This content has been downloaded from IOPscience. Please scroll down to see the full text.

Download details:

IP Address: 54.39.106.173

This content was downloaded on 11/10/2020 at 22:00

Please note that terms and conditions apply.

You may also be interested in:

Flexible Electronics, Volume 2: Single-crystal Si TFT

V K Khanna

Basic Surfaces and their Analysis: Thermodynamics of surfaces: equilibrium crystal shape

L V Goncharova

Open-Channel Microfluidics: Capillarity theoretical basis

J Berthier, A B Theberge and E Berthier

Discussion of the surface tension of liquid helium

R M Bowley

Critical Review of Removal of Nano Materials in Waste Streams

Solomon W. Leung, Bradley Williams, Karl De Jesus et al.

Dependences of spin polarization on the control parameters in the spin-polarized injection through

the magnetic p-n junction

Zhang Lei, Deng Ning, Ren Min et al.

Effect of F-Doping on Optical and Thermal Properties of Soda Magnesium Silicate Glasses for

Ultralow-Loss Fibers

Shin-ichi Todoroki and Shigeki Sakaguchi

The calibration of a Meson Spectrometer with a Least Squares Minimization technique

M H Shah Bukhari

IOP Concise Physics

NanomaterialsThe original product of nanotechnology

Maria Benelmekki

Chapter 1

Introduction

The impact of surface energy on the behavior of nanostructures and nanomaterials(NMs) is more significant due to the huge surface area involved in nanosizedmaterials. This chapter discusses in a very concise way the methods of synthesis ofNMs, the origins of the surface energy in NMs, and a few mechanisms for NMs toreduce their surface energy. The theories of surface energy and mechanisms ofstability are also included. In addition, the chapter gives an insight into the mostcommon practices for the stabilization of nanoparticles (NPs) to avoid theirirreversible agglomeration. A good understanding of these fundamentals will leadto controlled fabrication and processing of NMs, and to a safe and responsiblemanipulation of NMs and products containing NMs either during the product-life,or at the product-end-of-life.

1.1 Introduction to nanomaterials and nanostructuresNanotechnology is the technology of design, fabrication, manipulation, andapplications of small structures (nanostructures) or small-sized materials (NMs).The typical dimension of NMs and nanostructures varies from sub-nanometer toseveral hundred nanometers. (A nanometer is 10−9 of a meter.)

The concept of nanotechnology was introduced by Richard P Feynman in 1959 [1].Since then, there have been many revolutionary developments in physics, chemistryand biology that created new fields of research, specifically in the interfaces betweenthe different scientific disciplines, resulting in a fascinating scientific and technologicmultidisciplinary progress. In 1974, Norrio Taniguchi invented the term ‘nano-technology’ and introduced the ‘top–bottom approach’ by predicting improvementsand miniaturization in integrated circuits, optoelectronic devices, mechanical devices,and computer memory devices. Approximately 10 years later, Drexler introduced the‘bottom-up approach’ when he discussed the creation of larger objects from theiratomic and molecular components as the future of nanotechnology [2].

doi:10.1088/2053-2571/ab126dch1 1-1 ª Morgan & Claypool Publishers 2019

Currently, the growing interest in nanotechnology is driven by the continuousshrinking of devices in the semiconductor industry, on one hand, and by theconsiderable progress in characterization and manipulation techniques at thenanometer scale, on the other. In fact, the further decrease in device dimensionshas followed the well-known Moore’s law (1965), where the transistor dimensionswere predicted to decrease by a factor two every year since 1950, falling well in thenanometer range and Moore’s prediction came true. In fact, the complexity of a chipcontinued to double yearly, long after 1975. The rate of doubling has only recentlyslowed to about every 18 months. Many researchers believe that devices which useelectronic nanotechnology and molecular electronics will keep Moore’s Lawaccurate into the future [3–6].

Nowadays, nanotechnologies are not only a simple continuation of miniatur-ization from micron-meter scale down to nano-meter scale, as described by NorrioTaniguchi in 1974. They involve the creation, manipulation and control of NMs andnanostructures, either by scaling up from single groups of atoms or by refining orreducing bulk materials.

1.2 Top-down and bottom-up approachesDifferent methods of production are used to optimize specific properties of NMs, theyield, and the suitability for scaling up. Methods of NM production can be dividedinto top-down, and bottom-up methods. Other emerging and promising lithographicprocedures, such as e-beam and ion-beam nanolithography and scanning-probe-based lithography, are considered of high interest in the lab because of the excellentcontrol afforded at the sub-100 nm scale. However, these procedures are notpractical for large-scale production due to their high costs and low yields.Nanoprinting can also be used for printing nanostructures and has the potentialto lower the cost considerably compared to other nanofabrication methods [1, 2, 7].

Top-down methods

Mechanical grinding methods are able to produce NPs and powders at relatively lowcost from a variety of materials using several milling techniques. This approach isoften applied in the production of metallic and ceramic NPs, but can also be used toproduce complex NPs such as bismuth-telluride-based alloys [8]. Milling involvesthermal stress and is energy intensive. Purely mechanical milling can be accom-panied by reactive milling in which a chemical or chemo-physical reaction isproduced during the milling process. However, the powders obtained show broadparticle-size distribution, significant aggregation, and impurities from the millingagent. Figure 1.1 gives a general view of the top-down synthesis of NMs, and showsboth the advantages and disadvantages of these methods.

Physical or chemical exfoliation methods also fall within the top-down categoryand are often used to obtain laminar NMs such as nanosheets and nanoflakes. Inthis field, the wide variety of chemical exfoliation methods proposed for thepreparation of graphene dispersions should be mentioned. Most are based on theso-called Hummers procedure [9].

Nanomaterials

1-2

Bottom-up methods

Bottom-up syntheses are used to produce complex nanostructured materials fromatoms and molecules, and can often be tailored to control both the chemical andphysical properties of the resulting nanostructures. These methods include gas-phaseor vapor-phase (e.g. physical vapor deposition, (PVD) and chemical vapor deposi-tion (CVD)), and liquid-phase reactions (e.g. sol–gel, Langmuir–Blodgett, thermaldecomposition, and electrodeposition among others). The liquid and gas phasesyntheses have different time scales; the slower liquid-phase processes can be used toobtain thermodynamically controlled products, while for vapor-phase synthesis,kinetic control is often the only option available. Vapor-phase production includesmethods that operate at atmospheric pressure and those that operate at low pressure[10].

Vapor deposition describes any process in which vapor is generated andcondensed on the surface of a solid, resulting in the formation of materials withat least one dimension falling in the nanometer scale. The deposition is normallycarried out in a vacuum chamber to enable control of the chemical composition. Ifthe vapor is created by physical means without a chemical reaction, the process isclassified as PVD; if the material deposited is the product of a chemical reaction, theprocess is classified as CVD. Many variations of these basic vapor depositionmethods have been developed in efforts to balance advantages and disadvantages ofvarious strategies based on the requirements of purity, structural quality, rate ofgrowth, and scaling-up, among other factors. Figure 1.2 includes examples of eachapproach, which will be addressed concisely in chapters 3–5.

The most common methods for NM synthesis based on wet chemistry are sol–gel,precipitation, thermal decomposition, self-assembly, and electrodeposition. Other

Figure 1.1. Overview on top-down methods for the synthesis of NMs.

Nanomaterials

1-3

methods such as electroless plating and templating are used to produce nano-structured materials, such as porous materials and nanotube arrays, among others.More details will be given in chapters 4 and 5.

Figure 1.3 illustrates an example of using bottom-up and top-down methods toproduce hybrid graphene-NPs material. The figure shows the extent of each methodand the different possible nanostructures obtained from each technique [11].

Many technologies have been explored to fabricate nanostructures and NMs. Forexample Cao and Wang in their book [3] suggested to group these technicalapproaches based either on the morphology of the product (figure 1.4 showsexamples of NMs with different morphologies), or on the synthesis media.According to this latest, the methods of synthesis of NMs can be categorized asfollows:

• Vapor phase synthesis, including laser reaction pyrolysis for NP synthesis andatomic layer deposition (ALD) for thin film deposition.

• Liquid phase growth, including colloidal processing for the formation of NPsand self-assembly of monolayers.

• Solid phase formation, including phase segregation to make metallic particlesin glass matrix and two-photon-induced polymerization for the fabrication ofthree-dimensional photonic crystals.

• Hybrid growth, including vapor-liquid-solid (VLS) growth of nanowires.

The emphasis within this book is on bottom-up methods. These methods aregrouped as vapor-phase and liquid-phase syntheses. Examples of the most commontechniques within these two groups will be discussed in chapters 3–5.

1.3 Overview on physical chemistry of solid surfaces1.3.1 Introduction

The ratio of surface atoms to interior atoms changes dramatically if one successivelydivides a macroscopic object into smaller parts. This is the case for NMs, whichpossess a large fraction of surface atoms per unit volume, resulting in huge changesin their physico-chemical properties. Examples of the known origins that cause these

Figure 1.2. Examples of the most common bottom-up methods for the synthesis of NMs.

Nanomaterials

1-4

changes are: (i) large fraction of surface atoms; (ii) large surface energy; (iii) spatialconfinement; (iv) reduced imperfections (small enough to be defect-free, thus showingideal strength and ballistic movement of electrons).

• What fraction of atoms is on the surface of a spherical NP?

If we consider a spherical NP of 2r diameter, with one surface atom layer of about0.2 nm of thickness ‘t’, as illustrated in figure 1.5(a). The volume of surface atomsVsurface can be estimated as 4πr2t, and the volume of the whole sphere Vsphere is 4πr

3/3.The fraction of surface atoms is given by the ratio of Vsurface to Vsphere, giving anapproximate value of ∝V V t r/ /surface sphere , [16]. Considering spheres with differentdiameters, the fraction of surface atoms increases a factor ∼109 from a macro sphereof 2 m in diameter to a nano sphere of 2 nm in diameter.

• What does the size of the surface area depend on?

Considering a cube of 9 cm each side, as shown in figure 1.5(b). The total surfacearea of the cube is SAT = 6 × 92 (486 cm2). When the cube is divided into smallercubes of 3 cm each side, the surface area SAi of each cube is 54 cm2, and the numberof small cubes filling the total volume is 27, resulting in a total surface area SAT of

Figure 1.3. Schematic presentation of methods used for the formation of graphene-NP hybrids. Adapted from[11] under CC BY 4.0.

Nanomaterials

1-5

Figure 1.4. (a) HRTEM of FeAg@Si multicore@shell NP [12]. (b) HRTEM of two CuAg mixed NPs. Bothare produced by inert gas condensation method [7]. (c) Cross-sectional (HAADF)-(STEM) image of a SrTiO3

(STO) thin film epitaxially grown on silicon substrate by MBE. (d) Enlarged view of the interface showing theepitaxial relationship between STO film and silicon substrate. Adapted from [13] under CC BY. (e) Crosssection HRTEM image of BTO (BaTiO3), LSMO (La,Sr)MnO3 and SRO (SrRuO3) layers (marked by ‘1’, ‘2’and ‘3’). (f) Cross section HAADF-STEM image of LSMO–SRO superlattices with BTO interlayers (the linesindicate the interfaces), prepared by PLD method. Adapted from [14] under CC BY 3.0. (g) TEM image of asingle CuS nanowire. (h) TEM image of CuO nanotube, prepared by electrodeposition method using anodicaluminum oxide (AAO). Adapted from [15] under CC BY 2.0.

Figure 1.5. Schemes illustrating (a) a sphere of radius ‘r’ and (b) a cube of 9 cm each size being divided insmaller cubes (see text for details).

Nanomaterials

1-6

54 × 27 = 1458 cm2. If the original cube is divided into smaller cubes of 3 nm each side,the total surface area SAT will increase to reach a value as huge as 1458 × 107 cm2.

The total surface energy increases with the overall surface area, which is stronglydependent on the dimension of material. Due to the huge surface area, all NMspossess a huge surface energy and, thus, are thermodynamically unstable ormetastable. For example, it was demonstrated that the specific surface area andtotal surface energy of 1 g of sodium chloride vary with particle size [3], the surfaceenergy increases from 7.5 × 10−5 J g−1 for a particle size of 0.77 cm to 170 J g−1 forparticle size of 10−7 cm (1 nm). This enormous surface energy is one of the mostchallenging aspects in fabrication and manipulation of NMs. Researchers andengineers continue to work on optimum methods and techniques to overcome thesurface energy, and to stabilize the nanostructures and NMs preventing their growthin size, driven by the reduction of overall surface energy.

1.3.2 Surface energy

To produce stable and controlled nanostructures and NMs, it is indispensable tohave a good understanding of surface energy and physical-chemistry of solidsurfaces. In this section, an overview on the origin of the surface energy is presented.Examples of possible mechanisms for a system or material to reduce the overallsurface energy are discussed.

If we cut a cubic solid material into two pieces, the atoms of the newly createdsurface possess fewer nearest neighbors or coordination numbers, and thus havedangling or unsatisfied bonds. Due to the dangling bonds on the surface, the atomsor molecules of the new surfaces are under an inwardly directed force (as illustratedby the red arrows in figure 1.6(b) and (c)), and thus the bond distance betweensurface-atoms and the sub-surface atoms becomes smaller. An extra force or energy(illustrated by the blue arrows in figure 1.6(b) and (c)) is required to pull the surface-atoms to their original positions.

When solid particles are very small, the decrease in bond length between thesurface-atoms and interior atoms becomes significant and the lattice constants of theentire solid particles show an appreciable reduction. The extra energy possessed bythe surface atoms is described as surface energy, surface free energy, or surfacetension, and described as: γ = ∂

∂( )GA ni T P, ,

, where G is Gibbs free energy of the surface,

Figure 1.6. Scheme showing the two new surfaces created by cutting a cube into two rectangles.

Nanomaterials

1-7

and A is surface area. T, P, and ni are temperature, pressure, and mole number ithcomposition.

• How can surface energy be reduced?

Different known mechanisms to reduce the surface energy for a given surface with afixed surface area can take place: (i) surface relaxation, where surface atoms or ionsshift inwardly; (ii) surface restructuring through combining surface dangling bondsinto strained new chemical bonds; (iii) surface adsorption through chemical orphysical adsorption of terminal chemical species by forming chemical bonds or weakattraction forces such as electrostatic or van der Waals forces; (iv) compositionsegregation or impurity enrichment on the surface through solid-state diffusion. Formore details, the reader can refer to [3].

Surface relaxation is a well understood mechanism. Figure 1.7 schematicallyillustrates a surface atomic relaxation. For bulk materials, such a reduction in thelattice dimension is too small to result in any response of the overall crystal latticeconstant. However such inward (figure 1.7(a)) or lateral (figure 1.7(b)) shift ofsurface atoms would result in an appreciable reduction of surface energy.

Another way for surface energy reduction is chemical and physical adsorption onsolid surfaces, such as for example the chemical adsorption of hydroxyl groups onthe surface of silicon when exposed to atmosphere. Figure 1.8 illustrates threeexamples of chemical adsorption of: (a) oxygen atoms on nanocrystalline carbonfilm [17], (b) hydroxyl groups on silicon NP [18], and (c) hydrogen atoms ondiamond thin film [3]. Composition segregation is another mechanism to lower thesurface energy, however, it is unlikely to occur in a solid surface for bulk materialsbecause of the high activation energy required for such diffusion, in addition to thelarge distances. Instead, for NMs, phase segregation plays an important role in thereduction of surface energy considering the high surface energy and the shortdiffusion distances. Figure 1.8 shows HRTEM of cubic (d) and spherical (e) Fe NPsproduced by inert gas condensation methods [7]. The images were taken a fewminutes after the exposition of the sample to the atmosphere. The surface oxidationin both cases is important. Resulting in core–shell structures of the NPs. X-rayphotoelectron spectroscopy study on Fe-based NPs confirmed that after theexposition of these NPs to atmosphere, a progressive oxidation of Fe to Fe3+

occurs. For more details on this study the reader can refer to references [18, 19].From a practical point of view, the mechanisms for the reduction of surface

energy in the case of individual nanostructures and overall systems are: (i) surfacerestructuring as discussed above; (ii) formation of facet crystals. In fact, for acrystalline solid, different crystal facets possess different surface energy, therefore a

Figure 1.7. Surface energy reduction by surface relaxation. (a) Inward shift, (b) lateral shift.

Nanomaterials

1-8

crystalline particle forms facets, instead of having a spherical shape; (iii) Ostwaldripening, where smaller NPs merge to form larger ones, reducing their surface area,and then the overall surface energy. In fact Ostwald’s ripening can either widen ornarrow the size distribution of NPs depending on the experimental conditions duringthe synthesis process. In general, this process leads to the formation of polycrystal-line NPs.

Another mechanism to reduce the overall surface energy is the formation ofagglomerates. However, when small nanostructure agglomeration occurs, it is verydifficult to re-disperse them, which complicates their use as individual buildingblocks to produce the desired nanostructured materials. For this reason, it is veryimportant to find the optimum conditions to stabilize small nanostructures byreducing the total surface energy, while avoiding agglomeration of the smallnanostructures.

1.3.3 Electrostatic stabilization and steric stabilization

The stability of colloidal systems is an important subject from both the academicand industrial points of view. Colloidal systems refer to solid–liquid dispersions(suspensions), liquid–liquid dispersions (emulsions) and gas–liquid dispersions(foams), among others. As shown in figure 1.9, there are three common methodsfor colloidal particle stabilization: (i) electrostatic stabilization; (ii) steric stabiliza-tion; and (iii) a mixed electric and steric (electrosteric) stabilization.

Electrostatic stabilization and steric stabilization are the two major mechanismswidely used for NP stabilization. Systems using electrostatic stabilization arekinetically stable, whereas systems using steric stabilization are thermodynamically

Figure 1.8. Examples of mechanisms for the reduction of surface energy.

Nanomaterials

1-9

stable. The term ‘nanoparticles’ is not limited to nanostructures with sphericalshape, but also includes other nanostructures such as nanorods and nanofibers.

In colloidal science, the milestone for understanding the interaction energybetween suspended particles is the DLVO theory, named after Derjaguin,Landau, Verwey and Overbeek in reference to their pioneering work [21–23].

According to this theory, the interparticle energy depends on the sum of attractiveand repulsive interactions, which are both function of the particle-to-particledistance. The Van der Waals attractive force between two particles of the samematerial promotes the aggregation of suspended particles, whereas the repulsivecomponent of the DLVO theory can be explained by the electric double layerformation on the particle surface immersed in a polar fluid. In fact, when immersedin a polar fluid, the NP develops a surface charge depending on the chemicalcomposition of the particle. For example, in the case of metal oxides, the chargeformation is due to the hydroxylation of their surfaces, which can then react witheither H3O

+ or OH− in water [24]. The consequent protonation or deprotonation ofthe surface group results in the positive or negative charge on the particle surface. Inthe case of functionalized particles, (e.g. carboxylated particles) dispersed in water, anegative surface charge is developed on the particle surface by the ionization of the –COOH groups. Because of the surface charge, an electrostatic potential is created inthe proximity of the particle, and a concentrated layer of counter ions, known as theStern layer, is formed. Moreover, a diffuse layer of anions and cations is formedbeyond the Stern layer (figure 1.10(a)). The charged surface, the Stern layer and the

Figure 1.9. Schemes illustrating the concepts of electrostatic stabilization (a), steric stabilization (b), andelectrosteric stabilization (c). Adapted from [20] under CC BY 3.0.

Nanomaterials

1-10

diffuse layer constitute the three levels of the electric double layer typically observedaround a particle immersed in a polar fluid.

It is worth noting that the strength of the surface potential can be adjusted byexperimentally tuning the pH value of the suspension. Based on the DLVO model,when the electrostatic component is predominant, particles repel each other, and the

Figure 1.10. (a) Electric double layer in a polar liquid. (b) Interaction energy for the stable dispersion ofparticles in a liquid medium, according to the classical DLVO theory. Adapted from [24] under CC BY 0.3.

Nanomaterials

1-11

potential barrier prevents the particles from agglomerating in the primary minimum(figure 1.10(b)). On the other hand, if the van der Waals contribution dominates,particles can overcome the potential barrier and agglomerate in the primaryminimum. From an experimental point of view, the effect of interaction energiesbetween particles can be measured by zeta-potential (ζ). This potential depends onthe chemical properties of both particle surface and solution composition (pH). ThepH value corresponding to ζ = 0 mV is known as the isoelectric point (IEP) and,when the magnitude of the zeta-potential is close to the IEP or smaller than a certainthreshold (e.g. ζ ≈ 10 mV for Al2O3–water suspensions) [25] the repulsive forcesbetween particles are weak and particle agglomeration occurs. The measurement ofzeta-potential offers a link between experiments and theoretical background. Inparticular, zeta-potential is often associated with the value of electrical surfacepotential found in the DLVO theory [3, 24, 26, 27].

Although DLVO theory is considered as a consolidated theory for modellingcolloidal interactions, several works have been carried out for including steric andhydration contributions in the base theory. In fact, such nanoscale effects canstrongly alter the interaction energy between suspended NPs and thus influenceaggregation kinetics [24].

Figure 1.11(a) illustrates the basis of the steric stabilization based on thepolymeric surface functionalization of the particles. Compared to electrostaticstabilization, this method offers an additional advantage as it is not electrolytesensitive and is suitable for multiple phase system. Briefly, considering two solidparticles coated with polymers as schematically illustrated in figure 1.11(a), when apolymer is added to the suspension containing the colloidal particles, it can interactwith solid surface forming an irreversible bind to the solid surface by one end only,as shown in figure 1.11(b)(1), or adsorbed weakly at random points along the surfaceof the particles (figure 1.11(b)(2)). These interactions take place either by formingchemical bonds between surface ions or atoms on the solid and the polymermolecules, or by week physical adsorption.

Figure 1.11. Illustration of the concept of steric stabilization in the case of colloidal solid particles.

Nanomaterials

1-12

If two particles (coated with a polymer) approach one another to reach a distance‘h’ between the surface of the particles, when d < h < 2d, where d is the thickness ofthe polymer layer (figure 1.11(c)(1)–(2)), two interactions take place: (i) interactionbetween the surrounding fluid and the polymer, and (ii) interaction between the twopolymer layers. However, there will be no interaction between the polymer layer ofone particle and the solid surface of the opposite particle. In a good solvent, in whichthe polymer expands, if the coverage is less than 50%, the two polymer layers tend tointerpenetrate reducing the space between polymers resulting in a reduction of thefreedom of the polymers (figure 1.11(c)(1)); this leads to a reduction of entropy(ΔS < 0). Assuming the change of enthalpy due to such interpenetration is negligible(ΔH ∼ 0), the Gibbs free energy of the system (ΔG = ΔH − TΔS) become positive, sothat the two particles repel one another resulting in a stable system.

If the polymer coverage on the particle surface approaches 100%, compression ofthe polymer layers occurs when the particles approach each other (figure 1.11(c)(2)).As a consequence, the polymer coils-up in both layers and the Gibbs free energy(ΔG) increases. Then the particles repeal each other to decrease the overall Gibbsfree energy.

An effective steric stabilization relies on the following criteria: (i) the particlesshould be completely covered by the polymer to avoid van der Waals attractionbetween the uncovered surfaces, or a polymer bridging when the polymer becomessimultaneously adsorbed on two or more particles; (ii) the polymer should bestrongly adsorbed or ‘anchored’ to the particle surface; (iii) the stabilizing chain ofthe polymer should be highly soluble in the medium, independently of the temper-ature of the surrounding medium, and/or the presence of electrolytes; and (iv) thethickness of the adsorbed polymer layer thickness should be sufficiently large tomaintain a minimum interspace between the functionalized surfaces, particularly inthe case when a high stability of colloidal suspension is required [28].

1.3.4 Electrosteric stabilization

Electrosteric stabilization is a combination of electrostatic and steric stabilization(figure 1.9(c)). Specifically, this type of stabilization uses adsorbed or graftedpolymers like in steric stabilization. However, the adsorbed polymers have non-negligible electrostatic charge resulting in the formation of a significant chargeddouble-layer. The most common approach to electrosterically stabilized colloids isby adding a polymer with an ionizable group that is dissociated in the solvent tocreate charged polymers. Therefore, both electrostatic and steric stabilizationsdepend on the pH, dielectric properties, and ionic strength of the solvent. A deepunderstanding of the electrosteric phenomenon is both intriguing and difficult due tothe large number of system parameters involved, such as the electrical properties ofthe solvent, grafted layer density, and polyelectrolyte properties of the graftedpolymer [29, 30].

References[1] Feynman R P 1960 There’s plenty of room at the bottom Eng. Sci. 23 22–36

Nanomaterials

1-13

[2] Drexler K E 1990 Engines of Creation: the Coming Era of Nanotechnology (Oxford: OxfordUniversity Press)

[3] Cao G and Wang Y 2011 Nanostructures and Nanomaterials 2nd edn (Singapore: WorldScientific)

[4] Gorman C R 2014 The interface: IBM and the transformation of corporate design,1945–1976 J. Design History 27 101–2

[5] Service R F 2001 Science 293 782–5[6] Schön J H, Meng H and Bao Z 2001 Science 294 2138–40[7] Benelmekki M 2015 Designing Hybrid Nanoparticles (IOP Concise Physics Collection) (San

Diego, CA: Morgan & Claypool)[8] Takashiri M, Tanaka S, Takiishi M, Kihara M, Miyazaki K and Tsukamoto H 2008

J. Alloys Compd. 462 351–5[9] Hummers W S and Offema R E 1958 J. Am. Chem. Soc. 80 1339[10] Binns C 2009 Handbook of Metal Physics: Metallic Nanoparticles ed J Blackman 1st edn

(Amsterdam: Elsevier) ch 3[11] Jana A, Scheer E and Polarz S 2017 Beilstein J. Nanotechnol. 8 688–714[12] Benelmekki M, Bohra M, Kim J H, Diaz R E, Vernieres J, Grammatikopoulos P and

Sowwan M 2014 Nanoscale 6 3532–5[13] Vila-Fungueiriño J M et al 2015 Front. Phys. 3 38[14] Wang Y, Chen W, Wang B and Zheng Y 2014 Materials 7 6377–485[15] Mu C and He J 2011 Nanoscale Res. Lett. 6 150[16] Nordlund K 2014 Lecture Notes: ‘Nanoscience I: Downscaling of classical laws makes nano

different’ University of Helsinki[17] Kim J-H and Benelmekki M 2018 Emerging Applications of Nanoparticles and Architecture

Nanostructures ed H Makhlouf and A Barhoum (Amsterdam: Elsevier) ch 18 pp 553–74[18] Benelmekki M, Vernieres J, Kim J H, Diaz R E, Grammatikopoulos P and Sowwan M 2015

Mater. Chem. Phys. 151 275–81[19] Benelmekki M and Sowwan M 2015 Handbook of Nano-Ceramic and Nano-Composite

Coatings and Materials ed H Makhlouf and D Scharnweber (Amsterdam: Elsevier) ch 9pp 207–23

[20] Tchalala M R, Anjum D H and Chaieb S 2016 J. Phys.: Conf. Ser. 758 012020[21] Derjaguin B and Landau L 1941 Acta Physicochim. URSS 14 633–52[22] Verwey E and Overbeek J T G 1955 J. Colloid Sci. 10 224–5[23] Hunter R J 2001 Foundations of Colloid Science (Oxford: Oxford University Press) pp 222–4[24] Cardellini A, Fasano M, Bigdeli M B, Chiavazzo E and Asinari P J 2016 Phys. Condens.

Matter 28 483003[25] Pastoriza-Gallego M, Casanova C, Paramo R, Barbes B, Legido J and Pineiro M 2009 J.

Appl. Phys. 106 064301[26] Kulshreshtha A K, Singh O N and Wall G M 2009 Pharmaceutical Suspensions: From

Formulation Development to Manufacturing (Berlin: Springer)[27] Hiemenz P C 1977 Principles of Colloid and Surface Chemistry (New York: Marcel Dekker)[28] Tharwat F 2007 Tadros Colloid Stability: The Role of Surface Forces (New York: Wiley)[29] Fritz G, Schadler V, Willenbacher N and Wagner N J 2002 Langmuir 18 6381–90[30] Kraynov A and Muller T E 2011 Concepts for the stabilization of metal nanoparticles in

ionic liquids Applications of Ionic Liquids in Science and Technology ed S Handy (London:InTech)

Nanomaterials

1-14