducting Conjugated PolyelectrolytesJ. Lukkari, A. Viinikanoja, M. Salomaki, T. Aaritalo and J. KankareSynthet. Metal 121(1-3) (2001), 1403-1404

Electroactive polyelectrolyte multilayers have been prepared using a water-soluble poly-3-(3'thienyloxy)propanesulfonate CP3TOPS). In aqueous solutions the properties of the multilayers were typical to polythiophene films. Charge transfer rate measurements indicate that P3TOPS can penetrate through ca. 4 polyelectrolyte bilayers.

[252] Photovoltaic Interface Modification via Electrostatic Self- AssemblyJ. W. Baur, M. F. Durstock, B. E. Taylor, R. J. Spry, S. Reulbach and L. Y. ChiangSynthet. Metal 121(1-3) (2001), 1547-1548

The device efficiency of PPV-C-60 based photovoltaic devices has been substantially increased by increasing the interfacial area between the electron donor and acceptor layers. Electrostatic Self-Assembly (ESA) provides a means


to deposit thin films of electroactive materials with a very controlled thickness and has shown usefulness in modifying physical and electrical interfaces. in this study, we attempt to control the effective interfacial area by modifying the interface between the PPV electron donor and C-60-based electron acceptor with molecularly blended ESA bilayers of PPV and derivatized C-60 If is observed that with only 2 bilayers of (PPV/C-60(-)) a 3-fold increase in device efficiency is obtained. Thus, ESA films offer promise for the nanoscaled modification of interfaces in organic-based photocells.

[253] Photocarrier Generation Quantum Yield for Ionically Self- Assembled MonolayersT. Piok, R. Schroeder, C. Brands, J. R. Heflin, G. Leising and W. GraupnerSynthet. Metal 121(1-3) (2001), 1589-1590

We have fabricated photovoltaic cells from organic donor/ acceptor couples arranged as ionically self assembled monolayers, Making use of the morphological control on the nanometer level we were able to study the influence of the device structure and layer composition on the quantum yield of charge carrier photogeneration, The photoluminescence quenching and the photocurrent spectra reveal sample composition, charge carrier photogeneration and transport properties independently.

[254] Microring Light-Emitting Devices with Self-Assembled Multilayer Structures Based on Poly(P-Phenylene Vinylene)ST. Fujisawa, T. Sonoda, R. Ootake, A. Fujii and K. YoshinoSynthet. Metal 121(1-3) (2001), 1739-1740

Periodic multilayer structures of poly(p-phenylene vinylene)s have been fabricated by a self-assembly method on flat surfaces and round surfaces of optical fibers. Alternating multilayers consisting of poly(1,4-(2-(5-carboxypentyloxy)-5- methoxyphenylene)vinylene) and poly(p-phenylene vinylene) have been adsorbed onto the positively charged substrates and the optical properties have been studied. The periodic multilayers with microring geometry have also been fabricated around the quartz fibers, and the optical properties and yellow electroluminescence from a light-emitting device with microring geometry have been investigated.

[255] Alternate Deposition of Horseradish-Peroxidase and Bipolar Pyridine Salt on the Solid-Surface to Prepare Electrocatalytically Active Enzyme Thin-FilmW. J. Li, M. Xian, Z. C. Wang, C. Q. Sun and M. Y. ZhaoThin Solid Films 386(1) (2001), 121-126

Horseradish peroxidase (HRP)-containing multilayer films have been fabricated by alternate deposition with bipolar pyridine salt (PyC6BPC6Py) on the surface of gold electrode derivatized by 3-mercapto-1-proponesulfonate monolayer. The driving force of forming the multilayer structures is the electrostatic interaction between the negatively charged HRP and the positively charged PyC6BPC6Py. The assembly process was monitored by ultraviolet-visible spectroscopy on quartz slides. The electrochemical behavior of the enzyme electrode showed that the multilayer film was stable and electroactive. The diffusing mediator, methylene green in solution as an electron shuttle, was able to Transfer electrons successfully between the active center of the immobilized HRP and the electrode surface. Its potential application as amperometric sensor for hydrogen peroxide is anticipated. (C) 2001 Elsevier Science B.V. All rights reserved.

[256] Self-Assembled Inorganic/Organic Composite Superlattice Thin- Films with Photochromic PropertiesZ. H. Chen, Y. Ma and J. N. YaoThin Solid Films 384(2) (2001), 160-165

A multicomposite WO3/4,4'-BPPOBp self-assembled multilayer (SAM) film was fabricated by the consecutive self-assembly of WO, and 4,4'-BPPOBp on 3-aminopropyl-triethyoxysilane (APS) modified quartz or silicon substrate by a polyelectrolyte (PE) approach. A well-ordered superlattice structure, d-spacing 0.694 nm, was identified by X-ray diffraction and X-ray reflection techniques. The SAM film shows fine photochromic properties. (C) 2001 Elsevier Science B.V. All rights reserved.


[257] 2-Step Assembly Technique for Preparation of Polymer-Particle Composite FilmsH. HattoriThin Solid Films 385(1-2) (2001), 302-306

Two-step assembly (TSA) technique for preparation of polymer- particle composite films is presented. The TSA process consists of coating a polyelectrolyte onto a substrate and dipping the coated substrate in a particle suspension. The previously coated polyelectrolyte acts as a particle aggregation promoter, in other words, as an adhesive for particles. Diffusion and adsorption of the polyelectrolyte are important behaviors for this process. Preparation of composite films consisting of commercially available polyelectrolytes such as poly(diallyldimethylammonium chloride) (PDDA) and colloidal silica (SiO2) or titania (TiO2) particles were demonstrated. The composite films were porous and their thickness depended on the thickness and the molecular mass of previously coated polyelectrolyte, treatment time, and the concentration of suspension. Some PDDA-SiO2 composite films with 190 nm SiO2 particles had colloidal crystal domains and reflected visible light. (C) 2001 Elsevier Science B.V. All rights reserved.


Dear Colleagues, - Department of Chemistry [FSU] 2000-2001.doc · Web viewDear Colleagues, here is,...

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