List of presentations and abstracts:

• Characterizing Mesoscale Structure and Phenomena (two sessions)
• Predicting Mesoscale Structure and Phenomena (three sessions)
• Applications: why we care about mesoscale phenomena, and how we control it
  
  

Characterizing Mesoscale Structure and Phenomena in Fluid Systems I

•   Introductory Remarks - Fiona Case

•   Small-angle scattering characterization of block copolymer micelles and lyotropic liquid crystals. P. Alexandridis

Addition of selective solvents to a block copolymer of fixed composition provides extra degrees of freedom for controlling the equilibrium morphology and, hence, structure/property relationships. Diverse ordered (lyotropic liquid crystalline) structures, such as cubic, hexagonal, and lamellar, as well as micellar solutions can be formed. Using examples drawn from our research on poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymers, we will discuss structural information that can be obtained on micelles and liquid crystals from small angle neutron and X-ray scattering, respectively. In addition to determining the shape and characteristic lengthscales of the block copolymer assemblies, we have used scattering to assess the (i) degree of block copolymer segregation, (ii) partitioning of solvent mixtures in domains formed by different blocks, (iii) alignment, orientation transitions, and structural transformations occurring under shear, and (iv) structure of surface-adsorbed assemblies. Experimental findings are compared to (and confirmed by) mean-field theoretical predictions.

•   Structure and composition of mixed surfactants at interfaces and in solution. J. Penfold

The use of specular neutron reflection and small angle neutron scattering to investigate the composition and structure of mixed surfactants at interfaces and in micelles will be described. Results from mixed anionic nonionic, cationic-nonionic, and nonionic-nonionic surfactants at the air-solution, liquid-solid, and oil-water interfaces, and in micelles will be compared with theoretical predictions. At the liquid-solid interface, the role of specific surfactant/surface interactions will be discussed. At the oil-water interface, partitioning of surfactant into the oil phase, and the solubilisation of oil into mixed micelles will be discussed. Detailed structural information on the mixed surfactant layer at the air-water interface will be presented. Comparison with the structure of the pure component monolayers will highlight limitations of some current theories of surfactant mixing. The structure of mixed surfactant micelles, obtained by small angle neutron scattering measurements, will be compared with recent theoretical predictions, and the effects of electrolyte and solubilised alkane described.

•   Mesoscale structure of adsorbed liquid films in ordered nanoporous silica studied by in-situ SANS. G. H. Findenegg, A. Schreiber, E. Hoinkis

Pore filling of mesoporous solids by vapor adsorption commonly involves the formation of a liquid-like film at the pore wall followed by pore condensation. We have studied this process in MCM-41 type ordered mesoporous silica with cylindrical pores of uniform size by in-situ small-angle neutron scattering. SANS curves exhibit Bragg peaks resulting from the 2D hexagonal packing of the pores. The intensity of the individual peaks decreases or increases in a specific way with the extent of pore filling. These features can be reproduced by a model in which the thickness of the adsorbed film is taken into account by a form factor F(R,r) of cylindrical objects, with t=R-r the thickness of the adsorbed film. This formalism was used to study the mesoscale structure of nitrogen adsorbed films as a function of the relative pressure and of the pore radius R of MCM-41 type materials of pore widths from 3 to 10 nm. We derive direct information about the curvature effect on the thickness of liquid-like adsorbed films at this mesoscopic scale.

•    X-ray scattering studies of long-chain n-alcohol monolayers at the water-hexane interface . M. L. Schlossman, A. M. Tikhonov

X-ray surface scattering is used to study molecular ordering and phase transitions in soluble monolayers of n-alcohols (CH ₃ (CH ₂) _m-1 OH, where m=20, 22, 24, and 30) adsorbed at the water-hexane interface. In contrast to well-ordered fluorinated monolayers previously studied, these monolayers have a distinctive type of disorder. The monolayer molecules are oriented nearly perpendicular to the interface and are nearly all-trans. Penetration of hydration water molecules into the region of the head group must be accompanied by head group disorder along the interfacial normal. The region of the tail group next to the head group is nearly close-packed while the region adjacent to the hexane is more disordered. Upon heating, the monolayers undergo a solid to gas transition. Near the transition, the temperature dependence of the coverage of the low temperature phase can be analyzed by a functional form consistent with a critical transition as proposed by theory.

•   Cryo-TEM study of self-aggregation of sodium lithocholate single-molecular walled nanotubules. Y. Talmon, J. Schmidt, P. Terech

We describe a recent study of nanoscopic self-aggregation in aqueous solutions of sodium lithocholate, leading to the formation of nanotubules. Using modern cryogenic temperature transmission electron microscopy (cryo-TEM) augmented by digital imaging (the state-of-the-science will be briefly described) and small-angle x-ray scattering (SAXS) we have shown that micrometer-long nanotubules form spontaneously with monodisperse cross-sections (Do=52 nm, Di=49 nm) in alkaline aqueous solutions of sodium lithocholate (SLC). The shell of these tubules, 1.5 nm thick, is made of a monomolecular sheet of the bile salt. Such SLC assemblies could be used for the development of functional materials based on 1-D structures, and as supramolecular templates for the synthesis of inorganic materials in nanotechnology. Time-resolved cryo-TEM has elucidated the mechanism of formation of those nanotubules. Interesting intermediate nanostructures are multi-walled tubules of a wide range of diameters and lengths that mature into uniform micron-long single-walled nanotubules.

•   Self-assembly of amphiphilic substituted poly(para-phenylenes) in aqueous surfactant solutions. G. H. Findenegg, T. Fütterer, T. Hellweg, J. Frahn, A. D. Schlüter, C. Böttcher

2,5-disubstituted poly(para-phenylenes) with one nonpolar substituent R1 and one polar substituent R2 on each monomeric unit represent an interesting class of amphiphiles in which the border between the hydrophilic and hydrophobic part of the molecule runs along its stiff backbone. We have studied the self-assembly of a poly(para-phenylene) oligomer, PPn (n=12), with substituents R1=-C12H25 and R2=-CH2(OC2H4)3OCH3 in the pure state and in aqueous surfactant solutions, using light scattering, SANS, and cryo-TEM. This compound is soluble in aqueous solutions of nonionic surfactants such as C8E4, where it forms elongated stiff aggregates (contour length ca. 500 nm, diameter 5.5 nm). cryo-TEM pictures indicate a bilayer structure of the PP12 molecules in the aggregates. The specific role of the surfactant in these aggregates is not yet understood. Dynamic light scattering data from the aqueous PP12-C8E4 solution can be modelled by an intermediate scattering function for Zimm dynamics by Pecora. These calculations indicate that the aggregates exhibit a high persistence length compared to their contour length.

Further Information about the speakers in this session is available here

Characterizing Mesoscale Structure and Phenomena in Fluid Systems II

U. Nobbmann, Presiding

•   Introductory Remarks - Fiona Case

•   Characterization down to nanometers: Light scattering from proteins & micelles. U. Nobbmann

Dynamic light scattering can be used to characterize biomolecules in solution. Laser light is guided through a sample and the scattered light detected as single photons. Analysis of the light intensity fluctuations yields the diffusion coefficient and hydrodynamic radius of the scattering objects. This technique can be applied from peptides ( ~ 1nm ) to assembled structures like viruses ( ~ 10 nm ) and up to larger aggregates ( ~ mm ). A similar size range is covered by surfactant systems. Above the critical micelle concentration detergent molecules assemble into micelles. Detergents can also increase solubility of amphiphilic molecules such as membrane proteins by covering the lipophilic parts. Light scattering allows the determination of micellar size distributions in solution.

•   Characterizing mesoscale structure and phenomena in fluids using NMR. P. Stilbs

Nuclear magnetic resonance (NMR) recently celebrated its 50-year anniversary. No other physico-chemical method comes close to rivalling it with regard to versatility as a general, quantitative and detailed source of information at the molecular level. It also provides information on structure and dynamics. Pulsed gradient spin echo NMR (PGSE-NMR) and spin relaxation methods can be used to study the dynamic behavior of mesoscale structures. These techniques generally complement each other and will be illustrated by case studies like surfactant/polymer or surfactant/protein aggregation, and of transport in associative polymer solutions with different hydrocarbon tails. NMR diffusion measurements also provide a unique method for characterizing mixed micelle surfactant compositions. Through component-resolved electrophoretic NMR techniques one can furthermore provide insights into ionic micelle surface structure and counterion binding which are valuable for parameterizing and validating mesoscale modeling methods.

•   Sculpting nano-scale liquid interfaces. R. C. Bell , H. Wang, M. J. Iedema, J. P. Cowin

Mesoscale-structured liquids are difficult to understand because their geometry is often poorly known. We create “structured liquids” using molecular beam epitaxy at low temperature, which have well defined, sharply modulated structures. With these we mapped the solvation potential of ions near the oil/water interface. We also show how nanometer films of glassy 3-methylpentane (3MP) are much less viscous at the vacuum-interface, using ion mobility to probe the spatially varying flow properties with a resolution of 0.5 nm. The amorphous 3MP films are constructed using molecular beam epitaxy on a Pt substrate. Ions are then gently deposited at specific locations within the film. As the film is heated above the bulk glass transition temperature of 3MP, it becomes increasing fluid and the resulting ion motion is monitored electrostatically. By placing the ions at increasing distances from the interface, the fluidity perturbation was found to persist over 2.9 nm.

•    Aggregation, gelation and aging in colloidal suspensions - time-resolved light and neutron scattering experiments P. Schurtenberger , H. Bissig, R. Vavrin, A. Stradner, F. Scheffold, V. Trappe, L. Cipelletti

We present a time-resolved study of the aggregation, sol-gel transition and subsequent aging in concentrated colloidal suspensions. We use diffusing wave spectroscopy (DWS) to obtain quantitative information about the microscopic dynamics all the way from an aggregating suspension to the final gel, thereby covering the whole sol-gel transition. In order to obtain additional information on the corresponding structural changes we have designed a combined SANS-DWS experiment. This allows us for the first time to simultaneously measure both the time evolution of the local dynamics as well as the microstructure as the aggregation and gelation proceeds. Moreover, we compare the SANS results with Monte Carlo computer simulations of stable and destabilized colloidal suspensions.

•   Aging phenomena in colloidal systems: Rheology, microrheology, and thermodynamics E. E. Pashkovski

Concentrated colloidal systems such as suspensions, emulsions, gels and pastes display complex and very intriguing behavior reflecting their metastability and structural disorder. Their rheological response depends on sample age and is similar to the response of molecular and spin glasses. This suggests an approach for studying aging phenomena in these soft colloidal glasses. We employ a thermodynamic description of aging by analyzing the violation of fluctuation-dissipation theorem combining rheological and diffusing-wave spectroscopy measurements. The mesoscale and macroscopic dynamic behaviors are strongly disentangled on the time scale comparable with sample age. On the very short time scale, however, no violation is observed. These findings agree with recently published results on aging of soft glasses and, we argue, are widely applicable, and system-independent. We further characterize the structural aspects of aging by using tracer particles with various sizes. The change in mesoscale structure measured using these techniques is shown to correlate with macroscopic aging phenomena. 

•   Nanoscale vs macroscale friction in polymers and small-molecule liquids: Studies of anthracene rotation in poly(isobutylene) and poly(dimethylsiloxane). M. M. Somoza, M. I. Sluch, M. A. Berg

In small-molecule liquids, hydrodynamic models using the macroscopic viscosity work well even for subnanometer sized objects. However, polymers are expected to show reduced friction for objects smaller than the polymer chain. We have used the rotation time of dissolved anthracene to measure the "nanoviscosity" in poly(isobutylene) (PIB) and poly(dimethylsiloxane) (PDMS) as a function of polymer length. The range of lengths extends from the small-molecule limit to the entangled polymer. A difference between the macro- and nano-viscosities develops abruptly as the polymer length increases. The conventional view that a simple ratio of solute-to-solvent size governs the breakdown of simple hydrodynamics is not supported. We suggest that the development of a region of unique nanoviscosity is determined by the dynamic rigidity of the solvent, i.e., the probability that a solvent molecule will undergo a change in torsional conformation during the rotational time of the solute.

Further Information about the speakers in this session is available here

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Predicting Mesoscale Structure and Phenomena in Fluid Systems I

•   Introductory Remarks. Fiona Case

•   Dynamics of micro- (and nano-) fluidics: From basic concepts to applications. H. A. Stone

The ability to transport and manipulate fluids on micron and smaller length scales has triggered a wide range of scientific investigations and technological applications. Microfluidic devices allow handling of small fluid volumes, fast response times, selective addressing of the cellular scale, and they allow for sensing and flow control. There are many recent studies of transport processes in microfluidic devices and network, including mixing, reactions, separations, etc. In this talk we will survey basic principles useful for understanding and describing microflows, as well as outlining some of their applications in the areas of mixing, multiphase flow, and electrically driven transport.

•   Modeling structure and rheological behavior in mesoscale fluid systems. P. Coveney

Mesoscale simulation techniques based on dissipative particle dynamics (DPD) provide new capabilities for predicting hydrodynamic properties of what has recently become known as "soft condensed matter", including binary and ternary amphiphilic (surfactant containing) fluids, colloids and polymers. A key to their successful application to predict properties of real systems is a robust strategy for generating DPD input parameters for specific materials. An overview of these methods will be followed by applications examples showing how DPD was used to predict the rheological behavior of industrially relevant surfactant and colloid systems under flow.

•   Application of the dissipative particle dynamics simulation method to materials physics problems in polymer and surfactant science. M. G. Noro

Dissipative particle dynamics (DPD) is an important new simulation methodology with a broad range of applications to the simulation of complex fluids. This contribution will introduce the DPD method and illustrate its use with a variety of examples drawn from our work in this area. In our group it has been used to study the phase behaviour and kinetics of order-disorder transitions in block copolymers, thermodynamics and dynamics in polymer  and surfactant  solutions.

•   Dynamics of intrinsically curved DNA fragments in gels. U. Mohanty

We have explicitly solved the long standing problem of a quantitative predictive model that describes the electrophoretic mobility patterns of circularly-permuted DNA molecules, all having the same length but with the bend positioned differently in each, in polyacrylamide gel of various concentration. The bends are due to short stretches of adenines, i.e. A-tracts, which were repeated in phase with the helical repeat. The model takes into account in an approximate way polyelectrolyte effects such as condensed and screened counterions, coulombic end effects, salt concentration, pH of the buffer, screening of the hydrodynamic interactions, flexibility of the molecule, concentration of the gel, as well as the characteristics of the interactions of the gel with the curved DNA. The predictions (no parameters) are in excellent agreement with the experimental data of Crothers and coworkers and of Thompson and Landy. We have generalized our model to describe the electrophoretic mobility of phased A-tracts.

Further information about the speakers in this session is available here

Predicting Mesoscale Structure and Phenomena in Fluid Systems II

S. C. McGrother, Presiding

•   Introductory Remarks. Fiona Case

• Field theory in the computer: complex fluids. A. G. Moreira , G. H. Fredrickson

In recent years, due to the enormous increase of cheap computer power, there has been a growing interest in the simulation of complex fluids. The main advantage of simulations over analytical methods is that the former allows the theoretical study of complicated systems without introducing approximations that make the problem analytically tractable. This means that, while one can focus on some key aspects of the system (by using an appropriate model), one does not loose details in the treatment, leading to results/predictions that can be better applied to reality. In general, when one wishes to tackle a particular system (eg. a polymer solution or a colloidal suspension) one is confronted with an important question: which method is the most appropriate for the problem at hand? While most simulations to date are based on particles, it is possible to treat a fairly large class of complex fluids within a field-theoretic formalism. This provides an alternative approach to the simulation of complex fluids. We will outline these methods and show preliminary results obtained for some polymer systems, ranging from the dilute to the concentrated regimes.

•   Simulation and theory of macromolecular self-assembly dynamics. A. Sevink, H. Fraaije

Rational design of nano patterned self-assembly materials is receiving increased attention, with diverse applications in encapsulated drug delivery systems, microreactors and smart solar cells. We consider two recent advances in the mesoscale simulation of soft polymer materials. In the first application, we studied pattern formation in thin films of cylinder-forming SBS triblocks copolymer. With only two parameters, the film height and the polymer-wall interaction, we were able to match both simulation and experimental phase diagram. We found that deviations from the bulk structure can be identified as surface reconstructions. Our results give evidence for a general mechanism: the interplay between the strength of the surface field and the deformability of the bulk structure determines how the system arranges in the vicinity of the surface, and leads to either orientation of the bulk structure or surface reconstruction. In the second application we considered polymer vesicle formation, starting from homogeneous polymer droplets in solvent. We found, varying the initial droplet radius and the ratio of polymer blocks, tiny gels that are distorted analogons of the Archimedean and Platonic solids. An interesting finding is a 'buckyball' surface structure, which follows the same geometrical rules as C60 fullerenes, but with a twist: the nanogels are soft.

• Mesoscale modeling: industrial applications. S. C. McGrother , G. Goldbeck-Wood

The importance of mesoscale phenomena is increasingly appreciated in industry. Cutting-edge techniques for modeling such length and time scales are increasingly validated and available in standard software packages with various hardware alternatives. Accelrys offers DPD (dissipative particle dynamics) and MesoDyn. Both tools coarse-grain the familiar atomistic representation of the molecule to gain orders of magnitude in both length and time scale. The chemistry of the system is captured through effective potentials based on the energy of mixing of the binary pairs in the system. The methods yield structural and dynamic information on the phase morphology and can be used as input to finite element analysis. In this talk, the accuracy of such tools is assessed with particular emphasis on the communciation between the various length scales. Important case studies are discussed, recent advances are presented and ideas for future applications and directions are suggested.

•   Mesoscale Level Modeling of Siloxane-Based Nanoparticles and Nanocomposites. S. Grigoras

The nanoscale materials gained recently considerable amount of interest, since they are expected to provide unique properties on the account of their finite small size. As components of various sub-ensembles, or nano-composites, it is important to have knowledge of the properties of the individual nanopaticles that can further be used to evaluate the properties of the entire system. Resins technology provides a broad range of nanoparticles with various structures, shapes and sizes. The objective of this work is to evaluate mechanical properties of various structures and indicate what type is more promising to be the target for synthesis or isolation. The method presented in this paper derives the elastic constants from the shape fluctuations that are obtained from Molecular Dynamics, or Monte Carlo atomistic simulations carried out with single nanoparticle in vacuum at constant temperature. The results obtained from atomistic simulations are then used to evaluate mechanical properties at mesoscale level, of such nanostructures in polymeric matrices using PALMYRA software. This method is based on Finite Element Analysis, under periodic boundary conditions. The results are discussed for random and oriented particles, in context of the ultimate properties predicted from the continuous approach. The mesoscale approach was also used to evaluate the mechanical properties of porous glasses, as a function of the size of the pores and their fraction volume. Overall it is concluded that the chemical structure of the silica framework, and the type of substituents are the primary factors, in addition to the volume fraction of each phase, that control the properties of a heterogeneous system.

Further information about the speakers in this session is available here

Predicting Mesoscale Structure and Phenomena in Fluid Systems III

•   Introductory Remarks. Fiona Case

•   Self-assembled peptide tapes: theory and experiment on self-assembly, kinetics and rheology T. C. B. McLeish, A. Aggeli, P. Mawer, I. Nrykova, A. N. Semenov, M. Bell, N. Boden

Three artificial peptides form the raw material for a study of their self-assembly into a hierarchy of tapes, fibrils and fibres at the nano-scale. A small number of parameters capturing the energy of association at different scales supplies a statistical mechanical model of the emergence of the scale of structures with increasing concentration. The results successfully account for observations from spectroscopy, scattering, and microscopy. Dynamic light scattering and rheology introduce more intriguing puzzles into the picture, but suggest that the systems may behave in some circumstances as model stiff polymers.

•   How well can a simple molecular theory predict self-assembled microstructures in multicomponent systems involving surfactants, oil, water, alcohol, and electrolytes? R. Nagarajan

Attempts to predict the formation of self-assembled microstructures and the phase behavior of these systems continue to develop along different lines, either based on theory or computer simulations. Many practical systems of interest consist of multiple components such as one or more surfactants, alcohol, oil, electrolytes, polymers, solvents as well as water. Over the years, we have constructed a relatively simple molecular theory to describe a variety of self-assembling systems such as micelles, vesicles, solubilized aggregates, and microemulsions. The main features of the theory are the use of phenomenology to identify important free energy contributions relevant to aggregation, formulation of analytic free energy expressions invoking molecular properties to represent these free energy contributions, a unified approach to treating the variety of self-assembled systems, applicability to multicomponent systems, and the relative simplicity of the computations involved. The theory requires very few molecular constants and does not incorporate any experimental information pertaining to self-assembly; the theory is truly a priori predictive. The theoretical predictions are in reasonable agreement with experiments. The theory is also extremely stringent in the sense that although there are just few molecular constants to represent a surfactant, yet they should lead to accurate prediction of a variety of measurable properties.

•   Complementary use of simulations and free energy models for CTAB/NaSal Systems. A. McCormick

The practical formulation of surfactant products often requires additives that help regulate physical properties by varying mesoscale structure, such as the preferred micellar shape. For example sodium salicylate is added to aqueous solutions of CTAB to convert spherical micelles into worm-like micelles, thus producing an effective drag-reducing agent. Using this example we will describe how a model that combines aspects of free energy models with simulations can predict the changes in ordering of the amphiphiles within micelles of different curvature which are responsible for this transformation. The results agree with some experimentally observed trends, and help to account for others. Comparison of this approach with predictions based only on free energy models highlight the significance of accounting for intramicellar ordering in calculating micelle free energies. In general, such a model can predict the effect of inclusion of other organic additives into micellar structures.

•   Monte Carlo simulation and theory of self-assembled networks. J. T. Kindt

Linear self-assembly interrupted by junctions is characteristic of worm-like micellar systems, which may form networks at moderate volume fraction. This general phenomenon is studied by mean-field theory and Monte Carlo simulation. First, the theory originally formulated by Tlusty and Safran is revisited from the perspective of end-interior interactions (T-junctions) rather than interactions between three chain ends (Y-junctions). While the final results are equivalent, a new perspective is gained in which the thermodynamic transition that sometimes accompanies the network-forming transition may be easily interpreted as a conventional gas-liquid transition. Simulation results for hard spheres self-assembling into semiflexible chains with T-junctions are in qualitative agreement with mean-field theory. In contrast, for a comparable flexible chain model, the expected gas-liquid transition is apparently suppressed by intra-chain junction or loop formation. The effects of loop formation on the phase diagram are explored using a simple modification of the mean-field theory.

•   Unstructured protein domains and polymer brush unteractions determine neurofilament organization in nerve axons. S. Kumar, J. H. Hoh, M. E. Paulaitis

Neurofilaments (NFs) have been proposed to interact with one another through mutual steric exclusion of their unstructured C-terminal "sidearm" domains, producing order in axonal NF distributions and conferring mechanical strength to the axon. Here we apply theory developed for polymer brushes to examine the relationship between the brush properties of the sidearms and NF organization in axons. We first show that the NF distributions may be represented by a single pair potential of mean force. We then conduct two-dimensional Monte Carlo simulations of NF cross-sectional distributions, imposing purely repulsive interaction potentials in which the sidearms are represented as polyelectrolyte chains, and attractive cross-bridging interactions. We find that NF structure is sensitive to changes in brush thickness mediated by chain charge, consistent with experimental observations that sidearm phosphorylation regulates interfilament spacing. Attractive cross-bridging interactions contribute only modestly to structure for moderate cross-bridging and leads to NF aggregation for extensive cross-bridging.

Further information about the speakers in this session is available here

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Applications: why we care about mesoscale phenomena, and how we control it

C. U. Thomas, Presiding

•   Introductory Remarks. Fiona Case

• Structure, properties, and applications of mesoscale materials D. A. Weitz

This presentation will describe the physics of soft condensed matter, materials which are easily deformed by external stresses, electric, magnetic or gravitational fields, or even by thermal fluctuations. These materials typically possess structures which are much larger than atomic or molecular scales; the structure and dynamics at the mesoscopic scales determine macroscopic physical properties. The goal of our research is to probe and understand the relationship between mesoscopic structure and bulk properties. Examples will include both synthetic and biological materials, and will extend from fundamental physics to technological applications, from basic materials questions to specific biological problems

•   The importance of mesoscopic structures in the development of advanced materials. C. U. Thomas, G. Caldwell, S. Mohanty, M. Freedman

As part of an industrial laboratory, we face the challenge of developing advanced materials by manipulating the relation between the chemical structure and the desired performance. Many of the processes governing these relations are clearly beyond the limit of atomistic scales. They involve length and time scales from nanometers to microns and from nanoseconds to microseconds. It is then imperative to understand the basic principles that govern these mesoscopic systems. Our laboratory ,The Advanced Materials Technology Center, contributes to the innovation process via the utilization of novel technologies, including computational modeling, to control the desired material behavior. We face many challenges in the area of blends/compatibilizers, miscibility, nanocomposites, colloidal suspensions, complex fluids, and surface modification. This presentation will illustrate some of industrial relevant systems used in our industrial, health care, and specialty materials markets.

•   Impact of micellar strucure on rheology and performance in superwetting cleaners. G. Broze

Some macroscopic properties of multi-component systems are better described by the structure of their assemblies, rather than by the chemical functions of their ingredients. This is particularly the case for the rheology and solubilizing power of surfactant systems. Fluid solutions of ether sulphates can be transformed into visco-elastic gels by the simple addition of an electrolyte; oil uptake capacity of micro-emulsions depends more on micelle structure than on the nature of the surfactants. A fascinating increase in soil lifting kinetics can be observed by controlling carefully the concentration of only three ingredients, none of which are classical surfactants. Indeed, a mixture of water, an ester and a hexanol polyether formulated in the vicinity of a thermodynamic tri-critical point lifts tar soil in only a few seconds, while compositions further apart from the tri-critical point operate less rapidly, even if they are richer in "actives".

•   Self assembly of small molecules and macromolecules in compressible liquid and supercritical CO2. J. M. DeSimone,  S. L. Folk, J. D. Polley, M. Adam, M. Rubinstein

•   Emulsions or microemulsions? Phase diagrams and their importance for optimal formulations I. Johansson, O. B. Ho

Mesoscale is defined as 10^-9 to 10^-7 m. When mixing oil, water and suitable surfactants you will produce droplets of oil in water, or water in oil, stabilized by the surfactants in the range of 3x10 ^-9 to 10^-6 or larger. If your droplets are 3-100nm, and thermodynamically stable, they will constitute a microemulsion. If they are larger they will form an emulsion, which by definition is a non-equilibrium system prone to collapse and phase separate given enough time. Depending on your application you may want either of these two systems, but how do you control which you get? One way is to study the quasi ternary phase diagram. By keeping the oil/water ratio constant and varying the concentration and nature of your surfactant(s) the microemulsion phase, Winsor I, Winsor II, Winsor III and Winsor IV areas can be located, the so called Kahlweit fish. This knowledge can then be used to construct water-dilutable one phase microemulsions, optimize cleaning formulations, and to make emulsions with small droplets without using too much shearing devices. In this presentation advantages, disadvantages, and examples of different uses along the lines sketched above will be given.

Further information about the speakers in this session is available here

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