Stimuli Responsive Polymeric Colloids and Advanced...

27th ECIS Conference 1 - 6 September 2013, Sofia, Bulgaria

Stimuli Responsive Polymeric Colloids and Advanced Materials

John Texter*

Coatings Research Institute, Eastern Michigan University, Ypsilanti, MI 48197, USA * - [email protected]

Stimuli responsiveness in polymer design is burgeoning and is providing basis for diversely new and advanced materials.1,2 These advanced materials include switchable porosity in membranes and coatings,3 switchable particle formation and thermodynamically stable nanoparticle dispersions,4 mechanicochemically-coupling polymers that provide directed mechanical stress in response to intensive fields,5,6 and switchable stabilization and compatibility of nanomaterials in changing environments, among others.7 The growth of ionic liquid applications and the concomitant incorporation of ionic liquids into polymeric materials have resulted in a plethora of new polymers based on the imidazolium group. Such polymers exhibit all of the above-articulated properties and can be distinguished as a cl ass of cationic polyelectrolytes.1,2

In water and other solvents the interaction strength of various anions with the imidazolium group follows a Hofmeister series that imparts highly solvophilic character to highly solvophobic character depending on the particular anion-imidazolium ion-pair. We show that the dynamic range of these interactions spans 104 in concentration, and is the basis for tuning various stimuli responsive interactions. The most fundamental effect is how these interactions affect polymer solubility. Switching solubility from high to low forms a basis for advanced dispersion phase transfer. It also provides approaches to switching between transparent gels and open cell porous materials. These effects are shown to be applicable to the formation of thin films by nanolatexes, and that subsequently can be transformed into porous membranes. Another exciting application area is the incorporation of such imidazolium groups into block copolymers. Block copolymers8 and nanolatexes3 have been demonstrated to be excellent stabilizers for nanocarbons and other materials in water. When used by adsorption from solution, these nanolatexes behave as osmotic spheres and the triblocks as osmotic brushes; both classes of polymer are shown to immunize against Debye-Hückel charge screening induced coagulation. Particularly interesting are demonstrations that di-stimuli responsive diblocks can reversibly form thermodynamically stable dispersions.

The highly stable and concentrated nanocarbon dispersions in water are also shown to provide high performance new materials, including templated coatings with very high thermal conductivities (0.8 to 3 kW/m/K).9 Waterborne graphene dispersions are shown to form optical-rheological fluids that become light reflecting in shear fields. These graphene dispersions are also used to demonstrate a new type of deposition/coating process based upon t he stimuli responsiveness of the stabilizing copolymer.

Fig. 1 Stimuli responsive pore gating


1. Yan, F; Lu, J; Texter, J. 2009. Advanced applications of ionic liquids in polymer science. Prog. Poly. Sci. 34, 431-448.

2. Texter, J. 2012. Anion responsive imidazolium-based polymers. Macromol. Rap. Com. 33, 1996-2014.

3. England, D; Tambe, N; Texter, J. 2012. S timuli-responsive nanolatexes – Porating films. ACS Macro Lett. 1, 310-314.

4. Tauer, K; Weber, N; Texter, J. 2009. C ore-shell particle interconversion with di-stimuli-responsive diblock copolymers. Chem. Commun. 45, 6065-6067.

5. Ma, X; Ashaduzzaman, Md; Kunitake, M; Crombez, R; Texter, J; Slater, L; Mourey, T. 2011. Stimuli responsive poly(1-[11-acryloylundecyl]-3-methyl-imidazolium bromide) – dewetting and nanoparticle condensation phenomena. Langmuir 27, 7148-7157.

6. Ma, X; Crombez, R; Ashaduzzaman, Md; Kunitake, M; Slater, L; Mourey, T; Texter, J. 2011. Polymer dewetting via stimuli responsive structural relaxation – Contact angle analysis. Chem. Commun. 47, 10356-10358.

7. Page, K; England, D; Texter, J. 2012. Capturing nanoscale structure in network gels by microemulsion polymerization. ACS Macro Lett. 1, 1398-1402.

8. Texter, J; Arjunan Vasantha, V; Maniglia, R; Slater, L; Mourey, T. 2012. Triblock copolymer based on po ly(propylene oxide) and poly(1‐ [11‐ acryloylundecyl]-3‐ methyl-imidazolium bromide). Macromol. Rap. Com. 33, 69-74.

9. Texter, J; Ager, D; Arjunan Vasantha, V; Crombez, R; England, D; Ma, X; Maniglia, R; Tambe, N. 2012. Advanced nanocarbon materials facilitated by novel stimuli-responsive stabilizers. Chem. Lett. 41, 1377-1379.


Molecular Modeling of Ion Atmosphere of Colloidal Systems

Hitoshi Washizu 12*, Tomoyuki Kinjo 12, Hiroaki Yoshida12

1 – Toyota Central R&D Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi 477-0140, Japan 2 – Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University,

Kyotodaigaku Katsura, Nishikyo-ku, Kyoto 615-8520, Japan * - [email protected]

Theoretical understanding of colloidal systems is extremely difficult even if a simple model is used for a macroion. This is because the internal motion of the macroion, the concentrations of small mobile ions, the long-range coulomb potential, and the solvent velocity are coupled with each other through essentially nonlinear equations. Coarse-grained simulations are useful tools to analyze the mechanism dynamics of colloidal systems. The importance of the system may due to the nonuniformity of the small ion distribution interacting with each other over the wide space of the solution. On the other hand, if the motion of solvent molecules is neglected, the effect of solvent flow that may play a large role cannot be incorporated. Also the important effect of solvent hydration cannot be discussed. A simulation involving coupling the dynamics of a vast ion atmosphere, the effect of local solvation around each of the ions, and macroscopic friction should be constructed to overcome the difficulty. Multiphysical course-grained simulators for molecular scale to meso-scale dynamics are under construction.

First, the Monte Carlo Brownian Dynamics method1 is used to simulate the nature of polyelectrolyte brushes. The polyions are grafted to the surface at an equal pitch. Long-range Coulomb interactions are coarse-grained by the modified Particle-Particle Particle-Cell method. For a flexible polyion model, a bond a nd bond angle degree of freedom is adopted. Charge densities of the polyions are an essential topic concerning the friction of a polyelectrolyte brush. In order to understand the charge density effect, the linear charge density parameter of the polyion is set to 0.0 to 2.0 in order to discuss the Manning's counterion condensation theory. The effect of added salts has been observed as the shrinkage of the brush heights.

In order to discuss the friction behaviours in these systems, improvements in the simulator are then needed to include the effect of the solvent. First, the solvent model is made to include the solvation effect of polymers and counter-, and co-ions. In the framework of dissipative particle dynamics, polarizability of a set of solvent molecules is described as oscillators. The solvent flow is then included by calculating the Brownian particles by Langevin dynamics and the solvent flows by the Lattice Boltzmann method. In this method, the dynamics of a huge amount of small ions are enabled by treating each Brownian particle as a point described by a Stokes-source. These methods essentially treat ions as particles. In order to treat macroscopic phenomena, a multiphysical simulator based on continuum equations of ion distribution, solvent flow, and electric fields is created. Distributions of small ions are treated by Nernst-Planck equations to treat transitional and non-bulk ion distribution.

Literature:

1. H. Washizu, K. Kikuchi, 2006, J. Phys. Chem. B, 110 (6), 2855-2861.

Acknowledgements:

The present work was partially supported by MEXT program "Elements Strategy Initiative to Form Core Research Center" (since 2012), MEXT; Ministry of Education Culture, Sports , Science and Technology, Japan.


Designing eptide-based iomaterials: tructure and elated roperties

Laura Chronopoulou 1*, Simona Sennato 2, Federico Bordi 2, Andrea Barbetta 1, Mariella Dentini 1, Anna Rita Togna 3, Giuseppina Ines Togna 3, Cleofe Palocci 1

1 – Department of Chemistry, Sapienza University of Rome, Rome, Italy 2 – Department of Physics and CNR-IPCF, Sapienza University of Rome, Rome, Italy

3– Department of Physiology and Pharmacology Vittorio Ersparmer, Sapienza University of Rome, Italy

* - [email protected]

Recently, scientific as well as technological interest in the synthesis of novel peptide-based hydrogel materials have grown dramatically. Applications of such materials mostly concern the biomedical field with examples covering diverse sectors such as drug delivery, tissue engineering and production of scaffolds for cell growth, thanks to their biocompatibility and biodegradability. In this framework, we successfully explored the possibility of using microbial lipases to catalyze the synthesis in water of self-assembling peptides such as Fmoc-Phe3, that afforded self-supporting hydrogels able to promote microglial cells proliferation and NGF production (1). Our interest was then drawn by the possibility of using unconventional peptides, such as D-peptides, to enhance hydrogel in vivo stability. D, L and mixed D,L peptides formed β-sheet-based molecular structures, as evidenced by circular dichroism. Atomic Force Microscopy investigation on hydrogels deposited on m ica support evidenced a complex self-assembled network formed by nanofibers, whose structural details depend on the chirality of the peptide. The hydrogelators show the ability to form helical nanofibers within the hydrogels, and the chirality of the hydrogelators apparently dictates the handedness of the nanofibers. Thus, this new class of D-form self-assembling peptides has proven to be very versatile in fabricating novel supramolecular architectures and may have a wide range of applications in nanobiotechnology.

Fig. 1 Molecular hydrogelation (a), AFM image of Fmoc-D-Phe3 (b), with height profile of a single fiber (c) and a detail showing the handedness of some nanofibers (d).

Literature: 1. L. Chronopoulou, A.R. Togna, G. Guarguaglini, G. Masci, F. Bordi, F. Giammaruco, G.I.

Togna, C. Palocci 2012. Soft Matter 8: 5784-5790.


Osmotic ressure of olyacrylate alts olutions: imulations and xperiments

Joaquim Li 1*, Marie Skepö 1, Magnus Ullner 1, Bo Jönsson 1

1 – Division of Theoretical Chemistry, Department of Chemistry, Lund University * - [email protected]

Polyacrylate salts are widely used in daily life as well as in industrial processes. We use their adsorption properties and their swelling properties in diapers, concrete, cosmetics, and paper. A key parameter controlling the behaviour of all these systems is the osmotic pressure. The osmotic pressure will be linked to the aggregation and conformational extension of the polyacrylates, to their degree of ionisation and therefore will tell us a great deal about the molecular behaviour of the polymeric chains and their counterions. Here we present our progress in the measurements of the osmotic pressure of polyacrylate salts. We tried to improve the accuracy of the osmotic stress technique and used it for the measurement of the osmotic pressure of polyacrylates of varying length, at different pH and in the presence of different salts. We compare these measurements with coarse-grained Monte Carlo simulations of polyacrylate chains in the cell model. We find good agreement between simulations and experiments and discuss the significance and limitations of this agreement.

Fig. 1 Comparison between the simulated osmotic pressure and the experimental osmotic pressure of different sodium polyacrylate samples. The sizes of the polymers in the simulations are 256 and 64 monomers. The sizes of the polymers in the experiments are ~800, ~400 and ~80 monomers. For the longest polymer, the pH has been varied between 5.5 and 8.


Chain Exchange Dynamics in n-Alkane–PEO Soft Colloidal Model Systems

Lutz Willner1*, Thomas Zinn1, Matthias Amann1, Jörg Stellbrink1, Aurel Radulescu1, Marie-Soussai Appavou1, Dieter Richter1, Reidar Lund2, Peter Lindner3

1 Jülich Centre for Neutron Science (JCNS) & Institute for Complex Systems (ICS), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany.

2 Dept. of Chemistry, University of Oslo Postboks 1033 Blindern, 0315 Oslo, Norway.

3 Institute-Laue-Langevin (ILL), Grenoble, France. * - [email protected]

Block copolymers spontaneously self-organize into polymeric micelles when dispersed in a selective solvent. Micellar growth is primarily driven by the incompatibility of the insoluble block with the solvent and counterbalanced by unfavorable configurations of the chains in core and corona of the micelles. A n important prerequisite to reach a nd to attain equilibrium in micellar solutions is a continuous exchange of constituting chains between different micellar entities. In recent years time –resolved small angle neutron scattering (TR-SANS) turned out to be a very successful method to investigate chain exchange kinetics of block copolymer micelles. The TR-SANS technique relies on a specific labeling scheme, the so-called kinetic zero average contrast (KZAC) technique, where deuterated and proteated micelles are mixed in a solvent that is contrast matched with the average of the oppositely labeled h and d polymers. This technique has led to an understanding of fundamental kinetic processes as described in more detail in a recent review [1].

In this contribution we will present kinetic results on n-alkyl-PEO polymers (CnH2n+1-O-PEOx) in aqueous solution. The n-alkyl-PEOs can be considered as hybrids between low-molecular weight surfactants and block copolymers. We have studied kinetics varying the n-alkyl length (n=18, 21, 24, 27, 28, 30), the molecular weight of PEO, (x=5, 10, 20, 40 kg /mol at constant n=27) and temperature. In all cases we observed a first order kinetic process which is characterized by a single exponential relaxation function, R(t) ~exp(t/τ). It was found that the time scale for chain exchange extremely depends on the alkyl chain length, n, and temperature T, while increasing t he PEO chain length reveals only a moderate slowing down of the rate. Time temperature superposition reveals an Arrhenius type behavior where the characteristic times show a linear dependence for 1/T. Activation energies were deduced from Arrhenius plots. They depend linearly on n w ith an increment of ∆Ea~10 kJ/mol and reaches values of about 180 kJ /mol for n=30. In this contribution detailed experimental results will be presented and discussed in terms of the Halperin & Alexander scaling theory. Activation energies will be compared to values obtained by rheology on transient n etworks formed by similar telechelic PEOs.

Literature:

1 R. Lund, L.Willner, D. Richter Adv. Polym. Sci. 2013 in press. 2 A. Halperin, S. Alexander, Macromolecules 22, 2403 (1989).


Bulk and Interfacial Microreology

Francisco Ortega1*, Laura J. Bonales1, Armando Maestro1 , Nuria Mancebo1, Fernando Martínez-Pedrero1, José E. Fernandez-Rubio1, Raquel Chuliá1, Alma J. Mendoza1, Ramón G.

Rubio1

1Departamento de Química Física I, Universidad Complutense de Madrid, Ciudad Universitaria s/n Madrid, Spain


Micro and nanoreology [1,2] encompass a family of methods that uses micro- and nanoparticles as mechanical probes of the rheological behavior of soft materials. Microrheology presents several advantages over conventional mechanical rheology: smaller size samples (∼µL), use in heterogeneous samples (i.e. simultaneous measurement of several environments), use in situ (e.g. cells), high throughput screening capability and very small perturbation applied (in passive microrheology the thermal energy ∼KBT). The fact that the applied stress is very small is of great importance when dealing with interfacial systems which are very fragile soft materials.

We will discuss the experimental techniques [1,2] and the different procedures [1,3] used to extract the complex shear modulus from the microrheological experiments. In this discussion we will present results from two different 3D systems, agarose gel solutions and pluronic solutions, and several monolayers (quasi-2D systems) of surfactants and polymers.

Literature:

1. Waigh, T.A., 2005. Rep. Prog. Phys., 68:685. 2. Mason, T. G.; Weitz, D.A., 1995. Phys. Rev. Lett., 74:1250 3. Mason, T.G., 2000. Rheol. Acta, 39:371.

Acknowledgements: This work has been supported by MINECO under grant FIS2012-38231-C02-01, by COST Action CM1101 and by ESA under grants FASES and PASTA.


A any-body heory for olloid+ olymer ispersions

Jan Forsman*

Lund University, Box 12, 221 00 Lund, Sweden * - [email protected]

We utilize an effective potential theory, averaging over polymer configurations, so as to derive a many-body Hamiltonian between particles, in a colloid+polymer dispersion. Our theory utilizes a generalization of the Edwards-deGennes treatment of continuous chains. A recent extension is "good solvent" cases, wherein the polymer are modelled as hard-sphere chains. "Excess" many-body

interactions are handled by an expansion apporach, whereas the pair contribution enters via an explicit separate calculation. Scaling theory is adopted to ensure correct responses to changes of chain length and concentration. The many-body Hamiltonian can be utilized in Monte Carlo simulations, wherein only the particles are treated explicitly. These simulations are no more costly than corresponding ones for systems with pairwise interactions. Our treatment thus allows predictions, not only of phase diagrams, but also of structure, permitting direct comparisons with experimental SAXS/SANS data. Comparisons with computationally expensive simulations wherein the polymers are included explicitly, have shown that the theory is remarkably accurate. Examples are provided in the Figure below.

Colloid-colloid radial distribution functions, in colloid-polymer mixtures. Simulations using the many-body Hamiltonian (red) with implicit polymers,are compared with exact results from simulations where polymers are explicit (crosses). With longer chains, the latter simulations become unmanageable, while the former remain fast (minutes). The blue curves, displaying an exaggerated attraction, result if only the pair contribution to the Hamiltonian is included (implicit chains). Many-body effects are obviously important in these systems. Left graph: ideal chains (601-mers), and q=2. Right graph: hard-sphere monomer chains (176-mers), and q=1. Here, q is the ratio between the polymer radius of gyration, and the colloids radius.


Internal ynamics in onic icrogels in olution and in the dsorbed tate

Stefan Wellert1*, Marcel Richter1, Olaf Holderer2, Regine von Klitzing1

1 Stranski Laboratory, Technical University Berlin, Str. d. 17.Juni 124, 10623 Berlin, Germany 2 Jülich Centre for Neutron Science JCNS-FRMII, Lichtenbergstr. 1, 85747 Garching, Germany

* [email protected]

The physical properties of stimuli-responsive microgels still attract great interest in basic research and lead to a lively discussion of potential technical applications. A prominent example are systems, which undergo a temperature induced phase transition reflected in a discontinuous shrinking with increasing sample temperature. Microgel particles can be easily organized as ultra-thin films at solid surfaces, e.g. silicon single crystal surfaces. This leads to changes in the swelling behavior and shifts of the LCST with respect to the bulk phase. These findings raise the question how the interactions with the solid surface affect the internal structure and dynamics of the microgel particles. In a series of surface sensitive scattering experiments we addressed this question.

Here, we focus on n eutron spin echo spectroscopy (NSE) experiments in transmission and reflection geometry. Up to now, only few publications report NSE experiments on the internal dynamics in microgels. NSE provides access to the dynamics in the ns to ms time range on nanoscopic length scales. In particular, we studied the internal dynamics in ionic microgels in the bulk phase and in thin films adsorbed onto silicon surfaces. The internal dynamics in bulk phase samples was studied at different concentrations and degrees of protonation. Results of these measurements are compared to previously published work on neutral microgels and to our results on the internal dynamics in microgels in close-packed films adsorbed at silicon surfaces. Thin films of adsorbed microgels were studied for the first time by NSE under grazing incidence (GINSES) which uses evanescently scattered neutrons and therefore probes the near-surface dynamics in the adsorbed microgel films.


Aging Dynamics and Phase Behaviour of a Charged Colloidal Clay

Roberta Angelini 1*, Barbara Ruzicka 1, Emanuela Zaccarelli 2 , Giancarlo Ruocco1,3

1 – CNR-IPCF and Physics Department Sapienza University of Rome, I-00185 Italy 2 – CNR-ISC and Physics Department Sapienza University of Rome, I-00185 Italy

3 – Istituto Italiano di Tecnologie, Center for Life Nano Science, Sapienza, Rome, Italy * - [email protected]

The continuous interest in studying dynamics of colloidal systems has over the last decade led to a broadening of our knowledge on dynamical arrest and the glass transition. Many experiments performed on colloidal glasses and gels as well as theoretical and numerical simulation results aim at understanding the nature of the aging phenomena that are typical for systems with time evolving dynamics. Among these, colloidal clays, have recently emerged as complex fluid systems characterized by a peculiar aging dynamics. Here we investigate dilute suspensions of Laponite, an industrial synthetic clay made of nanometre-sized discotic platelets with inhomogeneous charge distribution and directional interactions. The anisotropy of the face-rim charge interactions, combined with the discotic shape of Laponite, produces a very rich phase diagram encompassing fluid, gel, glassy states [1,2] on varying colloidal volume fraction at fixed ionic strength. At low concentrations (CW


Oppositely Charged Polyelectrolyte/Surfactant Mixtures: Structural Origin of Changes in Viscosity

Ingo Hoffman1,2*, Bela Farago2, Michael Gradzielski1

1 – TU Berlin Institut für Chemie Stranski-Laboratorium für Physikalische und Theoretische Chemie

Straße des 17. Juni 124, Sekr. TC 7, D-10623 Berlin 2 – Institut Laue Langevin

6, rue Jules Horowitz F-38042 Grenoble Cedex 9


Systems composed of oppositely charged polyelectrolytes (PE) and surfactants show rich self-aggregation behavior that varies over a large size range and have many applications e.g. in cosmetics, detergency and drug delivery [1]. Mixtures of the cationic polyelectrolyte JR 400 with anionic surfactants in the semi-dilute regime with a slight excess of polymer charges form highly viscous network structures, with their viscosity increasing by 3-4 orders of magnitude as compared with the pure polymer solution, while mixtures with excess surfactant charges form solutions with viscosities even below those of the polymer solution [2,3].

With the help of neutron scattering, namely small-angle neutron scattering (SANS) and neuton spin-echo (NSE), we have been able to track the structural origins at the meso scale responsible for the remarkable changes in the macroscopic behavior of these solutions. As neutrons allow for an easy variation of the contrast simply by changing the isotopic composition, it is possible to study the individual components of the sample, thereby gaining insights difficult to acquire with other methods. While SANS observes the structure of solutions, NSE monitors the dynamics on a time scale of nano seconds and allows to investigate the behavior of the PE in the aggregates. It is observed that mixed rod-like aggregates are formed in the PE excess part of the phase diagram. However, these aggregates are still existent if an excess of surfactant is added and the origin of the change in macroscopic behavior is more subtle.

In summary, we studied the mesoscopic structure and dynamics of oppositely charged PE/surfactant complexes with both an excess of surfactant and PE. Using different contrasts, we gained an understanding of the role of the individual components and the structural changes at the mesoscale responsible for the changes in macroscopic viscosity.

Literature:

1. L. Chiappisi, I. Hoffmann, M. Gradzielski, 2013. Soft Matter, 9: 3896-3909 2. I. Hoffmann, P. Heunemann, S. Prévost, R. Schweins, N.J. Wagner and M. Gradzielski, 2011. Langmuir 27: 4386–4396 3. I.Hoffmann, S. Prévost, M. Medebach, S. Rogers, N. J. Wagner, M. Gradzielski, 2011. Tenside, Surfactants, Deterg 48: 488-494


Electro-optics of olyelectrolyte ultilayers on olloidal articles

Viktoria Milkova *, Kamelia Kamburova, Tsetska Radeva

Institute of Physical Chemistry, Bulgarian Academy of Sciences * - [email protected]

Polyelectrolyte multilayer films made by self-assembly of oppositely charged polymers onto submicron particles are promising systems for applications in fields as biomaterial coatings, drug delivery systems, electrocatalysis, electrochemistry [1]. The structure, stability and electrical properties of the multilayer films are crucial for all the envisaged applications.

We demonstrate the advantages of electro-optics for in situ investigation of multilayer films on non-spherical colloidal particles. The electro-optical signal is related to the electrical moment orientation mechanism, which in turn reflects the electrical double layer features of the particles through their electrical polarizability. The electro-optical signal contains also information on the shape and size of the particles, which makes this technique useful for controlling the stability of colloidal systems during preparation of the multilayer films as well as for determination of the film thickness.

We present results for films made from synthetic and bio-polymers on particles of different shape: ellipsoids (β-FeOOH), rods (α-Fe2O3) and discs (indomethacin) [2,3]. Multilayer films are found to grow linearly or exponentially in dependence on t he charge density ratio of the polymers. In contrast to electrophoretic mobility, the electrical polarizability of the particles coated by multilayer films increases with the number of deposited layers, in agreement with the film thickness increase. Our results also showed that the electrical parameters of the last adsorbed polymer dominate the behavior of the whole film. We will discus potential applications of the encapsulated colloidal particles for controlled drug release and corrosion protection of steel.

1. echer G 1997 F uzzy nanoassemblies: toward layered polymeric multicomposites Science 247 1232-1237. 2. adeva Ts, Milkova V, Petkanchin I 2004 D ynamics of counterions in polyelectrolyte multilayers studied by electro-optics Colloids Surf. A: Physicochem. Eng. Aspects 240 27-34. 3. adeva Ts, Kamburova K 2007 Polypeptide multilayer films on colloidal particles: An in situ electro-optical study J. Colloid Interface Sci. 308 309-317.

Acknowledgements: The authors acknowledge the financial support of the projects BG 051PO001-3.3.06-0038 and X-1212.


Influence of Polymer Weight and Barrier Layers on Interdiffusion in Polyelectrolyte Multilayers

Peter Nestler1, Malte Paßvogel1, Olaf Soltwedel2, Ralf Köhler3 and Christiane A. Helm1*

1Institut für Physik, Greifswald University, D-17487 Greifswald, Germany 2 Max-Planck-Institut für Festko ̈rperforschung, 70569 Stuttgart, Germany

3Stranski-Laboratorium and Helmholtz Zentrum Berlin fu ̈r Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin, Germany


Polyelectrolyte multilayers are made from poly(diallyldimethylammonium) (PDADMA), poly(styrenesulfonate) (PSS), and deuterated PSS-d.[1] Each film consists of a protonated and a deuterated block. The films are annealed in 1 M NaCl and investigated with neutron reflectivity. During annealing the internal interface between both blocks broadens due to interdiffusion.

The PSS interdiffusion constant depends non-monotonically on the PDADMA molecular weight, a maximum is observed at 45 kDa, in contrast to polymer theory. The experiments suggest that PSS and PDADMA move as a complex. If one polycation layer in the film centre is branched poly(ethyleneimine) (PEI), then PEI serves as a diffusion barrier. Consistent with polymer theory, the diffusion constant through the barrier decreases monotonically with PDADMA molecular weight.

Fig. 1 Normalized neutron reflectivity curves (left) and corresponding SLD profiles (right) of a (PEI/PSS)1(PDADMA/PSS)8/(PDADMA/PSS-d)5 film, measured at 0% rh (preparation conditions: Mw,PDADMAC = 35 kD a, 0.1 M NaCl, T = 20 °C ). After preparation, the PEMs are immersed for the time indicated into 1 M NaCl solution at 20 °C and dried. For clarity, the reflectivity curves are shifted relative to each other by 1 order of magnitude.

Literature:

1. O. Soltwedel, P. Nestler, H.G. Neumann, R. Köhler, C.A. Helm; Macromolecules 45 (2012) 7995


“Sideways” Nanotechnology - Enzymatic Production of Colloidal Hierarchical Materials

Ben J. Boyd 1*, Stephanie Phan1, Wye-Khay Fong 1, Adrian Hawley2

1 – Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville Campus), VIC, Australia

2 – SAXS/WAXS beamline, Australian Synchrotron, Clayton, VIC, Australia * - [email protected]

Enzymatic production of nanostructures is utilized widely by nature to transform biological materials and promote self assembly, but is often ignored as an alternative to bottom up or top down assembly of nanomaterials. As one example, during the digestion of lipids in the gastrointestinal tract a variety of self-assembled structures may be formed transiently that eventually and inevitably result in micelle formation.

In this study, inspired by lipid digestion, the generation of stable hierarchically structured nanostructured particles with internal bicontinuous cubic structure from emulsions is triggered via enzymatic lipolysis of a short chain triglyceride additive to the main structure forming lipid. Structural aspects were elucidated using real time synchrotron small angle x-ray scattering, dynamic light scattering and cryoTEM (below). The concept of mixing enzymatically labile and inert lipid substrates has not previously been harnessed for the deliberate selection of such self assembly structures. Through design of specific mixtures that transit from unstructured emulsions to highly structured dispersed liquid crystalline particles, new low energy methods to generate particles such as cubosomes and hexosomes are achieved. This new route to stabilised internally structured particles holds promise across the pharmaceutical, agricultural and food technology fields.

Fig. 1 Transformation from emulsion to hierarchically structured cubosomes using enzymatic trigger


The ole of esicles in the elling of ilute queous ixtures ontaining urfactant and atty lcohol

F. Grewe 1*, F. Polzer 2, G. Goerigk 3, S. Eriksson 4, D. Topgaard 4, C. Schmidt 1

1 – Department Chemie, Universität Paderborn, Germany 2 – Institut für Physik, Humboldt-Universität zu Berlin, Germany

3 – Helmholtz-Zentrum Berlin, Germany 4 – Physical Chemistry, Lund University, Sweden


Aqueous mixtures containing surfactant and alcohol can self-assemble into a w ide variety of liquid crystalline structures [1,2]. They often have gel-like properties and are applied in pharmaceutical, cosmetical, personal care, laundry, and food products [1-3]. The gel-like character may persist at high dilution, even at water concentrations higher than 90 wt %. The focus of our research lies on the investigation of the structure of the model system consisting of cetyl alcohol (CA), sodium dodecyl sulfate (SDS) and water [1]. A series of samples with a constant amount of water of 97 wt. % and a varying ratio of SDS to CA with a total mass of 3 wt. % was investigated. As for many colloidal systems, the processing parameters like temperature and shear rate have a large influence on the structure of the emulsion, which is not in thermodynamic equilibrium. Therefore, reproducible conditions for sample preparation must be chosen. The range of concentrations where gels are formed was identified and the structure of the gel-forming emulsions was investigated using a variety of different techniques, including rheology, electron microscopy, scattering techniques, NMR spectroscopy and diffusometry. By means of transmission electron microscopy and very small angle neutron scattering the gels were found to consist of uni- and multilamellar vesicles. Since the gels contain high amounts of the fatty alcohol, which has a small head group, lamellar structures were expected. The formation of vesicles is due to the shear applied during the mixing procedure [4,5]. Since the alkyl chains of CA are rigid at room temperature the vesicles are very stable. We propose that the gel property of the system is caused by the jamming of the vesicles, which prevents the system from flowing. A change of the surfactant parameter or the distance between bilayers may break the gel.

Literature:

1. R. J. Goetz and M. S. El-Aasser, 1990. Dilute phase behavior of cetyl alcohol, sodium lauryl sulfate, and water. Langmuir 6: 132-136.

2. T. S. Awad, E. S. Johnson, A. Bureiko and U. Olsson, 2011. Colloidal structure and physical properties of gel networks containing anionic surfactant and fatty alcohol mixture. Journal of Disperion Science and Technology 32: 807-815.

3. L. L. Schramm, E. N. Stasuik and D. G. Marangoni, 2003. Surfactants and their applications. Annual Reports Section C 99: 3-48.

4. O. Diat, D. Roux and F. Nallet, 1993. Effect of shear on a lyotropic lamellar phase. Journal de physique II 3: 1427-1452.

5. M. Bergmeier, H. Hoffmann and C. Thunig, 1997. P reparation and properties of ionically charged lamellar phases that are produced without shearing. Journal of Physical Chemistry B 101: 5767-5771.


Hydrogels with anoparticle ross-linkers for agnetic ensing of hemical hanges

Susanne van Berkum1, Albert P. Philipse1 and Ben H. Erné1*

1 – Van ’t Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, Utrecht University


To detect chemical changes in aqueous media using a m agnetic sensor, we develop hydrogels with embedded magnetic nanoparticles. Our gels are currently based on poly-acrylic acid, so that they can be made to swell or to shrink at constant temperature via a change in pH. Homogeneous ferro-hydrogels are prepared under chemical conditions where aggregation of the magnetic nanoparticles is minimized and they act as cross-linkers in the polymer network. The frequency-dependent magnetic properties of the ferro-hydrogels are strongly dependent on t he type of magnetic nanoparticles used, which affects the rapidity of Néel relaxation of the magnetic dipole inside the nanocrystals. With magnetite nanoparticles of a few nanometers, the magnetic relaxation at 50 kHz is almost as strong as when the particles are in colloidal dispersion in a liquid. Magnetite particles of 20 nm or cobalt ferrite particles lead to ferrogels with magnetic remanence, whose permanent magnetic field can be detected with a Hall sensor. The presentation will include aspects of chemical preparation, rotational arrest of the nanoparticles, time-dependent swelling and shrinking, and the detection of magnetic fields from ferro-hydrogels.


Time-limitable Hydrogels Controlled by Peptide Self-assembly

Nobuyuki Higashi 1*, Yuji Nikaido 1, and Tomoyuki Koga 1

1 Department of Molecular Chemistry and Biochemistry, Faculty of Science and Engineering, Doshisha University, Kyotanabe, Kyoto 610-0321, Japan


Hydrogels are networks of polymer chains with a large amount of water. Their water-swollen structures offer excellent biocompatibility and flexibility similar to natural tissue necessary to apply as biomaterials. Recent dramatic developments of this research field have enabled the construction of a wide variety of hydrogels with unique properties such as stimuli-responsive hydrogels and hydrogels with high mechanical property. However, there is no report about the hydrogels acted only for a limited period without any external-stimuli. We report herein for the first time a new class of intelligent hydrogel fabricated by self-assembling three-armed peptides (1n) t hat undergoes gel-to-sol transition in response to time under a physical condition. The peptides consist of short collagen-mimetic chains (Gly-Pro-Hyp triplet repeat, n = 5 or 6) linking a central lysine-template through flexible spacer as shown in Fig. 1a. These peptides were prepared by means of solid-phase synthesis with Fmoc chemistry and characterized by 1H-NMR and MALDI-TOFMS. Analyses of the conformation and self-assembling properties of the peptides in aqueous solutions were performed by using circular dichroism (CD) spectroscopy, vapour pressure osmometry and fluorescent resonance ernergy transfer experiment. With CD study, the peptides 1n in dilute solutions are found to take triple helices at lower temperature (4 °C) and exhibit transition from helix to random coil with elevating temperature. The transition temperature Tm depends strongly upon t he peptide sequence and the chain length (n). With condensing the solutions up t o 6 w t%, formation of triple helix structure intermolecularly triggers formation of metastable self-assembled fibrillar network, which leads to gelation in water at 4 °C. Interestingly, we found out that these hydrogels transformed spontaneously to sols after a prescribed period under a constant physical condition. Spontaneous transfer from the self-assembling form to thermodynamically favored dimeric form, which occurs without a loss of triple helix structure, causes dissolution of the gel (Fig. 1b). Furthermore, lifetime of such hydrogel can be controlled by manipulating the stability of the triple helix based on amino acid sequence. These time-limitable hydrogels using metastable assemblies offer novel design principle for functional soft-materials, and also have potential in biological applications.

(a) (b)

Fig. 1 (a) Molecular structures of collagen-mimetic peptides. (b) Time-dependence of 16- hydrogel (6 wt%) at a constant temperature of 4 °C.


Fine-tuning the tructure of timuli-responsive olymer ilms by emperature and ydrostatic ressure

Matthias Reinhardt 1*, Joachim Dzubiella 2, Marcus Trapp 3, Philipp Gutfreund 4, Martin Kreuzer 1, André H. Gröschel 5, Axel H. E. Müller 5, Matthias Ballauff 1,2, Roland Steitz 1

1 – Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin 2 – Department of Physics, Humboldt-University Berlin

3 – Department of Physical Chemistry, Ruprecht-Karls-Universität Heidelberg 4 – Institute Laue-Langevin

5 – Macromolecular Chemistry II, University Bayreuth * - [email protected]

Planar multi stimuli responsive PDMAEMA brushes from diblock copolymer Langmuir layers with varied grafting density were prepared by Langmuir-Schäfer transfer. Utilizing neutron reflectometry, NR, the brushes were analyzed at the solid-liquid interface in the temperature range 20 to 60 °C for hydrostatic pressures from 1 to 1000 bar. A novel theoretical model of the brush density profile as a function of grafting density σ, temperature T and hydrostatic pressure p was used to fit the experimental NR data. Within that model, temperature and pressure effects are described independently. Increasing temperature caused a continuous decrease of polymer brush thickness (cf. Fig. 1). The reason for this response of the brush is a hydrophobic coil to globule transition of the polymer chains. When crossing the lower critical solution temperature (LCST) the brushes collapse into a high density polymer layer near the grafting plane and a low density Gaussian tail towards the liquid fronting phase. The new analytical model intrinsically includes the observed vertical phase separation and yields the correct position of the LCST in a thermodynamically consistent way, exclusively based on structure data. Hydrostatic pressure is found to act perfectly antagonistic to temperature. The hydrophobic collapse of the PDMAEMA brush that is caused by a temperature increase of ~10K is counterbalanced by a pressure increase of 1000 bar.

Fig. 1 Neutron reflectivity R(Q) from a PDMEAMA brush grafted to a dPS coated silicon support at a grafting density of σ = 0.22 nm-2 against D2O liquid phase as a function of sample temperature (left panel). Solid lines are fits to the experimental data according to the brush volume fraction profiles from the analytical model (right panel).


Contact Line Dynamics uring Rapid De- etting f Dilute Polymer Solutions n Hydrophobic Surfaces

Davide Biolé 1, Volfango Bertola 1*

1 – University of Liverpool, School of Engineering, Liverpool, UK * - [email protected]

The wetting dynamics of dilute polymer solutions on h ydrophobic surfaces is remarkably different from the case of simple liquids. The comparison between experiments carried out with pure water and dilute polymer solutions reveals a deep difference in the behaviour of the moving contact line during the receding phase, in the amplitude of the contact angle, as well as in the intrinsic time of the phenomenon. Recent experiments relate this behaviour to the stretching of polymer molecules caused by the receding movement of the contact line [1,2]. The present work aims to get a deeper insight of this phenomenon through systematic experiments aiming at the investigation of the independent effects of the relevant parameters (polymer concentration, Weber number, surface energy of the substrate) on the morphologies of the contact line and of the contact angle during the receding phase. In comparison with pure water, the contact line of dilute polymer solutions is pinned at several points on the impacting surface; thus, the effect of the polymer is to slow down the receding phase after drop impact, also modifying the morphology of the contact line. The results of this experimental work allow a quantitative estimation of the dissipative force opposed to the contact line displacement, shedding more light on our understanding of the wetting dynamics of dilute polymer solutions.

Fig. 1 Formation of liquid filaments and dendrites during the receding contact line motion.

Literature: 1. Smith, M.I., Bertola, V., 2010. Effect of polymer additives on the wetting of impacting

droplets. Physical Review Letters 104: 154502. 2. Bertola, V., 2013. Dynamic wetting of dilute polymer solutions: the case of impacting

droplets. Advances in Colloids and Interfaces 193-194: 1-11. Acknowledgements: This project is supported by the University of Liverpool – A*STAR (Singapore) research partnership.


Characterization of PDADMAC onolayers on ica by treaming otential asurements

Aneta Michna*, Zbigniew Adamczyk

Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Cracow, Poland


Physical properties of the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) having a molecular weight of 160 kDa were characterized. The bulk characteristics involved the diffusion coefficient (hydrodynamic diameter), and electrophoretic mobility as a function of polyelectrolyte solution concentration for various ionic strengths. The hydrodynamic diameter data suggested that the macromolecules assume an extended, wormlike shape in the bulk. Accordingly, the diffusion coefficient was interpreted in terms of a simple hydrodynamic model pertinent to flexible rods, previously applied for poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) [1]. The thorough characterization in the bulk allowed a proper interpretation of PDADMAC adsorption on mica studied by the streaming potential technique. The obtained results were quantitatively interpreted in terms of the electrokinetic model postulating a 3D adsorption of macromolecules as discrete particles. These measurements allowed one to determine the coverage of PDADMAC as a function of zeta potential of mica. Furthermore, the stability of the polyelectrolyte monolayers against prolonged washing (up to 24 h) also was determined using the streaming potential method. It was demonstrated that PDADMAC layer is resistant to washing. It also was concluded that due to high sensitivity, the electrokinetic method applied can be effectively used for quantitative studies of polyelectrolyte adsorption, desorption, and reconformation.

Literature:

1. Adamczyk Zbigniew, Zembala Maria, Warszyński Piotr, Jachimska Barbara, 2004. Characterization of Polyelectrolyte Multilayers by the Streaming Potential Method. Langmuir 20: 10517-10525

Acknowledgements:

This work was supported financially by the grant POIG 01.01.02-12-028/09-00


Non-equilibrium Morphological Transition Kinetics in Block Copolymer Micelles Observed by Millisecond Time-Resolved SAS

Reidar Lund 1*, Lutz Willner 2, Peter Lindner3 and Theyencheri Narayanan4

1 Dept. of Chemistry, University of Oslo Postboks 1033 Blindern, 0315 Oslo, Norway

2 – Jülich Centre for Neutron Science (JCNS) & Institute for Complex Systems (ICS), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany.

3 –Institute Laue Langevin (ILL), Grenoble, France. 4 – European Synchrotron Radiation Facility (ESRF) Grenoble, France.

* [email protected]

The kinetics of block copolymer micelles is still not fully understood [1]. Such processes include both equilibrium kinetics, e.g. molecular exchange, and non-equilibrium kinetics associated with morphological transitions and the formation of micelles. Earlier we have focussed on the formation kinetics where we showed that the kinetic pathway is characterised by a nucleation & growth type mechanism where unimer (single) chain exchange is the dominating fundamental elemental step [2]. Here we focus on the structural and kinetic aspects of a cylinder-to-sphere structural transition occurring in a model amphiphilic block copolymer system upon variation of the interfacial tension. We demonstrate that the transition is governed by entropic chain stretching in the core, which is more prominent at high interfacial tensions. We further show that we can directly follow these transitions in the real time by small angle scattering methods using both neutrons (TR-SANS, D11, ILL) and X-rays (TR-SAXS, ID02, ESRF) and by employing a stopped-flow apparatus for rapid mixing. The results show that the cylinders typically rapidly dissociates into spherical micelles within some few hundreds of milliseconds and thereafter reorganize to the final equilibrium spherical micelles within seconds. Interestingly, the transition seems to be driven by instabilities over the whole cylinder leading to fragmentation, which is followed by reorganization and growth of these entities into final spherical micelles. This contrasts earlier studies where the cylinders were suggested to decompose from the (more) unstable ends [3]. The opposite transition is not possible where the system rather ends up in another spherical micellar structure. We will discuss this behaviour in connection with some recent results on the respective “equilibrium” exchange kinetics that can be accessed using time resolved SANS [1]. We will try to interrelate and discuss kinetic pathways in block copolymer micelles and how this insight might be used to create cost-effective nano-particles. Literature:

1 R. Lund; L. Willner and D. Richter. Adv. Polym. Sci., In press (2013). 2 R. Lund; L. Willner; M. Monkenbusch; P. Panine; T. Narayanan; J. Colmenero and D. Richter. Phys. Rev. Lett. 102, 188301 (2009). 3 S Burke and A. Eisenberg, Langmuir, 17, 6705 (2001).


New Surface Tension Prediction of Complex Mixtures

Richard Campbell1*, Ábraham Ágnes2, Imre Varga2.

1 – Institut Laue Langevin, 6 Rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9, France 2 – Department of Chemsitry, Eötvös-Loránd University, H-1518 Budapest, Hungary


While the surface tension of complex mixtures determines the fate of important natural processes like the stability of aerosol droplets in clouds and the biological function of lung surfactants, the property is notoriously difficult to interpret and model. It was established over a decade ago that some strongly interacting polyelectrolyte/surfactant (P/S) mixtures exhibit a striking cliff edge peak in their surface tension isotherms while others merely have a plateau [1]. More recently we have systematically linked the surface tension peak of a strongly interacting P/S mixture to slow dynamic changes in its bulk phase behavior [2] and have demonstrated the non-equilibrium nature of the system [3]. Here we announce a simple new unifying approach that successfully predicts the surface tension of two synthetic (Pdadmac/SDS and PSS/DTAB) and one biologically-relevant (DNA/DTAB) mixtures. The approach is based on the non-equilibrium framework of comprehensive precipitation and importantly does not need any measurements of the surface properties of the mixtures; only knowledge of the surface tension isotherm of the pure surfactant and some bulk measurements of the mixtures are required. This simplification in our understanding of the surface properties of strongly interacting macromolecular mixtures may lead to the optimization of a broad range of applications involving commercial synthetic polymers, DNA and proteins at surfaces in areas such as targeted drug and gene delivery.

Fig. 1. Surface tension of aged Pdadmac/SDS (red) and PSS/DTAB (blue) solutions with predictions of their surface tension not based on any surface measurements of the mixtures.

Literature: 1. Taylor Diana, Thomas Robert, Penfold, J. 2007. Adv. Colloid Interfac. 132: 69–110. 2. Campbell Richard, Yanez Arteta Marianna, Angus-Smyth Anna, Nylander Tommy, Varga

Imre. 2011. J. Phys. Chem. B. 115: 15202–15213. 3. Campbell Richard, Angus-Smyth Anna, Yanez Arteta Marianna, Tonigold Katrin, Nylander

Tommy, Varga Imre. 2010. J. Phys. Chem. Letters. 1: 3021–3026.


Surface Charge Effects on the Hydration of Polyelectrolyte Multilayers under Confinement

Stephen B Abbott1*, Wiebe M de Vos2, Laura LE Mears1, Robert Barker3, Robert M Richardson1, Stuart W Prescott4.

1 School of Physics, University of Bristol, BS8 1TL, UK 2 Membrane Science and Technology, University of Twente, Netherlands

3 Institute Laue Langevin, 6 Rue Jules Horowitz, F-38042 Grenoble, France 4 School of Chemical Engineering, University of New South Wales, Australia

* [email protected]

A polyelectrolyte multilayer (PEM) is formed from alternate layer by layer deposition of cationic and anionic polymers. Potential applications of PEMs range from biomedical uses[1], to optics[2], to drug delivery[3]. For all applications the amount of hydration, and therefore the swelling of the layer, is vital to the designed effectiveness of the PEM. Using neutron reflectivity we examine how the hydration of PEM stacks with 11, 23 and 47 bi-layers responds to a mechanical compression between 0 and 5 bar with a surface force type apparatus utilising a flexible Melinex® membrane[4], fig. 1. We also consider the odd-even effect under confinement where the final layer is either the cationic polymer poly(allyl amine hydrochloride), PAH, or the anionic polymer poly(styrene sulfonic acid), PSSA.

Fig. 1: Schematic of the

compression cell.

To assist our analysis, 3 selected layers in each sample are fabricated using deuterated PSSA to split the sample into 4 equal cells. This allows us to analyse the distribution of the water within the PEM stack and to determine the role and importance of the terminating layer, the number of bi-layers and the confining pressure. In addition, we also consider a special case where we compress a PAH terminated PEM on the silicon with a PSSA terminated PEM on the Melinex® membrane, so that there is no net surface charge.

Fig. 2: Neutron reflectivity curves

and fits for a PSSA terminated sample with 47 bi-layers at 0, 3 and 5 bar. Data sets offset for clarity.

Fig. 3: Charge distribution in a

PSSA terminated sample.

Our results demonstrate that the PSSA terminated PEM stacks are more hydrated than PAH terminated stacks and that with a 5 bar confining pressure the hydration is dependent on the number of bi-layers. The hydration is also observed to be uniformly distributed in PSSA terminated samples, whereas the layers closest to the Si preferentially dehydrate for PAH terminated samples. In the case where two PEMs are compressed together, the PEM dehydrates more in the layers nearest to the contact interface. To explain our observations, we use a qualitative model whereby the surface charge of the PEM, which is determined by the final adsorbed layer, influences the charge distribution within the rest of the PEM, fig. 3. The amount of charge is then directly linked to the hydration of the PEM when confined. This model describes all the observed behaviour of PEMs under confinement.

Literature:

1. Boudou, T.; Crouzier, T.; Ren, K.; Blin, G.; Picart, C.; 2010, Adv. Mater., 22, 441–467.

2. Hiller, J.; Mendelsohn, J.D.; Rubner, M.F.; 2002, Nature Materials, 1, 59-63. 3. Shchukin, D.G.; Sukhorukov, G.B.; Möhwald, H.; 2003, Angew. Chem., Int.

Ed. 42, 4472-4475. 4. de Vos, W.M.; Mears, L.L.E.; Richardson, R.M.; Cosgrove, T; Dalgliesh,

R.M.; Prescott, S.W: 2012, Rev. Sci. Instrum., 83, 113903.


Translational Dynamics of Molecules in Synthetic and Natural Polymers as Studied by NMR

Victor Rodin 1*

1 – Department of Physics, University of Surrey, Guildford, Surrey, GU2 7XH, UK


This work is dedicated to the examination of those contemporary NMR- methods, which are used in the study of molecular translational dynamics in the systems of different level of complexity (solutions of polymers, emulsions, gels, polymer films, biopolymers and the porous heterogeneous systems of natural origin or construction materials) [1-4]. Contemporary possibilities of the methods of NMR- relaxation (spin-spin, spin-lattice and cross relaxation), NMR diffusometry (pulse field gradient NMR) and methods of double-quantum-filter (DQF) NMR in a study of diffusion properties and molecular dynamics in the systems with the anisotropic properties are considered [1, 3, 4]. The work shows how the study results in an information about molecular dimensions / form of limitations, structure of fluid medium in the heterogeneous systems, character of limitation and the structure of the surrounding matrix [1, 3]. DQF NMR is applied for investigating the systems, in which there is an order (on the macro- or the micro-levels), in particular for fibres and porous systems or the systems with anisotropic motion of molecules [1, 4]. The results obtained reveal also the special feature of the approaches of one-dimensional and two-dimensional NMR [1, 5] and show examples of the work of these methods [5] in addition to the traditional methods of single- quantum NMR-spectroscopy. The work presents the data of two-dimensional correlation NMR-spectroscopy (DD COSY) as the distributions of diffusion coefficients in two orthogonal directions on the systems with anisotropic mobility [5]. Simulations of two-dimensional NMR-experiments have been done showing how it leads to the explanation of experimental data on the anisotropy of diffusion coefficients. These NMR- methods reveal the correlation of the diffusion motion of molecules along either collinear or orthogonal directions of applied pulse gradients of magnetic field. The results on some materials with anisotropic structure demonstrated how these methods reveal microscopic local anisotropy in the presence of global isotropy.

Literature:

1. Callagan P.T., 2011,Translational Dynamics and Magnetic Resonance, Oxford University Press. 2. Cosgrove T., Rodin V. et al. 2007, J.Polymer Research, Vol.14. N3. P.175–180 3. Rodin V., McDonald P., Valori A., 2011, New Journal of Physics. 4. Rodin V. Magnetic resonance methods, 2004. Moscow: Press. MFTI. 95 pp. ISBN 5-7417-0228-7. 5. Rodin V., McDonald P., Zamani S. 2013, Diffusion Fundamentals.


Temperature-induced Phase Transition in Aqueous Polymer Solutions and Gels Studied by NMR and Other Methods

Jiří Spěváček1*, Rafal Konefal1, Julie Šťastná2, Lenka Hanyková2, Helena Valentová2

1 – Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovský Sq. 2, 162 06 Prague 6, Czech Republic

2 – Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 180 00 Prague 8, Czech Republic


It is well known that thermoresponsive polymers show in aqueous solutions a lower critical solution temperature (LCST). They are soluble at lower temperatures but heating above the LCST results in phase separation. For dilute solutions a coil-globule transition was revealed by light scattering at the LCST while for semidilute and concentrated solutions aggregation results in formation of larger globular-like structures called mesoglobules. When these polymers are chemically crosslinked their hydrogels undergo around this temperature a volume phase transition (collapse). Their thermosensitivity makes thermoresponsive polymers interesting for miscellaneous biomedical and technological applications. Of various methods, NMR spectroscopy was also used in investigations of these systems1. Three types of thermoresponsive polymer systems studied by us recently will be discussed here:

(i) From comparison of the values of the enthalpy change H based on data obtained by 1H NMR spectroscopy with H values obtained by DSC we confirmed for D2O solutions of several thermoresponsive homopolymers (poly(N-isopropylmethacrylamide) (PNIPMAm), poly(vinyl methyl ether), poly(N-vinylcaprolactam)) in broad range of concentrations that cooperative unit is the whole macromolecule and that also in semidilute and concentrated solutions their chains undergo coil-globule transition during phase separation.

(ii) Using 1H NMR spectroscopy we studied temperature-induced phase transition in D2O solutions of diblock and triblock copolymers poly(ethylene glycol) (PEG)-poly(N-isopropylacrylamide) (PNIPAm) of the AB and A(B)2 type, respectively. We have found that presence of the PEG block significantly affects phase transition and globular structures of PNIPAm component, as well as behaviour of water molecules.

(iii) Combination of NMR, DSC and dynamic mechanical measurements was used to study collapse phase transition in hydrogels of interpenetrating networks (IPN) PNIPAm/ PNIPMAm. A single transition at temperatures between transition temperatures of neat components was revealed in most IPN samples by NMR and DSC, indicating enhanced mutual intertwining of PNIPAm and PNIPMAm chains. In all samples the collapse transition results in substantial increase of both components of the shear modulus.

Literature:

1. Spěváček Jiří, 2009, NMR investigations of phase transition in aqueous polymer solutions and gels, Curr. Opin. Colloid Interface Sci. 14, 184-191.

Acknowledgments:

Support by the Czech Science Foundation (project 13-23392S) is gratefully acknowledged.


Effect of PEM Coated PDMS on Freshwater Biofouling

Johannes Frueh 1*, Meiyu Gai1, Qiang He1

1 Key Laboratory of Microsystems and Microstructures Manufacturing, Ministry of Education, Micro/Nano Technology Research Centre, Harbin Institute of Technology, Yikuang Street 2,

Harbin 150080, China * [email protected]

Biofouling is one of the biggest problems of water-borne systems.1 Since not only marine but also freshwater-based structures are affected,2 the results of a study of biofouling in this environment are presented in the poster. The focus of the study are the antifouling properties of polyelectrolyte multilayers (PEM)3 compared with currently used silicon rubber (PDMS)4 based fouling release coatings. The poster contains the results of a systematical screening of the mechanical, surface charge and surface nano- heterogeneous properties of the investigated PEM and PDMS systems. It can be shown that negatively charged non crosslinked and crosslinked PEM coated PDMS succeds the antifouling properties of purely PDMS based fouling release coatings. The PEM films are not only able to reduce the biofouling, but are additionally able to control the type of settled bacteria (gram positive or negative). The negative terminated surfaces inhibit the settlement of gram positive bacteria, probably due to repulsion of negatively charges, whereby the positive terminated surfaces inhibit the settlement of gram negative bacteria, due to the liquification of the bacteria cell wall5 due to interaction of positively charged hydrophobic PEM and the cell wall5.

Literature:

1. Railcin A I, 2000, Marine biofouling (Florida: CRC Press) 2. Li Z, 1997, Maintenance of inland waterways and aids to navigation in China Reform in inland water transport: China’s experience (Hohai: United Nations) pp 109–35 3. Decher G and Schlenoff J, 2012, Multilayer Thin Films: Sequential Assembly of Nanocomposite Materials, ed G Decher and J Schlenoff (Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA) 4. http://www.sharklet.com/ accessed 2012 homepage of Sharklet company 5. Haldar J, An D, Alvarez L, Cienfuegos D, Chen J and Klibanov A M 2006 Polymeric coatings that inactivate both influenza virus and pathogenic bacteria PNAS 103 17667–71

Fig. 1: Biofouled surfaces after 21 days a) negatively charged PEM, b) PDMS reference sample

Acknowledgements:

This work was supported by the National Nature Science Foundation of China (91027045), 100-talent Program of HIT, China Postdoctoral Science Foundation (2013M531019) and New Century Excellent Talent Program (NCET-11-0800), Harbin Institute of Technology.


Behaviour of Thermo-sensitive Copolymer Microgels at the Oil/Water Interface

Yaodong Wu1, Susanne Wiese2, Andreea Balaceanu1, Walter Richtering2, Andrij Pich1*,

1 –Functional and Interactive Polymers, Institute of Technical and Macromolecular Chemistry, DWI RWTH Aachen University, Forckenbeckstr. 50, 52056 Aachen, Germany

2 –Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52056 Aachen, Germany


Microgels are soft particles consisting of physically or chemically cross-linked polymer network. A novel application of microgels has been developed recently, in which they are employed in the formation of particle-stabilized emulsions, similar to Pickering emulsion.1 However, microgels have the behavior that falls between hard spheres and ultra-soft systems.2 The assembly laws deduced from the interfacial behavior of hard particles at the oil/water interface seem to be not completely suitable for microgels, since soft microgel particles are highly deformed at the oil/water interface.3

Herein, copolymer microgels based on N-vinylcaprolactam (VCL) and two acrylamides, N-isopropylacrylamide (NIPAm) and N-isopropylmethacrylamide (NIPMAm), with various copolymer compositions were synthesized, and investigated in the aspect of interfacial tension. A statistical distribution of the monomer units in the both microgel networks4 gives a straightforward possibility to study systematically the influence of the chemical structure on the interfacial behavior of microgels. The equilibrium interfacial tension and the time for reaching the equilibrium status, which can be considered as thermodynamic aspect and kinetic aspect, respectively, vary with temperature and chemical compositions of microgels. It is also indicated that the chemical environment itself, rather than through microgel size has a governing influence on the interfacial behaviour of microgels at the toluene/water interface.

Scheme 1. The adsorption of microgels below and above VPTT.

Literature:

1. Brugger, B.; Rosen, B. A.; Richtering, W. 2008. Langmuir 24: 12202-12208. 2. Eckert, T.; Richtering, W. 2008. Journal of Chemical Physics 129: 124902-1-5. 3. Geisel, K.; Isa, L.; Richtering, W. 2012. Langmuir 28: 15770-15776. 4. Balaceanu, A.; Mayorga, V.; Lin, W.; Schürings, M.-P.; Demco, D.; Böker, A.; Winnik, M.;

Pich, A. 2013. Colloid & Polymer Science 291: 12-31.


Adsorption f Short Block Copolymers n Solid Surfaces. A Monte Carlo Study

W. Rzysko and P. Bryk

Department for the Modeling of Physico-Chemical Processes Maria Curie-Sklodowska University, 20-031 Lublin, Poland


Adsorption of diblock copolymers on flat surfaces is studied using lattice Monte Carlo simulations. The model consists of fully flexible diblock copolymer adsorbed on a square lattice. We determine full topology of the phase diagrams for a series of symmetric copolymer models starting from chain lengths M=4 up to 16. For the shortest chains the order-disorder phase transition is of the first order while for the longer chains we find a critical end-point. The chemical potential and density for the gas-disordered liquid increases non-monotonically, whereas the critical temperature increases monotonically with chain length. We also determine Minkowski measures in order to better characterize the structure of the adsorbed phases.

Fig. 1 Snapshot for an ordered phase of the adsorbed diblock copolymer. Chain length M=8.

Acknowledgements:

Support from 7th EU Framework Program PIRSES-GA-2010-268498 entitled „Statistical Thermodynamics and Computer Simulations of Complex Molecules in Bulk and at Surfaces” is gratefully acknowledged.


A Density Functional Study of End-Grafted Chain Layers:

Temperature Effects

Małgorzata Borówko, Stefan Sokołowski, Tomasz Staszewski*

Maria Curie-Skłodowska University Department for the Modelling of Physico-Chemical Processes


The properties of end-grafted chain layers have been intensively studied in recent years. These systems are important for numerous technological processes, including stabilization of colloidal suspensions, chromatographic separation, lubrication, adhesion, drug delivery and production of protective coatings. The structure of the chain interphase result from a complex interplay between entropic and enthalpic effects in the system. A lot of theoretical approaches have been applied to describe polymer-tethered surfaces. One of them is the density functional theory proposed by Yu and Wu [1] and extended in our previous papers [2-4].

In this work we present the density functional study of the structure of end-grafted chain layers immersed into explicit solvents. We introduce the following model. The chains are freely jointed tangent spheres. The grafted chains are inert with respect to the substrate. The fluid molecules interact with the solid surface via Lennard-Jones (9-3) potential. All segments interact via Lennard-Jones (12-6) potential. We have calculated the density profiles of all components and the thickness of the brush. The calculations have been carried out for selected model systems.

First, we investigate an influence of temperature on the structure of the grafted chain layer. We study the brushes in solvents with different affinities to the grafted chains. We discuss how the fluid density, grafting density and fluid-brush interactions affect the brush thickness at selected temperatures. We consider the brush thickness as a function of temperature. It is shown that a shape of such a function depends on the fluid density. For low fluid densities the brush height monotonically increases with increasing temperature. On contrary, at high fluid densities the brush thickness decreases. We show that at a certain fluid density the brush height is almost independent of temperature. Moreover, it is shown that an increase of fluid density causes an increase or a decrease of the brush height depending on temperature.

Second, we calculate the force acting on a selected segment of a tethered chain that leads to pulling the chain off the wall. The effects due the presence of other chains and fluid molecules, as well as temperature, are considered.

Literature:

1. Y. X. Yu, J. J. Wu, J. Chem. Phys., 117 (2002) 2368. 2. M. Borówko, S. Sokołowski, T. Staszewski, J. Phys. Chem B, 113 (2009) 4763. 3. M. Borówko, S. Sokołowski, T. Staszewski, J. Colloid and Interface Sci., 356 (2011) 267. 4. M. Borówko, S. Sokołowski, T. Staszewski, J. Phys. Chem. B, 116 (2012) 3115.


Non-equilibrium ature of wo-dimensional sotropic and ematic oexistence in myloid ibrils at iquid nterfaces

Sophia Jordens 1, Lucio Isa 2, Ivan Usov 1, Raffaele Mezzenga 1*

1 – ETH Zurich, Laboratory of Food & Soft Materials, Schmelzbergstrasse 9, 8092 Zurich, Switzerland

2 – ETH Zurich, Laboratory for Surface Science & Technology, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland


Two-dimensional alignment of shape-anisotropic colloids is ubiquitous in nature, ranging from interfacial virus assembly to amyloid plaque formation. The principles governing two-dimensional self-assembly have therefore long been studied, both theoretically and experimentally, leading, however, to diverging fundamental interpretations on the nature of the two-dimensional isotropic–nematic phase transition. Here we employ single-molecule atomic force microscopy, freeze-fracture shadow-casting cryogenic scanning electron microscopy and passive probe particle tracking to study the adsorption and liquid crystalline ordering of semiflexible β-lactoglobulin fibrils at liquid interfaces. Fibrillar rigidity changes on increasing interfacial density, with a maximum caused by alignment and a subsequent decrease stemming from crowding and domain bending. Coexistence of nematic and isotropic regions is resolved and quantified by a length scale-dependent order parameter S2D(d). The nematic surface fraction increases with interfacial fibril density, but depends, for a fixed interfacial density, on the initial bulk concentration, ascribing the observed two-dimensional isotropic–nematic coexistence to non-equilibrium phenomena.

Fig. 1 Atomic Force Microscopy image of semiflexible β-lactoglobulin amyloid fibrils that have aligned into two-dimensional liquid crystalline domains by passive adsorption to an air-water interface.

Literature:

Sophia Jordens1, Lucio Isa2, Ivan Usov1, Raffaele Mezzenga1. 2013. Non-equilibrium nature of two-dimensional isotropic and nematic coexistence in amyloid fibrils at liquid interfaces. Nature Communications. doi:10.1038/ncomms2911


The Synergism between Hydrophobically Modified Inulin and Cationic Surfactant

Jordi Morros1, María Rosa Infante1, Maria da Graça Miguel2, Björn Lindman2, Ramon Pons1*

1 – Institut de Química Avançada de Catalunya (IQAC-CSIC),Barcelona, Spain. 2 – Departamento de Química da FCTUC, Coimbra, Portugal.


As petroleum feedstock decreases, the development of new renewable bio-based and efficient chemicals has attracted more and more interest. Recently, a natural polydisperse polysaccharide named inulin has gained considerable attention. This polysaccharide extracted from chicory roots consists mainly of ß(2-1)-fructosyl furanose units, and has unique properties due to its linear structure and its rather low molecular weight range in comparison to other polysaccharides such as cellulose and starch.

This relatively small polymer has focused special interest when several hydrophobic chains are attached on its backbone [1]. This hydrophobically modified inulin (HMI) is able to stabilize many dipersed systems such as o/w emulsions, solid dispersions or films by steric stabilization mechanisms [1]. Additionally, it possesses other important properties like surface activity comparable to those of molecular surfactants or thermo-reversible associative behaviour in aqueous solutions. Also, the hydrophobic groups grafted onto the polyfructose backbone tend to aggregate in order to limit their contact with the solvent leading to the formation of stable core-shell soft nanoparticles [2].

In the present work, we explore the interaction of these macromolecular structures with a well-known vesicle forming cationic surfactant, didodecyldimethylammonium bromide (DDAB). Initially, one could expect that HMI would stabilize vesicles by the already described steric stabilization mechanisms, but surprisingly this is not the case. Helped by characterization techniques, we have elucidated the nature of these polymer-surfactant interactions by proposing interaction models for surface tension, zero-shear viscosity and SAXS profiles. Here, we present our results with several synthesized HMIs [3] together with pristine inulin (without hydrophobic modifications) and Inutec®SP1 (commercial HMI) for comparative reasons, and we propose some possible applications for these interesting mixed micelles formed by DDAB and HMI.

Literature:

[1] Th.F Tadros, A Vandamme, B Levecke, K Booten, C.V Stevens, 2004, Stabilization of emulsions using hydrophobically modified inulin, Adv. Colloid Interface Sci., 108, 207-226. [2] J. Morros, MR. Infante, R. Pons, 2012, Surface activity and aggregation of pristine and hydrophobically modified inulin, Soft Matter, 8, 11353-11362. [3] J. Morros, B. Levecke, MR. Infante, 2010, Synthesis of β-hydroxyalkyl ethers of inulin in aqueous surfactant media, Carbohydrate polymers, 82, 1168-1173. Acknowledgements: This research was financially supported by a Bilateral Project (P2007PT0050), a COST project (COST-STSM-D36-05462), Mineco (CTQ2010-14897 and MAT2012-38047-C02-02) and Generalitat de Catalunya (CTQ2009-SGR1331). Technical support provided by J. Caelles and I. Carrera for SAXS measurements and Surface Tension measurements, respectively, is especially acknowledged. And thank you for the selflessly material support of Beneo BBC in this research.


Effect of Different Parameters ver the Dispersion Stability of Silica Qaisar Abbas Bhatti1*, Musa Kaleem Baloch1, Simona Schwarz2, Gudrun Petzold2

1Department of chemistry Gomal University Dera Ismail Khan, Pakistan

2Leibniz-Institut für Polymerforschung Dresden e.V., Deutschland * - [email protected]

Silica dispersion has a number of applications in our daily life and needs detail investigation to establish the effect of various parameters over the size, size distribution and its stability. Therefore, the silica was dispersed and the size and size distribution and surface charge have been investigated as a function of ultrasonication time, added polymer (Polyvinylpyrrolidone) concentration and molecular mass. It has been concluded that though the size distribution remains almost unaffected by the ultrasonication time but the surface charge was increased with the increase in ultrasonication time up to 20 minutes and then it leveled off. Further the polymers added were adsorbed over the surface of the particles and increased the surface charge (Zeta potential) and the increase proportional to the molecular mass of the polymer. Due to the reason the added polymers introduced the steric as well as electrostatic stabilization and the dispersions became stable. However, if the particles were not properly dispersed before the addition of polymer then the available agglomerates did not break by ultrasonication and hence the distribution of the particles size was widened.

Keywords: Silica dispersion; Zeta potential; Poly (vinylpyrrolidone); pH; ultrasonication; stability of dispersion.

References. 1 Petzold G,Schwarz S (2006) Interactions between Polyelectrolytes and Inorganic particles. In: Encyclopedia of Surface and Colloid Science, 2nd edn. Taylor & Francis, New York 2 Pattanaik M, Bhaumik SK., Adsorption behaviour of polyvinyl pyrrolidone on oxide surfaces” (2000) Materials’ letters. 44:352-360 3 Bhatti QA, Schwarz S, Petzold G., Stability for dispersions.Determining the effects of PVP on the sedimentation of clay suspensions. (2010) European Coatings journal. 08:33-37 4 Lerche , D. Dispersion stability and particle characterization by sedimentation kinetics in a centrifugal field . J.Dispers. Sci. Technol. 2002 , 23 , 699 – 709 5 Kuz’kina IF, Ivankova II, Zubov VP, Schauer T, Entenmann M, Elsenbach CD (2000) European coatings journal .12:18-23. 6 Zubov VP, Serebryakova NA, Arutyunov IA, Bulychev NA, Kuz’kina IF, Khrustalev YA, Influence of mechanical activation on the surface of inorganic pigment stability of aqueous dispersions in the presence of etilgidroksietilitsellyuzycrystal. Volloid Journal . 3 (66), 343-351 New (2004)

Acknowledgements:

This research project has been supported by budgetary funds of the Higher Education Commission of Pakistan(under the International Research support Initiative Programme). One of the Authers1*, acknowledges Leibniz-Institut für Polymerforschung (Dresden-Germany) for providing the lab facilities and Ms Sandra Schütze for her skilful work.


Interfacial Layers from the Protein HFBII Hydrophobin: Dynamic Surface Tension, Dilatational Elasticity and Relaxation

Times

Nikola A. Alexandrov1*, Krastanka G. Marinova1, Theodor D. Gurkov1, Krassimir D. Danov1, Peter A. Kralchevsky1, Simeon D. Stoyanov2,3, Theodorus B. J. Blijdenstein2, Luben N.

Arnaudov2, Eddie G. Pelan2, Alex Lips4

1 – Department of Chemical Engineering, Faculty of Chemistry, Sofia University, 1164 Bulgaria 2 – Unilever Research & Development Vlaardingen, 3133AT Vlaardingen, The Netherlands

3 – Laboratory of Physical Chemistry and Colloid Science, Wageningen University, 6703 HB Wageningen, The Netherlands

4 – Unilever Research & Development, Port Sunlight, Wirral, Merseyside CH63 3JW, UK1 * - [email protected]

The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is detected as an increase in the error of the fit of the pendant-drop profile by means of the Laplace equation of capillarity. The relaxation of surface tension after interfacial expansion follows an exponential-decay law, which indicates a barrier mechanism of adsorption. The experimental data for the relaxation time suggest that the adsorption rate is determined by the balance of two opposing factors: (i) the barrier to detachment of protein molecules from bulk aggregates and (ii) the attraction of the detached molecules by the adsorption layer due to the hydrophobic surface force. The hydrophobic attraction can explain why a greater surface coverage leads to a faster adsorption. The relaxation of surface tension after interfacial compression follows a different, square-root law. Such behavior can be attributed to surface diffusion of adsorbed protein molecules that are condensing at the periphery of interfacial protein aggregates.

The surface dilatational elasticity, E, is determined in experiments on quick expansion or compression of the interfacial protein layers. At lower surface pressures (< 11 mN/m) the experiments on expansion, compression and oscillations give close values of E that are increasing with the rise of surface pressure. At higher surface pressures, E exhibits the opposite tendency and the data are scattered. The latter behavior can be explained with a two-dimensional condensation of adsorbed protein molecules at higher surface pressures. The results could be important for the understanding and control of dynamic processes in foams and emulsions stabilized by hydrophobins, as well as for the modification of solid surfaces by the adsorption of such proteins.


Structural Investigation of Aqueous Systems of Nonionic Polysaccharide Levan by SAXS, SLS and DLS

Elizabeta Benigar,1 Iztok Dogša,2 David Stopar,2 Andrej Jamnik,1 Matija Tomšič.1*

1 Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva cesta 5, 1000 Ljubljana, Slovenia

2 Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia * - [email protected]

Non-ionic polysaccharide Levan exhibits rather peculiar non-gelling behavior in pure aqueous systems up to high polymer concentrations (60 wt. %) [1]. On the other hand only up to 8 wt. % of this polysaccharide in some bacterial biofilms already forms a weak hydrogel (e.g. biofilms of Bacillus subtilis subsp. Subtilis str. NCIB 3610, where Levan was found as the major polymeric component). Our long-term goal is to explore these differences in behavior of polysaccharide Levan isolated from biofilm of Bacillus subtilis in various aqueous systems from the structural point of view in order to recognize and address the possible causes for such discrepancies. On the first stage the structural features of pure aqueous systems of polysaccharide Levan of the bacteria Bacillus subtilis, Zymomonas mobilis, and Erwinia herbicola were investigated by the small angle x-ray scattering method (SAXS) utilizing the data evaluation based on the string-of-beads model [2]. This model has already been proven to be useful for such type of structural investigations yielding the detailed information about the values of molecular parameters such as molecular flexibility, persistence and correlation lengths on different length-scales, and information on effective interparticle interactions. Basic information on the size of polymer molecules in the system that is needed to set up such model can be obtained utilizing the static light scattering (SLS) technique. Similarly the dynamic light scattering (DLS) method can provide complementary dynamic and structural results.

Fig. 1. Monomer units of polymer are approximated by spheres that are connected into a string in the string-of-beads model. Adapted from ref. [2].

[1] Arvidson, Sara A., Rinehart B. Todd, Gadala-Maria Francis, 2006. Concentration regimes of

solutions of levan polysaccharide from Bacillus sp.. Carb. Polymer 65: 144–149. [2] Dogsa Iztok, Štrancar Janez, Laggner Peter, Stopar David, 2008. Efficient modeling of

polysaccharide conformations based on Small-Angle X-ray Scattering experimental data. Polymer 49: 1398-1406.


Calcium ediated olyelectrolyte dsorption on ike-charged urfaces: tabilization ffects in anoplatelet uspensions

Martin Turesson1*, André Nonat2 and Christophe Labbez1

1 ICB, UMR 6303 CNRS, Université de Bourgogne, Dijon Cedex, F-21078, France * - [email protected]

One of the most widespread example of a polymerically stabilized colloidal system is fresh cement paste. In this context, anionic comb polymers with a charged backbone (mostly polycarboxylate esters) adsorb on the highly negatively charged cement nanoplatelets (calcium silicate hydrate) at conditions of high pH and high calcium concentration. Grafted to the backbones are hydrophilic side chains (PEG) which are thought to provide the required entropy (steric hindrance) to overcome ion correlation forces which otherwise cause the cement to aggregate1. The result is a high performance concrete with enhanced workability, durability and mechanical properties. In this contribution, our aim is to rationalize the mechanisms of the polymer adsorption and the resulting stabilization.

By means of Monte Carlo simulations at the level of the primitive model, the polymer model parameters and the ion-pairing between calcium ions and charged monomers were determined by fitting experimental titration data2,3 of polyacrylic acid in various salt solutions. The adsorption behavior of model polyelectrolytes (linear and branched) in contact with like-charged surfaces and divalent counterions, was then studied as a function of the calcium and polymer concentration. Under similar conditions, a model dispersion of many negatively charged platelets, was studied in the presence of three different types of anionic polyions. For this purpose, molecular dynamics simulations were empl

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