Micellar Networks - Implications for Rheology and Biology

Book The 82 ACS Colloid and Surface Science Symposium Page 1 of 321 Plenary Lecture I: Prof. Eric Kaler Presider: Orlin D. Velev North Carolina State University, Raleigh, NC Presider: Peter K. Kilpatrick University of Notre Dame, Notre Dame, IN 1. Micellar Networks Implications for Rheology and Biology Eric W. Kaler, Stony Brook University, Stony Brook, NY Many nonionic surfactants form micellar networks in water over a range of compositions and conditions, and theory suggests that the presence and nature of these networks is closely related to the presence of miscibility gaps in the phase diagram. The micelles can be directly observed by cryogenic transmission electron microscopy (cryo-TEM) and quantified by small-angle neutron scattering measurements. Convenient experimental systems with which to explore the features of such networks include alkyl monoglucosides surfactants and various additives. The temperature dependence of the phase separation observed in the binary glucoside -water mixture is explained in terms of the average curvature of the surfactant aggregate, and on the thermodynamic trade-off of micellar endcaps and junctions. As the phase boundary is approached, junctions become energetically more favorable than end-caps, and eventually the network becomes saturated. The miscibility gap can be eliminated either by the addition of an ethoxylated alcohol surfactant under conditions that promote the formation of micellar end caps, or by addition of an ionic surfactant that limits the formation of junctions. These changes in morphology have significant impacts on the flow properties of the solutions, and can create structures of potential use in the crystallization of membrane proteins. Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 2 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 2 of 321 Electrokinetic Phenomena and Microfluidics: General Electrokinetics 1 Organizer: Patrick S. Doyle Massachusetts Institute of Technology, Cambridge, MA Organizer: Dimiter N. Petsev University of New Mexico, Albuquerque, NM Presider: Dimiter N. Petsev University of New Mexico, Albuquerque, NM 2. Controlling EOF Using Polymer Coating: An Investigation Using Molecular Dynamics Simulations Gary W. Slater, Owen Hickey and Frйdйric Tessier, University of Ottawa, Ottawa, ON, Canada The suppression of electro-osmotic flow (EOF) through the use of either a polymer brush or a dynamicaly adsorbed polymer coating is widely used in microfluidics, particularly for capillary electrophoresis. In this presentation, I will review the results of our Molecular Dynamics simulations of this problem. For polymer brushes, our data agree with the best available theory; this suggests ways to improve coating. For dynamic coating, our simulation data show that the optimal adsorption strength for the suppression of EOF is around the phase transition for the adsorption of the polymer, a very interesting result which suggests ways to design new coating agents. Finally, we examine block copolymers. 4. Transient Electrokinetic Flow in Cylindrical Microcapillaries Containing a Salt-Free Medium Shih-Hsiang Chang, Far East University, Tainan, Taiwan In general, electrically neutral liquids have a distribution of electrical charges near a surface because of a charged solid surface. This region is well known as the electrical double layer (EDL) and its thickness ranges from a few nanometers up to several hundred nanometers. As the characteristic dimensions of the cylindrical capillary decrease to micro ranges, the electrokinetic effects induced by an EDL between the fluid and charged channel surface are believed to play an important role in studying the heat transfer and flow phenomena. Applications of cylindrical microcapillaries are encountered in biological chips (Biochip) such as micropumps, capillary electrophoretic devices for separation of proteins, and coaxial jet mixing devices used in chemical analysis and biomedical diagnostics. Therefore, an understanding of the electrokinetic transport phenomena in a cylindrical microcapillary is needed for design and operation of microfluid flow in Biochips. Salt-free dispersions comprise a special colloidal system in which the liquid phase contains only counterions dissociated from the surface of the dispersed entities. A typical example in practice includes a dispersion of polyelectrolytes such as DNA, RNA, filamentous actin, microtubules and polyacrylic acid (PAA) in an electrolyte-free liquid medium. Although theoretical studies on the transient electrokinetic flow in a salt-free solution are particularly important for analyzing experimental electrokinetic data for nonaqueous media, which contain essentially no salts, no study has been reported to investigate the transient response of electrokinetic flow in a salt-free solution. Therefore, the main objective of this paper is to derive the exact or accurate analytical solution for the transient electrokinetic flow of a salt-free Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 3 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 3 of 321 medium containing counterions only in cylindrical capillaries. Based on these results, the corresponding transient electrokinetic transport phenomena such as electro-osmosis velocity, electric current, streaming potential, electroviscous effect, and heat transfer coefficient can be obtained in closed form. 5. Control of Nanoscale Flow in Thin Wetting Films by Electric Field Sejong Kim, Jairus Kleinert and Orlin D. Velev, North Carolina State University, Raleigh, NC We report a novel method to manipulate aqueous films of nanoscale thickness by electric field. The ultrathin liquid films with tens of nanometer thickness were formed on hydrophilic mica surfaces under saturation humidity conditions. Applying electric field engendered tangential flow in the film by DC electroosmosis. The direction and speed of the film flow, visualized with fluorescent markers, were readily controlled by the external DC electric field. The film flow rate was characterized as a function of ionic strength, pH of the fluid as well as external electric field. The resulting flow characteristics were consistent with the theory of electroosmosis. To manipulate the flows in a controlled geometry, we confined the flow in 2D Уvirtual wallФ channels by selective hydrophobization with micro-contact printing. This novel 2D nanofluidics methodology will provide a basis for molecular transport and manipulation as well as an enhanced nano scale and molecular level understanding of the interaction of fluids with surfaces. 6. Porous and Microchannel Flow Studies with Improved Spatial and Velocity Resolution Elaine Ulrich, University of Arizona, Tucson, AZ Current studies of micro and nanoflows suffer from limited spatial and velocity resolution due to the diffraction limit for optical techniques and probe size for other anemometry sensors. We describe a force transduction technique that may aid in the direct observation of fluid flows with sub-micron resolution. Of particular interest are flows in the Knudsen regime, where no-slip boundary conditions no longer apply. We investigate modification of Poiseuille flow in small channels in a variety of porous structures and discuss our results. 7. Studies of Bilayers and Vesicle Adsorption to Solid Substrates: Development of a Miniaturized Streaming Potential Apparatus (SPA) Younjin Min, Noshir Pesika, Joeseph A. Zasadzinski and Jacob N. Israelachvili, University of California, Santa Barbara, Santa Barbara, CA A miniaturized streaming potential apparatus (SPA) was newly developed in order to measure surface potentials under different solution conditions while simultaneously visualizing the state of the surfaces such as the adsorption of vesicles or bilayers using fluorescence microscopy or fluorescence recovery after photobleaching (FRAP) technique. Two different sets of substrates (such as Teflon against borosilicate and Teflon) against Teflon under different buffer solution concentrations were used to validate our new design of the SPA. Our results obtained from the SPA show good agreements in both Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 4 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 4 of 321 cases with possible predictions based on a modified Helmholtz-Smoluchowski (H-S) equation. Certain amount of DMPC (1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine) vesicle solutions were introduced into the SPA chamber to investigate how the zeta (ζ)-potential would be changed as the formation of DMPC bilayers on a borosilicate surface. Simultaneous ζ-potential measurements and fluorescence imaging and diffusion coefficients by confocal microscopy using the new SPA allow the monitoring of bilayer formation from vesicles as a function of lipid concentrations. Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 5 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 5 of 321 Environmental Applications and Natural Colloids 1: Colloidal Fate and Transport Organizer: Robert D. Tilton Carnegie Mellon University, Pittsburgh, PA Organizer: Orlando J. Rojas North Carolina State University, Raleigh, NC Presider: Robert D. Tilton Carnegie Mellon University, Pittsburgh, PA Session Overview: This session is dedicated to colloid science in soil and water media. 8. Precipitation of ZnS and HgS: The Effects of Organic Ligands and Humic Substances on Colloidal Stability Boris Lau, Amrika Deonarine and Heileen Hsu-Kim, Duke University, Durham, NC Metal-sulfide (ZnS and HgS) colloids are found in a variety of aquatic systems including mine drainage, anaerobic sediment porewater, municipal wastewater effluent, and hydrothermal vent ecosystems. While occurrence and source information have become available, relatively little is known about the processes that enable the persistence of these metal-sulfides as colloids or nanoparticles. The objective of this study was to identify surface interactions that occur between metal sulfide colloids and dissolved natural organic matter (NOM). We hypothesized that stabilization of ZnS and HgS particles by humic compounds during precipitation depends on specific ligand binding on the metal-sulfide surface as well as bulk structural properties of NOM (e.g., aromaticity, molecular weight, hydrophobicity, reduced sulfur content). Precipitation experiments were conducted with simple, low-molecular weight organic acids that are surrogates for naturally-occurring NOM. Particle size was measured using time-resolved dynamic light scattering. Observed growth rates of ZnS and HgS aggregates varied by orders of magnitude, depending on the type and concentration of organic ligand in solution. Thiol-containing ligands were more effective than hydroxyl-containing ligands for decreasing the growth rates of ZnS and HgS particles. The particles were characterized for elemental composition by X-ray photoelectron spectroscopy. The result of an approximate 1:1 metal to sulfur molar ratio suggested that ZnS and HgS were precipitating in the mixtures. We conducted additional metal-sulfide precipitation experiments with aquatic humic substances isolated from several surface water sources. These humic isolates represent a wide range of chemical properties (e.g., molecular weight, aromaticity, reduced sulfur content). Our preliminary findings indicated that observed growth rates of ZnS and HgS particles decreased by at least one to two orders of magnitude when 0.5-1 mg/L peat humic acid was present. Overall, this study suggests the importance of NOM when evaluating the stability of naturally-occurring and anthropogenic metal-sulfide colloids in natural aquatic systems. 9. The Maximum of Phosphate Adsorption on Alumina Xiao Huang and Gregory D. Foster, George Mason University, Fairfax, VA We conducted a series of phosphate adsorption experiments with alumina and hematite at a range of initial P concentrations and pH values. We found that at low initial P concentrations of < 323 μmole l-1, phosphate adsorption on both alumina and hematite shows a plateau from pH 2.5 to pH 6.5, followed by an abrupt decrease around pH 6.5-7.0. As initial P concentration increases above 500 μmole l-1, the Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 6 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 6 of 321 adsorption on alumina displays a sharp maximum around pH 4.0, while the adsorption on hematite exhibits a steep increase with decreased pH but does not seem to reach a maximum even at pH <3.0. Using surface complexation theory, this study demonstrates that the adsorption maximum on alumina results from (1) phosphate being adsorbed preferentially as protonated complexes at high surface P coverage; (2) the electric potential at the oxide surface approaching a plateau with decreased pH as singly coordinated hydroxyls on Al oxides become fully protonated. Fundamentally, however, the adsorption maximum for alumina at pH 4.0 seems to be related to the absence of proton-active but phosphateinactive triply coordinated hydroxyls at the transformed surface of aluminum oxides. 10. Colloids, Colloids Everywhere: Particle Transport in Streams, Wetlands, Groundwaters, and Soil Waters James Saiers, Tao Cheng, Bin Gao, Yong Huang, Diana Karwan and Shangping Xu, (1)Yale University, New Haven, CT, (2)University of Florida, Gainesville, FL, (3)Texas A&M University, (4)University of Wisconsin Colloid-sized particles, including mineral fragments, plant detritus, and microbes, are ubiquitous in natural waters. The transport of these waterborne particles has important implications to ecological functioning, water quality, and geologic processes. In subsurface environments, particle transport influences the mobility of groundwater contaminants and controls soil-illuviation rates and soil-profile development. Particle transport in surface waters is equally important, affecting the stability of coastal marshes, the formation of landscape features of freshwater wetlands (e.g., tree islands), and nutrient cycling in streams and rivers. We have attempted to advance understanding of these issues by conducting laboratory and field studies intended to elucidate the mechanisms and physiochemical properties that govern the mobility of waterborne particles within natural environments. Our laboratory-based studies have centered on colloid transport and surface reactions within water-saturated and unsaturated sediments. Observations made during pore-scale visualization experiments reveal that colloid mobilization and deposition to air-water and solid-water interfaces is governed by multiple mechanisms, and findings from bench-top column experiments suggest that these mechanisms are sensitive to changes in volumetric moisture content, flow velocity, porewater composition, and colloid size, shape, and mineralogy. Results of other column experiments indicate that colloids mobilized from natural soils are capable of adsorbing and accelerating the transport of radionuclides (cesium and strontium) and herbicides (atrazine) during saturated and unsaturated flow through geologic materials. Our field experiments have been carried out in surface-water environments and have relied on particulate-tracer injections into streams that drain forested watersheds in New England and into surface-water wetlands of the Florida Everglades. Analyses of observations made in the stream-tracer experiments demonstrate that within-stream retention of micrometer-sized particles exhibits a strong seasonal dependence and that, for all seasons, the transport of these microscopic particles differs substantially from that of a conservative tracer. Particle transport within wetlands is complicated by the presence of emergent vegetation. Findings from our tracer experiments in the Everglades demonstrate that vegetation composition affects the advective-dispersive transport of bacteria-sized particles and that emergent plants serve as efficient collectors of these particles. We have used our data Ц from both the laboratory and field experiments Ц to test mathematical models for colloid transport and reaction in soils and in surface water. Although our attempts to simulate the observed phenomena cannot be considered a complete success, our findings Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 7 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 7 of 321 suggest that suitable theoretical frameworks for particle transport in surface and subsurface environments are tractable. 11. The Effect of Air and Water Phase Configuration on Colloid Retention in Partially Saturated Porous Media Yuniati Zevi, Yan Jin, Masa Prodanovic and Steven L. Bryant, (1)University of Delaware, Newark, DE, (2)University of Texas at Austin, Austin, TX In a partially saturated system the accumulation of colloid at interfaces such as air-water (AW), solidwater (SW) and air-water-solid (AWS) interfaces depend on the area of those interfaces and its accessibility to the water phase. Accumulations of colloids near the three-phase contact line (AWS) depend on the water volume associated with that line. The area of interfaces and contact line can be varied independently by adjusting the capillary pressure (or moisture content) and/or contact angle. In the present study, we keep the contact angle constant and vary only capillary pressure to vary interface configurations and areas of AW and AWS interfaces. Experiments are being conducted using 3D porescale micromodels, made from rectangular capillary tube with inner dimension of 100 μm by 1000 μm, packed with glass beads which have average diameter of 75 μm, and with fluorescent latex microspheres with diameter of 1 μm. Both capillary tube and glass beads were treated with acid to achieve uniform hydrophilic surface. Using a fast laser scanning microscope, volumetric (3D) images are collected in near real time during dynamic flow conditions as well as static conditions. The images will allow for investigation of the air and water phase configurations and its effect on colloid retention at the interfaces. An advanced confocal software Volocity is used for particle tracking and image analysis to quantify the number of particles retained for specified areas. Modeling involves Progressive Quasi-static Algorithm implementation of level set method to predict the configuration of fluids in porous media by varying the pore space geometry (square and equilateral triangles sphere-sphere configurations) and interfacial (capillary) pressure. Results from the micromodel experiments will be used to validate the model. 12. Effect of Wetting and Drying Cycles on Autochthonous Soil Colloid Mobilization Eric Michel, Samer Majdalani, Liliana Di Pietro and Rafael Angulo-Jaramillo, (1)National Institute for Agricultural Research, (INRA), Avignon, France, (2)LTHE, Grenoble, France, (3)ENTPE and LTHE, Lyon and Grenoble, France Understanding colloid mobilization and transport in soils is a major concern for environmental protection and water resources management: They can act as vectors for sorbing pollutants, transporting them farther and faster through the vadose zone towards the water table than pollutants simply dissolved in water. Additionally, the existence of preferential flow paths in the soil such as cracks or invertebrate burrows is known to lead to an even faster breakthrough of the colloids. Some column or field scale undisturbed soil studies have identified the factors favouring/disfavouring particle mobilization, such as ionic strength, pH, initial soil moisture, trapping at air water interfaces or rainfall intensity. It appears however that one potentially important factor has been overlooked: the influence of the irrigation pattern undergone during the soil history. As a first step toward the study of this parameter, we carried out a series of infiltrationdrainage experiments to investigate systematically the effects of periods without rain (pauses) on autochtonous particle mobilization in undisturbed soil columns. We showed that pause duration effect on Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 8 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 8 of 321 mobilization is significant: the cumulative mass of particles eluted with the first 120ml of effluent is fifteen times higher when pause duration lasts 200 hours than when it lasts 1 hour. This variation occurs mainly during the transient stage of the flow (see figure). We found that this behavior is correlated with soil mean water content and proposed a mobilization mechanisms based on our observations. In a second experimental step we compare pause duration and ionic strength effects in term of mobilization efficiency. For this purpose we performed a new series of infiltration drainage-experiments keeping the pause duration constant, but changing the ionic strength of infiltration water from 10-5 to 10-1 M. We will discuss the outcome of this comparison, and highlight the practical impacts of our findings on an engineering and policy making point of view. 13. Effect of Hydrodynamics on Colloid Retention in Unsaturated Pore-Scale Experiments Volha Lazouskaya, Xiaoyan Shi, Lian-Ping Wang and Yan Jin, University of Delaware, Newark, DE Understanding colloid transport in soil is important for the ability to predict colloid and colloid-associated transport of contaminants and to protect soil and groundwater resources. Unsaturated porous media often serves as a representation of unsaturated soil thus providing a more general understanding of colloid retention mechanisms. While sample-scale (column) experiments provide the key data in colloid transport, pore-scale experiments involving various imaging techniques have become an additional valuable source of information. In unsaturated porous media, colloids can be potentially retained at solidwater interface (SWI), air-water interface (AWI), and contact line. In particular, the retention at AWI and contact line is in general poorly understood. While the solution chemistry parameters such as pH and ionic strength and surface properties of colloids and porous media have been extensively investigated, more recent studies suggest the importance of hydrodynamics in colloid retention. The first part of the present study is a pore-scale experimental investigation of colloid retention employing a microfluidic channel and a confocal microscope. The micromodel visualization focuses on colloid behavior in the interfacial region (AWI and contact line) under dynamic conditions, with different interface velocities of both advancing and receding interfaces. Hydrodynamic conditions have been shown to affect colloid retention at AWI and contact line by affecting colloid availability for the retention as well as affecting the efficiency of colloid interfacial interactions. Relative preference of AWI and contact line for colloid retention has been analyzed. The second part is the development of a computational approach to simulate the viscous flow and colloid transport near the AWI and moving contact line. A mesoscopic multiphase lattice Boltzmann method and a Navier-Stokes based volume-of-fluid method are applied simultaneously to simulate the interfacial flow. The trajectories of colloids are then integrated numerically by solving the colloid's equation of motion, under the influence of physicochemical, hydrodynamic, capillary, Brownian and body forces and torques. Results from the computational approach will be compared to the micromodel observations, including the shape of the air-water interface and distribution of colloids near AWI and contact line. Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 9 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 9 of 321 General Papers in Colloid Science 1: Interactions Organizer: Michael A. Bevan Johns Hopkins University, Baltimore, MD Organizer: Joelle Frechette Johns Hopkins University, Baltimore, MD Presider: Joelle Frechette Johns Hopkins University, Baltimore, MD 14. Experimental Comparison of Particle Interaction Measurement Techniques Using Optical Traps Timothy P. Koehler, Ryan A. Molecke, Christopher M. Brotherton and Anne M. Grillet, (1)Sandia National Laboratories, Albuquerque, NM, (2)University of New Mexico, Albuquerque, NM Optical tweezers has become a powerful and common tool for sensitive determination of electrostatic interactions between colloidal particles. Recently, two techniques, УblinkingФ tweezers and direct force measurements, have become increasingly prevalent in investigations of inter-particle potentials. The УblinkingФ tweezers method acquires physical statistics of particle trajectories to determine drift velocities, diffusion coefficients, and ultimately colloidal forces as a function of the center-center separation of two particles. Direct force measurements monitor the position of a particle relative to the center of an optical trap as the separation distance between two continuously trapped particles is gradually decreased. As the particles near each other, the displacement from the trap center for each particle increases proportional to the inter-particle force. Although commonly employed in the investigation of interactions of colloidal particles, there exists no direct comparison of these experimental methods in the literature. In this study, an experimental apparatus was developed capable of performing both methods and is used to quantify electrostatic potentials between particles in several particle/solvent systems. Comparisons are drawn between the experiments conducted using the two measurement techniques, theory, and existing literature. 15. On the Depletion Effect in Colloids: A New Correlation Effect in Brownian Motion Peter Kotelenez, Marshall J. Leitman and J. Adin Mann Jr., Case Western Reserve University, Cleveland, OH Our object is to formulate and analyze a physically plausible and mathematically sound model to better understand the phenomenon of clustering in colloids. Here, the term depletion force refers to a force which is associated with clustering due to depletion of small molecules in the region between large particles. Our model is stochastic leading to a correlation effect but derived from a deterministic formulation in a Newtonian setting. A mathematical transition from the deterministic dynamics of several large particles and infinitely many small particles to a kinetic description of the stochastic motion of the large particles is available in the published work of Kotelenez and is key to our result. Assume that the velocity distribution of the small particles is governed by a probability density, which is reasonable, then the mean-field force on the large particles can be represented as the negative gradient of a scaled version of that density. The stochastic motion of the large particles can then be described by a system of correlated Brownian motions. The scaling in the transition preserves a small parameter, the correlation length. From the limiting kinetic, stochastic equations we compute the probability flux rates for the separation between two large particles. We show that, for short times, two particles sufficiently close Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 10 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 10 of 321 together tend to be attracted to each other. This agrees with the depletion phenomena observed in colloids. To quantify this effect, we extend the notion of Van Kampen's one-dimensional probability flux rate in an appropriate way to account for higher dimensional effects. 16. Computational Study of Colloidal Dynamics in Entropic Force Fields Bryce D. Sturtevant and David S. Corti, Purdue University, West Lafayette, IN The ability of colloidal particles to self-organize suggests that colloidal particles could be used as precursors for advanced materials via the generation of complex microstructures. The precise control of colloidal dispersions rests upon our knowledge of the forces that arise between particles and surfaces of various shapes. An important class of inter-particle forces is induced by the presence of other colloidal species and arises solely as a result of entropic considerations. These entropic forces can promote orderdisorder transitions in the dispersion microstructure and may be responsible for a disorder-disorder transition. Furthermore, passive structures etched into the walls of the container can create entropic force fields of sufficient range and magnitude so that the motion and position of large colloids can be controlled, thereby generating various two-dimensional fluid-like and solid-like phases on chosen templates. By providing new and potentially simple routes for the directed self-assembly of novel mesoscopic structures, the use of entropic force fields to create various complex microstructures is a promising approach to the production of advanced materials. Various issues concerning the feasibility of such methods, however, need to be addressed. For example, the dynamics of colloidal particles diffusing through an entropic force field is not well known. Since the entropic forces that arise within colloidal dispersions become repulsive at intermediate separations, large repulsive barriers may kinetically stabilize suspensions even though coagulation/deposition is thermodynamically favored. In some instances, these repulsive barriers may prevent the desired deposition or coagulation. We investigate in detail the dynamics of hard-sphere colloids moving above and onto surfaces of various shapes via the use of two computational methods: molecular dynamics (MD) and stochastic rotation dynamics (SRD). SRD, which is a method for coarse-graining fluid interactions while still including the correct hydrodynamic interactions, such as the important lubrication forces, allows us to determine the relative influence of hydrodynamic and entropic effects on particle deposition. We find good agreement between our calculated and previously measured (via experiments) normal and transverse diffusion coefficients of a colloid particle located near a hard wall. A comparison of MD and SRD results also reveals that SRD captures interesting solvent behavior when the gap distance between colloids or between colloids and surfaces become quite small. While no simulation method is optimal for all systems of interest, our studies indicate that SRD is a robust computational tool that should be applicable to a reasonable variety of other technologically relevant colloidal dispersions. 17. The Generalized Inversion of Reflection Interference Contrast Microscopy J. Clemente Contreras and James A. Silas, Texas A&M University, College Station, TX Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 11 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 11 of 321 Reflection interference contrast microscopy (RICM) is a microinterferometric technique that is used to study particle and vesicle interactions with surfaces. An image formed by RICM contains precise information about the topography of the object under observation; however, current use focuses on comparison of interference patterns to patterns from known geometries and sizes. As our work primarily uses deformable objects, we seek to relax the assumptions about the geometry of the reflecting surface and develop a Generalized Inverse RICM procedure. Generalized Inverse RICM uses non-planar image formation theory within a regularization procedure to reconstruct the local geometry of a reflecting surface in systems with either single reflecting layers (particles) or double reflecting layers (vesicles). The resulting procedures yield the location of a particle in three dimensions as well as a direct measurement of particle shape near a surface. 18. Adsorbed Polymer-Surfactant Layer Structure Probed Using Atomic Force Microscopy Emily E. Meyer, Nick J. Ainger, Neil S. Shaw and Raymond R. Dagastine, (1)The University of Melbourne, Parkville, VIC 3056, Australia, (2)Unilever Research, Port Sunlight, United Kingdom The remarkable number of behaviors of polymer-surfactant complexes has lead to their use in a wide range of applications in personal care products, food formulations and pharmaceuticals. There has been considerable study of oppositely charged polymer-surfactant complexes in solution and, more recently, the behavior of such complexes and their components on surfaces have also been considered. However, little attention has been given to the dynamics process by which the interaction forces between adsorbed layers transition from repulsive forces to attractive forces with bulk concentration changes. In this work we use atomic force microscope (AFM) to investigate the properties of adsorbed polymer-surfactant complexes using anionic surfactants and cationic polyelectrolytes. Force vs separation data obtained with the AFM allow one to determine the adhesive properties of the system, conformational changes within the layer, and the dynamics of how these changes are occurring as a function of bulk surfactant and electrolyte concentrations. Force spectroscopy was also employed to probe polymer conformational changes and adhesion behavior. 19. Nanoparticle Interactions in Slit Pores Shannon L. Eichmann, Texas A&M University, College Station, TX and Michael A. Bevan, Johns Hopkins University, Baltimore, MD This talk will present measurements of interactions between nanoparticles and confining surfaces with and without adsorbed polyelectrolytes and proteins. Specifically, results will be presented for evanescent wave scattering and video microscopy measurements of 50, 100, and 250nm gold nanoparticles confined in submicron gaps between parallel walls. Initially, measurements were performed for bare nanoparticles stabilized via long range electrostatic repulsion in low ionic strength media. After establishing the behavior of bare particles at low ionic strengths, measurements were performed for particles stabilized by adsorbed polyelectrolyte multilayers and proteins at physiological ionic strengths. Polyelectrolyte layers were adsorbed in a layer-by-layer fashion on the particle and confining surfaces to control layer thicknesses and the range of macromolecular repulsion within several nanometers. In contrast, bovine serum albumin was adsorbed to give adsorbed monolayers with a uniform range of repulsion. Equilibrium Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 12 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 12 of 321 analyses of single and ensemble particle height distributions normal to the confining walls produce electrostatic and macromolecular potentials in excellent agreement with theoretical predictions. These results demonstrate a consistent interpretation of nanoparticle interactions in confined geometries. Ongoing work is extending the methods presented here to measure specific interactions between biomacromolecules attached and oriented to nanoparticle and wall surfaces. 20. Measuring Forces and Torques Between Anisotropic Colloidal Particles Jason W. Merrill, Sunil K. Sainis and Eric R. Dufresne, Yale University, New Haven, CT We present a novel method for extracting the hydrodynamic and electrostatic interactions of anisotropic colloidal particles. By measuring the correlated diffusion and drift of interacting clusters of particles, we can experimentally measure the mobility tensor and forces/torques on each particle. We apply this method to measure the electrostatic interactions of anisotropic particles in the limit where screening length is much larger than the particle size---relevant to microparticles in nonpolar solvents and nano/bio colloids in water. We find dramatic departures from the predictions of Debye-Huckel theory. Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 13 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 13 of 321 Life Science Applications 1: Polymers Organizer: Norma Alcantar University of South Florida, Tampa, FL Organizer: Raymond S. Tu The City College of The City University of New York, New York, NY Presider: Ryan Toomey University of South Florida, Tampa, FL 21. Polyelectrolyte Multilayer Films Ц a General Approach to Biofunctional Coatings Gero Decher, Institut Charles Sadron, Strasbourg, France Layer-by-layer (LBL) assembly is an easy to use method for the fabrication of multicomposite films and has kindled widespread interest in such nanohybrids. Electrostatic interactions between anionic and cationic compounds (e. g. synthetic or natural polyions such as polyelectrolytes, DNA, proteins or even colloids) offer five major advantages: • Layer-by-layer construction due to surface charge reversal in each layer • Restriction to single layers due to repulsion between last layer and excess material in each deposition cycle • Low steric demand for interaction between oppositely charged ions • Deposition on almost any solvent accessible surface • Easy access to (bio)functional multicomposite films Since the technique allows interfacing a wide variety of (bio) materials with predefined spatial arrangement, it has successfully been introduced to both materials science and applied bio-sciences. This presentation will start with simple examples of LBL-film containing e.g. proteins and extend to films in which the composition of the film controls the interaction with cells. It will finish with the construction of multilayers containing cells and with devices for biomedical use. For more information see for example : Polyelectrolyte Multilayer Films Ц A General Approach to (Bio)Functional Coatings, N. Jessel, P. Lavalle, V. Ball, J. Ogier, B. Senger, C. Picart, P. Schaaf, J.-C. Voegel and G. Decher in Macromolecular Engineering Vol. 2, УElements of Macromolecular Structural ControlФ (Y. Gnanou, L. Leibler and K. Matyiaszewski, Eds.), Wiley-VCH: Weinheim, 2007, 12491306. 22. Impedance Characteristics of Conducting Polymer Films J. Faye Rubinson, Yohani Kayinamura and Marc Ovadia, (1)Georgetown University, Washington, DC, (2)University of Illinois, Chicago, Chicago, IL A semiconductor|electrolyte interface is normally characterized by double layer capacitance leading to reactive impedance. This characterisitic is undesirable for bioelectrode design. Since uncompensated charge exists only at the surface in steady-state for conductors, sensing is detrimentally affected, as the reactive impedance creates a high-pass filter intrinsic to series reactances. For this reason, the Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 14 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 14 of 321 achievement of an Ohmic interface would be highly desirable. In our laboratory, we have achieve near Ohmic behavior for electrodes in vitro within a broad frequency range when modified with PEDOT film. We have suggested that ohmic behavior is primarily due to the identity of counterion, homogeneity and low porosity of the film. Using Electrochemical Impedance Spectroscopy and Raman Spectroscopy, we have conducted a comparative study of PEDOT and PEDOP based on their chemical identity and we found that the heteroatom may be playing a role in observed ohmic behavior for PEDOT by contributing to the formation of specific chemical states that affect the uncompensated charge at the surface. Results will be reported and discussed for PEDOT and PEDOP, as well as results obtained with another conducting polymer, carbazole. 23. Synthesis of PEO-PCL-PEO Triblock Copolymers for Cosmeceutical Application In Woo Cheong, Heui Kyoung Cho, Jin Hun Cho and Jung Hyun Kim, (1)Kyungpook National University, Daegu, South Korea, (2)Yonsei University, Seoul, South Korea A series of poly(ethylene glycol)-block-poly(ε-caprolactone)-block-poly(ethylene glycol) (PEO-PCLPEO) triblock copolymers were prepared and then used for the investigation of the effects of the ratio of ε-caprolactone to poly(ethylene glycol) (i.e., [CL]/[EO]) on the physical properties and release behavior of microand nano-capsules of vitamin derivatives. As model drugs, retinol and ascorbic acid-2-glucoside were used. For release behavior and proliferation of skin cell, artificial skin (Neoderm(R)) and hairless mouse were studied. In order to elucidate the role of PEO-PCL-PEO triblock copolymers during the drug permeation into skin layer, fluorecein isothiocyanate (FITC) was conjugated to the copolymers and monitored by using confocal laser scanning microscopy. The effects of [CL]/[EO] on the physical properties and release behavior of O/W (or W/O/W) emulsions will be discussed. [Figure Description] (a) Plot for the number of epidermis cell layers vs. PEO-PCL-PEO triblock copolymers. Optical microscope images of the cross-sectional view of the artificial skin cultivated with retinol emulsion for 2 weeks: (b) control (without retinol treatment), (c) with 1 wt.% of P-222, (d) with 1 wt.% of P-232, (e) with 1 wt.% of P-242, (f) with 1 wt.% of P-252, (g) with 3 wt.% of P-222, (h) with 3 wt.% of P-232, (i) with 3 wt.% of P242, and (j) with 3 wt.% of P-252. n indicates the number of epidermis cell layers. Stratum corneum was separated from the epidermis layer while microtoming. (This work was supported by MOCIE, NGNT No. 10024160) 24. Thermoresponsive Biocompatible Chemically Degradable Triblock Copolymer Hydrogels Peter Jeppe Madsen, Steven Peter Armes, Andrew Lewis, Karima Bertal and Sheila MacNeil, (1)University of Sheffield, Sheffield, United Kingdom, (2)Biocompatibles UK Ltd., Farnham, United Kingdom The synthesis of novel thermo-responsive ABA triblock copolymers in which the outer A blocks comprise poly(2-hydroxypropyl methacrylate) and the central B block is poly(2-(methacryloyloxy)ethyl phosphorylcholine) is achieved using atom transfer radical polymerization. These novel triblock copolymers form thermo-reversible, free-standing physical gels with critical gelation temperatures and mechanical properties that are highly dependent on the copolymer composition and concentration. TEM studies on dried dilute copolymer solutions indicate the presence of colloidal aggregates, which is Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 15 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 15 of 321 consistent with micellar gel structures. This hypothesis is consistent with the observation that incorporating a central disulfide bond within the B block leads to thermo-responsive gels that can be efficiently degraded using mild reductants such as dithiothreitol (DTT) over time scales of minutes at 37 ∞C. Moreover, the rate of gel dissolution increases at higher DTT/disulfide molar ratios. Finally, the resulting gels have been shown to be highly biocompatible towards cell monolayers: only a modest reduction in cell proliferation was observed with little, if any, evidence for cytotoxicity. These gels had practically no deleterious effects when used in combination with 3D reconstructed skin models and may have potential applications as wound dressings. 25. Multivariant Polymer Brushes a NEW Platform for Understanding Surface-Protein Interactions Shafi M. Arifuzzaman and Jan Genzer, North Carolina State University, Raleigh, NC The adsorption of proteins from a solution to solid surfaces is one of the most extensively studied topics due to its significant scientific interests and widespread applications. On the one hand, uncontrolled adsorption of proteins on an implant surface, such as catheters, stents, or pacemakers, can result in encapsulation and ultimate deterioration of the device or surface-induced thrombosis. On the other hand, to realize commercial success in tissue-engineered products there must be precise tuning of protein and cell adhesion to the synthetic scaffolds. Surface-bound polymer gradients provide a novel platform for systematically evaluating the parameters affecting protein adsorption on man-made surfaces. We chose to use poly(2-hydroxylethyl methacrylate) (PHEMA) brushes in our study due to its ease of synthesis on surfaces at high grafting density by controlled radical polymerization. Moreover, it offers a rather broad range of chain length and/or grafting density that can be varied to manipulate protein adsorption. Additionally, it is possible to attach molecules with different functionality to PHEMA via its hydroxyl groups. This chemical tailoring will help PHEMA surfaces satisfy the growing demands of many complex biomedical applications. We employed a linear gradient in MW of grafted PHEMA and silane coupling agents to modify the OH groups in our study. It has been well known for decades that alkylchlorosilanes in solution react with hydroxylated surface to produce a surface modified by SAMs. The end-functionality of adsorbed organosilane subsequently dictates the functionality of the surface. In our experiments we used fluorine-containing organosilane coupling agents 1H,1H,2H,2H perfluorodecyldimethyl-chlorosilane (mF8H2) and 1H,1H,2H,2Hperfluoro-decyltrichlorosilane (tF8H2) and optimized solvent conditions for silane attachment. The substrates were characterized by a battery of analytical tools, including, ellipsometry for thickness measurement, contact angle goniometer for surface energy estimation, near-edge x-ray absorption fine structure (NEXAFS) spectroscopy for the identification of chemical bonds and determination of their relative population density within the sample, and a relative measurement of the concentration of the F8H2 groups on the substrate and their possible orientation. Our experimental results indicate that the highest amount of fluorinated material on the PHEMA polymer brush occurs when the deposition is done in cyclohexhene with dibutyl dilauryl tin as a catalyst. These results open up a new venue in preparing novel materials with varying functionality using silane coupling agents. By utilizing these systems we can systematically vary the surface property of polymer brush and study their effect on protein adsorption. Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 16 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 16 of 321 26. Monodispersed Biocompatible Thermally Responsive Nanoparticle Hydrogels Thuy T. Chastek, Thomas Q. Chastek, Aniket Wadajkar, Kytai Nguyen and Steven D. Hudson, (1)NIST, Gaithersburg, MD, (2)Universtiy of Texas-Arlington, Arlington, TX Over the last decade, hydrophilic polymer gels of nanoscale size (nanogels) have been extensively investigated due to their many potential applications including biosensors and drug delivery systems. Their ability to swell in suitable hydrophilic solvents to trap numerous substances inside the gel makes them attractive for use in delivery applications such as protein and gene delivery. Particular focus has been directed toward УsmartФ hydrogels which swell or shrink rapidly in response to external environmental stimuli such as pH, temperature, ionic strength, and electro stimulus. We synthesize such monodisperse biocompatible thermally responsive nanoparticle poly(N-isopropylacrylamide) hydrogels, and analyze their size with dynamic light scattering (DLS) and electron microscopies. We also synthesize these monodisperse nanoparticles within microfluidic devices having integrated measurement capabilities (on-line dynamic light scattering) that we have developed. These nanoparticles were synthesized by varying the concentrations of N-isopropylacrylamide monomer, biocompatible surfactants (Pluronics L64, P65, and P85), and potassium persulfate initiator. Monodisperse nanoparticles were obtained with optimal conditions. The surfactant and initiator concentration significantly affect the resulting particle size. The 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt) (MTS) colorimetric assay showed these nanoparticles are biocompatible. Abstract Book The 82 ACS Colloid and Surface Science Symposium Page 17 of 321Book The 82 ACS Colloid and Surface Science Symposium Page 17 of 321 Nanoscale Synthesis 1: Metals Organizer: Hong Yang University of Rochester, Rochester, NY Organizer: Ilona Kretzschmar City College of City University of New York, New York, NY Presider: Raymond E. Schaak Pennsylvania State University, University Park, PA 27. Controlling the Shapes of Colloidal Nanocrystals Younan Xia, Washington University, St. Louis, MO Controlling the nanocrystal shape may initially seem like a scientific curiosity, but its goal goes far beyond aesthetic appeal. For metal nanocrystals, shape not only determines their intrinsic chemical, plasmonic, and catalytic properties but also their relevance for electronic, optical, and sensing applications. Part of my research in the last five years has focused on shape-controlled synthesis of noble metal nanocrystals. While the synthetic methodology mainly involves solution-phase redox chemistry, we have been working diligently to understand the complex physics behind the simple chemistry Ц that is, the nucleation and growth mechanism leading to the formation of nanocrystals with a specific shape. Polyol synthesis of silver nanocrystals provides a good example to illustrate this concept. We discovered that the shape of a nanocrystal are dictated by both the crystallinity and shape of nanocrystallite seeds, which are, in turn, controlled by factors such as reduction rate, oxidative etching, and surface capping. The same mechanism also works for other systems including gold, palladium, and platinum. The success of these syntheses has enabled us to tailor the electronic, plasmonic, and catalytic properties of noble metal nanocrystals. 28. Single Nanocrystal Spectroscopy Paul Mulvaney, The University of Melbourne, Parkville, Australia We focus on the possibility to study the optical properties of single metal particles using dark-field microscopy. It is now possible to routinely collect the scattered light from single metal nanocrystals and use this to study the effects of particle size and shape on the surface plasmon (SP) resonances. We show that the linewidth and energy of the SP resonance is acutely sensitive to the particle end cap geometry, to the aspect ratio and to atomic roughness on the particle surface. We map the surface plasmon resonance landscape for six different crystal morphologies of gold nanocrystals.