Oral Presentation Abstracts

Talks 251 through 300

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251

Rate and Nature of Reactions Between Hematite and Fe(II)

Byong-Hun Jeon, Brian A. Dempsey, William D. Burgos, Richard A. Royer, Je-Hun Jang , Civil and Environmental Engineering, 212 Sackett, Penn State University, University Park, PA 16802

The reaction of Fe(II) with hematite was studied under strict anoxic conditions. An initial rapid removal of Fe(II) by adsorption was followed by a much slower rate of removal, and equilibrium was not established within 30 days. In spite of verified controls over O2 and light irradiation, there was incomplete recovery of total Fe(II) by 20-hr 0.5 N HCl extraction. The residual Fe(II) was substantially recovered using 3 N HCl extraction, which is an operational indicator for magnetite. Magnetite is stable relative to hematite for some of the experimental conditions (pH greater than 5.8 and for Fe(II) concentrations in the range of 10-4 M.). However, a portion of total Fe(II) was not recovered by 0.5 N HCl at pH greater than 4.0 in the presence of sulfate. The formation of non-hematite phases is under investigation using adsorbate that is enriched in 57Fe followed by 57Fe-Mössbauer spectroscopy. The same experiments will be interpreted using operational extractions followed by ICP-MS for Fe isotopic ratios.


252

Adsorption and Regeneration of Phenol and Phenolic Dimers on Graphite

Aluisio Pimenta, James Kilduff , Rensselaer Polytechnic Institute, 110 8th St./5049 JEC Building, Troy, NY 12180

We have conducted a series of experiments designed to probe the mechanisms for irreversible sorption of phenol by carbon surfaces. The production of phenolic multimers from phenol in the presence of graphite was measured, providing strong evidence of a surface-catalyzed oxidative coupling reaction. Strong physisorption of phenolic multimers has been proposed as one explanation for irreversible adsorption of phenol on carbon surfaces such as activated carbon. To evaluate this hypothesis, we measured the adsorption of phenol and two phenolic dimers, 2,2'- and 4,4'-dihydroxybiphenyl, in single and bi-solute systems, by graphite, and measured subsequent regeneration by methanol. Graphite was chosen as a model non-porous surface, representative of carbons used in water treatment, and black carbon materials found in the environment. Adsorption of phenol and phenolic dimers followed the Langmuir model at low pH, but deviations were detected at high pH due to the predominance of irreversible adsorption. Sorption of the dimers was stronger than phenol, as expected. However, dimer regeneration by methanol extraction was as efficient as for phenol. Therefore, the observed irreversible adsorption of phenol cannot be explained by a mechanism involving phenol sorption, followed by reaction, to produce irreversibly physisorbed reaction products. Competitive adsorption experiments were conducted at low and high pH. These, and other experiments probing the irreversible adsorption of phenol will be discussed.


253

The Effect of Interfacial Films on Mass Transfer of Benzene and Naphthalene from Petroleum Oils to Water

Catherine Pasion and Subhasis Ghoshal, Department of Civil Engineering, McGill University, 817 Sherbrooke Street West, Montreal, QC H3A 2K6, Canada

At contaminated sites, petroleum oils often remain in contact with ground or surface water for long periods of time before or during any attempted remediation. During that time solutes such as benzene or polycyclic aromatic hydrocarbon compounds are continuously released from the oil phase into aqueous phase causing ground and/or surface water contamination. Extended contact of oil and aqueous phases (aging) results in several unique interfacial phenomena, one of which is the formation of semi-rigid films at the oil-water interface for oils that contain asphaltene or resin fractions. The objective of the research was to investigate if aging results in retarded rates of dissolution of aromatic compound solutes from petroleum phases. The equilibrium partitioning and mass transfer rates of benzene and naphthalene in several oil-water systems were evaluated in laboratory experiments over aging periods ranging up to 35 days. The research demonstrated that with aging the mass transfer rate coefficients of the target solutes from: (i) Brent Blend crude oil to water was reduced by up to a factor of 4; (ii) the mass transfer rate coefficient of solutes from gasoline amended with asphaltenes and/or resins decreased by a factor of 2.3 to 66.


254

Influence of Surface Charge Nanoheterogeneity on the Attachment of Colloidal Particles to Solid Surfaces in a Stagnation Point Flow System

Jeffrey Y. Chen, Subir Bhattacharjee, and Menachem Elimelech, Yale University, PO Box 208286, New Haven, CT 06520-8286

The deposition kinetics of polystyrene latex particles onto glass surfaces with patchwise surface charge nanoheterogeneity were investigated. Surface charge nanoheterogeneity was micropatterned onto glass surfaces by silanizing well-controlled fractions of the glass surface using a soft lithographic technique. The micropatterns of silanized surfaces were fabricated by micromolding in capillaries with an elastomeric mold with patterned relief surface structure, a soft lithographic technique. The silanized patterns acquired a positive charge on an otherwise negatively charged native glass surface. A broad spectrum of charge nanoheterogeneity feature sizes was considered, ranging from patches much smaller than the particle size to those much larger than the particle size. Atomic force microscopy was employed to characterize the charge heterogeneity created on the glass surfaces. A stagnation point flow setup was then used to directly observe the deposition of spherical colloidal particles onto the patterned glass surfaces. The observed experimental particle deposition rates onto the heterogeneous glass surface under different physico-chemical conditions were compared to predictions of a simple patchwise charge-heterogeneity model. Furthermore, the patterns formed by preferential deposition of particles onto oppositely charged patches revealed a pronounced influence of the patch size and distribution on the particle deposition process.


255

Colloidal Aggregate Structures and the Filtration of Sediment Beds

Simon Biggs, Chemistry Dept., Sharna Glover, and Yaode Yan, Chemical Engineering Dept., The University of Newcastle, University Drive, Callaghan, NSW 2308 Australia

The flocculation of colloidal particles for solid-liquid separation is routinely used in many industries including mineral processing, water treatment and paper making. Despite this, surprisingly little is known about how to obtain the optimum aggregate properties to achieve desired results in the sedimentation and filtration steps. In this study, we have been investigating the aggregation of alumina colloids using poly(acrylic acid). The aggregation stage is probed using light scattering, turbidity and back scattering data. Aggregate structure evolution is obtained from fractal analysis of sedimentation or light scattering data. Aggregate properties have been determined as a function of flocculant type and concentration as well as in terms of the mixing conditions. Compressive yield stresses and filtration data have also been obtained as a function of the aggregate properties (size and fractal dimension). The importance of controlling flocculation to obtain desired filtration properties will be highlighted in this presentation. Methods to control aggregate properties through a control of the aggregation mechanism will also be discussed.


256

Charging Behavior of Surfactant Stabilized Polystyrene Latexes

Jan Sefcik, Giuseppe Storti and Massimo Morbidelli, Swiss Federal Institute of Technology (ETH), Department of Chemical Engineering, Universitatstr. 6, CH-8092, Switzerland

Surfactant stabilized polystyrene latexes were studied under both stable and aggregating conditions. Their characterization included determination of a surfactant adsorption isotherm and electrophoretic mobility as a function of the surfactant coverage and the solution ionic strength. These measurements indicated that, in the range of ionic strength values investigated, the surface charge of primary particles is constant during salt induced destabilization of the latex for a given surfactant coverage. Rate constants of doublet formation were carefully measured in slowly aggregating latexes for a range of conditions and surface potentials of primary particles were calculated using appriopriate theories for both constant charge and constant potential limiting regimes. Care was taken to account for the correct limiting behavior of double-layer repulsion at the zero separation between the two particles. In both constant charge and constant potential cases we obtained qualitatively the same behavior for the degree of surfactant counterion binding. It was found to be only weakly dependent on the ionic strength, while it was mainly governed by the surfactant coverage and it varied between 0.3 and 0.8 with increasing surfactant coverage for the latexes examined.


257

Phase Transitions, Interfacial Tension, and Turbidity of Colloid-Polymer Systems

Marc Robert, Rice Quantum Institute, Center of Nanoscale Science and Technology, and Department of Chemical Engineering, Bing-Hung Chen, Jiun-Ting Lee, Behnaz Payandeh, Department of Chemical Engineering, Rice University, 6100 S. Main, Houston, TX. 77005, USA

Phase transitions of systems consisting of colloidal particles and nonadsorbing polymer in a solvent are studied theoretically in two dimensions. The colloids are modeled as hard spheres and the polymer as an ideal gas. For a monodisperse polymer, liquid-liquid separation is predicted to occur for appropriate colloid concentrations when the ratio s of the radius of gyration of the polymer to the radius of the colloidal particle is greater than 0.31. Polydispersity of polymer is found to increase the extent of liquid-liquid coexistence, and when the average s is smaller than 0.31, and for appropriate colloid concentrations, liquid-liquid coexistence occurs provided the polymer size distribution is broad enough. Next, the order parameter and interfacial tension of a colloid-polymer system consisting of grafted silica particles in cyclohexane in the presence of the soluble polymer polydimethylsiloxane are determined experimentally in the entire liquid-liquid coexistence region, from the liquid-solid boundary to the critical point. The renormalized critical exponents of the order parameter and interfacial tension are found to be, respectively, b*=0.371+0.026 and m*=1.30+0.08, and are discussed in the light of theoretical predictions. The osmotic compressibility and the correlation length of this colloid-polymer system are determined by turbidity measurements in the entire one-phase liquid region. The normalized critical exponents of the osmotic compressibility and the correlation length are found to be respectively g*=1.39+0.01, and n*=0.71+ 0.01, while the amplitude of the correlation length is 16.0 + 0.3 nm. Comparison is made with theoretical predictions.


258

Semiflexible Polyelectrolytes

K. Ghosh, Department of Physics, G.A. Carri and M. Muthukumar, Department of Polymer Science and Engineering, University of Massachusetts, Amherst MA 01003

Using a variational calculation, we have considered the effect of chain length, intrinsic backbone stiffness, solvent quality and salt concentration on the size and structure of a single semiflexible polyelectrolyte in dilute solution. Explicitly, we have calculated the radius of gyration (R g) and effective persistence length for different solvent qualities and salt concentrations. A thorough analysis of the crossover behavior and the results regarding the structure of a single chain will be presented. We also investigated the many chain problem and at the mean field level calculated Isotropic to Nematic transition concentration and the orientational order parameter as a function of chain stiffness and salt concentration. The phase diagram for the system has also been calculated under different conditions.


259

Simulations of Polyelectrolytes

Mark J. Stevens, Sandia National Laboratories, P.O. Box 5800 MS 1111, Albuquerque, NM 87185-1111

Polyelectrolyte systems offer a rich variety of phenomena some of which has been unresolved for many years. For example, condensation of DNA into toroidal structures is not completely understood. More generally, the nature of interactions between like-charged macroions, particularly the possibility of attractive interactions, is unsettled. Using a simple coarse-grained model of DNA, molecular dynamics simulations reveal the basic physics of DNA condensation. DNA condensation involves self attraction in a (semi)flexible polyelectrolyte. Attraction between multiple polyelectrolytes occurs in the related case of bundle formation. Here, many single persistence length DNA (i.e. charged colloidal cylinders) aggregate to form bundles. In all these cases the effective attraction is short-ranged and requires multivalent counterions. Condensed DNA spontaneously forms in the simulations with tetravalent or trivalent counterions. No condensates are stable for divalent counterions. Condensation occurs because electrostatic interactions dominate entropy, and the favored Coulombic structure is a charge ordered state. In the simulations of multiple DNA molecules of single persistence length, bundle structures form in the presence of divalent counterions. In this case, because the condensed counterions occupy the larger multiple molecule volume, their entropy is greater and the collapse of the system can occur with a smaller counterion valence.


260

Giant Charge Inversion of Macroions Due to Multivalent Counterions

Motohiko Tanaka, National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan; A.Yu Grosberg and B.I.Shklovskii, Department of Physics, University of Minnesota, 117 Church Street SE, Minneapolis, MN 55455

Charge inversion of macroions which arises from strong electrostatic inter-particle correlations is studied by molecular dynamics simulation. The charge inversion is seen to occur by attachment of multivalent counterions on the macroion; it occurs when (1) multivalent counterions with valence Z >=2 are present, and (2) the Coulomb coupling parameter is larger than unity. The latter condition is required to enhance the counterion binding on the macroion and to suppress the coion condensation on the counterions. Large charge inversion that amounts up to 200% that of the macroion original charge is observed. The amount of inverted charge Q scales as Q~x^(1/2) for small x<1 and as Q~x for large x>1. Here x is the square of the ratio of the Wigner-Seitz cell radius and the Debye screening length, which is proportional to the valence and density of the counterions. When an external electric field is applied, the charge complex of macroion and counterions drifts along the electric field in the direction implied by the inverted charge as long as the electric field is not large enough as to dismantle the charge complex into separated macroion and counterions.


261

Crystallization of Membrane Proteins in Surfactant Mesophases

Kelly Kochvar, Marlene Mekel, Matthew Lynch, Rick Walter and Bobby Barnett, Corporate Research Division, the Procter & Gamble Company, Miami Valley Laboratories, 11810 E. Miami River Road, Route 27, Cincinnati, Ohio, 45061 and Procter & Gamble Pharmaceuticals, Health Care Research Center, Mason, Ohio.

Membrane proteins are particularly difficult to crystallize due, in part, to the presence of large hydrophobic domains which tend to denature outside their native membranes. Current techniques require the addition of detergents (surfactants) which form micelles about the hydrophobic domains, stabilizing them in solution. Surfactant mesophases offer a novel method for stabilizing membrane proteins. The structure of the mesophases is based on bicontinuous bilayers of surfactants. It is postulated that the bilayers act as a ‘host’ membrane which stabilizes the hydrophobic domains; the bicontinuous structure provides a pathway for assembly of the crystals. The use of mesophase in the crystallization of membrane proteins is will be discussed


262

Simulation of Protein Self-Assembly

Arthur C. Hewig, Todd M. Przybycien, Department of Chemical Engineering, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213, Jeffrey A. Bell, Wadsworth Center, New York State Department of Health, P.O. Box 509, Empire State Plaza, Albany, NY 12201.

We are developing a grand canonical Monte Carlo simulation of protein self-assembly. The goal of this work is to determine if it is possible to predict the crystallizability for a particular protein molecule in a particular crystal system. We are using a united atom approximation of the target protein molecules using the data files from the Protein Data Bank (PDB). The protein molecules are assembled onto a fixed crystal lattice and have a discrete number of possible orientations. The interaction energies between neighboring protein molecules are determined using knowledge based potentials, which were calculated from 225 PDB data files. During the simulation, the packing is observed at a range of chemical potentials. A number of different proteins and crystal forms of each protein have been investigated. At sufficiently high chemical potentials the simulation predicts the crystallographically expected assembly in greater than 90% of all protein/crystal systems tested. It is hoped that this simulation can be used to predict the crystallizability of mutant proteins.


263

Induced Strain Fields in Hard Sphere Crystals and Glasses

Andrew D. Hollingsworth, William B. Russel, Department of Chemical Engineering, Christopher K. Harrison, Matthew T. Sullivan, Paul M. Chaikin, Department of Physics, Princeton University, Andrew B. Schofield , Department of Physics and Astronomy, University of Edinburgh

Specially synthesized fluorescently dyed poly(methyl methacrylate) spheres were used to investigate the strain response of hard sphere colloidal crystals and glasses. The stress was imposed by the harmonic motion of a larger (10-micron diameter) polystyrene sphere submerged in a colloidal suspension of sterically stabilized, 0.92-micron spheres. Using the optical cross-sectioning capability of a confocal (Nipkow disk) microscope, we measured the position of the colloids in three dimensions. The sphere centers were tracked to within 10 nanometer accuracy at the symmetry plane in order to determine their response as a function of time and position. An optical tweezer trap was used to manipulate the larger particle. Comparison of the strain fields and viscoelastic properties for the glass, liquid and solid will be presented.


264

Polymer Crystallization from Dilute Solution

P. Welch and M. Muthukumar, Polymer Science and Engineering Department, University of Massachusetts, Amherst, Massachusetts 01003

We are employing Langevin dynamics simulations to provide a molecular level view of polymer crystallization. We find that crystallization from dilute solution is essentially a five step process.

First, our simulations suggest that a nucleation and growth mechanism gives birth to seed crystals in the initial stages of homogeneous crystallization. Second, chains diffuse to the lateral face of the seed crystal. Third, the chains simultaneously adsorb and crystallographically (planar zig-zag conformation) attach to the crystal - no free energy barrier is observed for this step. Fourth, the newly added chains undergo a rearrangement on the growth front. Fifth, chain dynamics within the crystal result in an overall thickening of the lamella. The simulations demonstrate experimental observations including a linear lateral growth law and the formation of growth sectors.


265

Phase Behavior of Anisotropically Interacting Protein Systems: Effect of Long Range Depletion Attractions

Amit Kulkarni and Charles Zukoski, University of Illinois, Urbana-Champaign, Department of Chemical Engineering, 114 RAL, Box C-3, 600 S. Mathews Ave., Urbana, IL 61801

In simple colloidal dispersions as well as in protein solutions, the phase behavior is largely influenced by the range of interparticle interactions. In isotropically interacting systems, long range attractions result in stable colloidal gas, colloidal liquid and crystal phases, while as the range of attraction decreases, the gas-liquid transition becomes metastable with respect to the fluid-solid boundary. The existence of metastable gas-liquid transitions in protein solutions has been attributed to the presence of such short range attractions in these systems. Generalized phase diagrams have been developed experimentally by linking the second virial coefficient (B2), which is a measure of strength of interactions, to solubility (Rosenbaum et. al., J. Chem. Phys. 111, 9882, 1999). Simple fluid models based on particles interacting with short range isotropic attractions are found to predict the experimentally observed solubility (fluid-solid) boundary accurately. However, the models fail to capture the measured metastable gas-liquid boundary and the location of the metastable critical point. Recent work suggests the evidence of anisotropic, highly directional interactions in protein systems. In this paper, we use a model developed by Sear (R. P. Sear, J. Chem. Phys. 111, 4800, 1999) for globular proteins interacting with short range anisotropic attractions to calculate the phase behavior and compare it with our experimental results. The model captures the solubility boundary as well as the location of the metastable critical point fairly well. We have earlier investigated the role of long range depletion interactions induced by the addition of polymer on the phase behavior of protein solutions (A. Kulkarni & C. Zukoski, J. Cryst. Growth, in press, 2000). Here, we incorporate depletion attractions along with anisotropic interactions and calculate phase diagrams and compare them with the experimental results. The effect of long range depletion interactions on the phase behavior of anisotropically interacting particles is thus presented.


266

A Rapid Method for Quantitatively Measuring the Second Osmotic Virial Coefficient for Proteins

Peter M. Tessier, Stanley I. Sandler, Abraham M. Lenhoff, Department of Chemical Engineering, University of Delaware , Newark, DE 19716, USA

The second osmotic virial coefficient (B22) is a valuable thermodynamic property for understanding protein phase behavior (e.g. crystallization). However, current methods for characterizing protein interactions, such as light scattering or osmometry, are expensive in terms of both time and protein. Therefore, we are developing a faster, more efficient method for quantitatively measuring protein interactions using a relatively new technique called self-interaction chromatography (SIC) (Patro and Przybycien, 1996). The basis for SIC is that protein is immobilized on chromatographic particles that are packed into a column and then the same protein is passed through the column. The relative retention of the protein reflects the average protein-protein interactions. Using statistical mechanics, we have related the retention factor (k') to B22, which is commonly used to describe protein interactions. We have` immobilized lysozyme and a-chymotrypsinogen on Tosohaas Formyl particles, and our B22 values are in quantitative agreement with those measured by light scattering, yet our method requires an order of magnitude less time and protein. Another advantage of this method is that interactions between different protein molecules can be measured directly. We have measured BSA/lysozyme and ovalbumin/lysozyme interactions, which show surprising trends that are in agreement with ultrafiltration and two-protein precipitation results.


267

Hydrodynamic and Electrokinetic Properties of Decane Droplets in Aqueous SDS Solutions

Dr. Michael Bevan, School of Chemistry & Department of Chem. Eng., Sarah Nespolo, Dr. Geoff Stevens, Department of Chemical Engineering, Dr. Derek Chan, Department of Mathematics and Statistics, Dr. Franz Grieser, School of Chemistry, University of Melbourne, Victoria, 3010, Australia

The interpretation of an oil droplet’s surface potential from its electrophoretic mobility is the same as that for a hard particle, except that the effect of interfacial momentum transfer on the droplet hydrodynamic mobility coefficient must be considered. Although the solution for a fluid droplet’s drag coefficient is well known, its experimental measurement is difficult, and its interpretation is complicated because of the adsorbed stabilizing surfactant and possible droplet deformation. This work interprets measured electrophoretic mobilities as zeta potentials for SDS stabilized decane droplets by using light scattering to measure the oil droplet hydrodynamic mobility coefficient. Static and dynamic light scattering were used to measure droplet size, shape, and diffusion. For all SDS concentrations used here between 0.01 mM and the SDS CMC, the droplet hydrodynamic mobility coefficients were identical with that of a hard sphere indicating no momentum transfer at the droplet surface into the interior fluid. The light scattering results also indicate monodisperse spherical droplets which display an increasing radius with increasing SDS concentration. The percent ionization, or degree of counter ion binding, was considered by comparing surface charge with the SDS adsorbed amount inferred from static interfacial tension data. The zeta potentials of the SDS stabilized oil droplets were found to be near 100mV for all SDS concentrations.


268

Classification of Colloidal Dispersions by Electrophoretic Fingerprinting

A. A. Morfesis, Malvern Instruments, Inc. Southborough, MA 01772 and R. L. Rowell, Department of Chemistry LGRT-701, 710 N. Pleasant Street, Amherst, MA 01003-9336

An electrophoretic fingerprint is the contour diagram of the electrophoretic mobility as a function of pH and pl , the logarithm of the system conductivity. We have shown that it is possible to characterize any colloid dispersion in situ, rapidly and non-invasively by electrophoretic fingerprinting. Some specific examples have been sulphate, carboxyl and amidine-carboxyl zwitterionic latexes as well as different dispersions of titanium dioxide. The prospects for identification of such surfaces by the new four-point fingerprint approach is discussed and evaluated for specific cases.


269

High-Speed Dispensing of Nanoliter Droplets on A Substrate Using Dielectrophoresis

T. B. Jones, Department of Electrical and Computer Engineering, University of Rochester, Rochester, NY 14627 (USA), M. Gunji and M. Washizu, Department of Mechanical Engineering, Kyoto University, Sakyo-ku, Kyoto, 606-01 (JAPAN)

Simple co-planar electrodes, embedded in an insulating layer and excited by rf voltage ≥100 kHz, can be used to manipulate small volumes of liquid (water included) on a substrate. The scheme exploits the well-known dielectrophoretic (DEP) effect, whereby liquid collects in regions where the electric field is most intense. On a slightly hydrophilic surface covering the co-planar electrodes, water movement is very rapid; meniscus velocities exceed 50 mm/s and multiple droplets -- at least 4 at a time -- form in less than 0.05 s. We have successfully formed droplets down to ~1 nanoliter, and there is evidence that sizes well below 0.1 nanoliter are attainable. The DEP microfluid dynamics of nanoliter volume manipulation and droplet formation are very interesting and not well-understood. Even with ~ 30 µm electrodes feature size, DEP dominates surface tension; however, there is evidence of a strong influence of the rf field upon surface wetting. Because our electric field is at much higher frequency than the values used in recent "electrowetting" investigations, it is unclear whether or not some new mechanism is involved. This paper provides a quantitative description of DEP microfluid dynamics and presents models to explain certain observations.


270

Surface Charging Behavior for Single Wall Carbon Nanotubes in Ethanol Suspensions

L.A. Woods, J.H. Adair, 217 Materials Research Laboratory, and P.C. Eklund, 210 Osmond Buildng, Penn State University, University Park, PA, 16802,

Single wall carbon nanotubes (SWNTs) have potential in a wide variety of applications including electrochemical nanoprobes, supercapacitors, battery electrodes and spin transport electronics. However, each of these potential applications depends on handling and manipulation of the SWNTs into specific orientations and ultimately specific structures. Another issue is the deaggregation of bundles commonly produced during bulk synthesis of the SWNTs. Some of the potential techniques for manipulation of the SWNTs are based on colloidal techniques where packing via self-assembly techniques can be employed or more familiar particle suspension techniques such as colloidal casting can be used to produce particle compacts. In any colloidal processing technique, the nature of the surface charge provides the fundamental basis for solution chemical manipulation to achieve the desired colloidal behavior such as packing or dispersion. In the current study, the surface charge as function of acid and base concentration in a non-aqueous solvent, ethanol, has been determined using a phase angle light scattering technique to determine the zeta potential on particle surfaces. It is shown that the zeta potential is negative over a relatively large range of acid and base concentrations similar to the charging behavior observed for colloidal diamond and other carbonaceous materials.


 

271

Electroacoustic Measurements in Concentrated Colloids

Richard O’ Brien, Colloidal Dynamics Inc., Product Development, Unit 25, The National Innovation Centre, Australian Technology Park, Eveleigh, 1430, Australia

Electroacoustic measurements involve either the generation of ultrasound by an applied electric field or the reverse effect where a sound wave disturbance generates electric fields in a colloid. The output signal in each case is related to the particle size and zeta potential in the colloid. One of the great attractions of this technique is that it can be applied to concentrated suspensions. Indeed, the more concentrated the suspension the stronger the effect. In this talk I will show how we go about using electroacoustic measurements to determine the zeta potential and particle size in a concentrated colloid, and I will present results for a number of colloidal systems.


272

Rotational Electrophoresis Can Be Used to Measure Charge Nonuniformity

Darrell Velegol and Jason D. Feick, Department of Chemical Engineering, Penn State University, University Park PA 16802

Classical theories for colloidal forces have assumed uniform charge distributions on the particle surfaces. But a few recent papers have shown that a nonuniform charge distribution on two colloidal particles will significantly change the normal colloidal forces (i.e., those forces acting along the line of centers between the particles) and produce tangential colloidal forces (i.e., those forces acting laterally along adjacent surfaces) between even non-touching particles. Thus, nonuniform charge distributions can cause unexpected suspension stability, structure, and rheology. We are combining microelectrophoresis experiments with electrokinetic theory to measure the charge nonuniformity on individual particulates of PS latex, silica, and bacteria. Since a random distribution of zeta potential on a particle surface will in general result in an electrical dipole, nonuniformly-charged particles rotate in an applied electric field. We observe the angular velocity during this rotation. We have also developed the electrokinetic theory required to interpret the measurements, and so we are able to measure the first moment (average) and second moment (standard deviation) of zeta potential on particle surfaces. Early data support the fact that charge nonuniformity could be a cause of colloidal instability.


273

Enhanced Mixing in the POTF of Fenestrated Soft Contact Lenses: Theory and Clinical Experiment

K. L. Miller1, A. Chauhan2, K. A. Polse1, and C. J. Radke2 School of Optometry1 and Chemical Engineering Department2, University of California, Berkeley, CA 94720-1462

Efficient flushing of bacteria and cell debris from the thin post-lens tear film (POTF) underneath a soft contact lens (SCL) is very important for safe extended wear. Mixing in the POTF occurs by convection-enhanced diffusion or dispersion due to time-periodic lateral (up-down) and transverse (in-out) lens motion during blinking. The dispersion coefficient scales by the square of the amplitude of both motions. To enhance transverse motion and thereby improve tear exchange, we investigate the mixing behavior of fenestrated SCLs. The hydrodynamic equations of motion are solved for Newtonian fluid transport in the POTF assuming lubrication. Pressure profiles are integrated to determine the transverse lens travel with fenestrations present. This travel is divided by that in the absence of fenestrations and squared to predict mixing efficiency. Fluorescein flushing times are measured for 15 human subjects each wearing a fenestrated 14-mm diameter, silicon-hydrogel lens and then an otherwise identical unfenestrated lens. Fenestrated lenses contain 2 concentric but staggered rows of 40 holes, each 50 m m in diameter. The fenestrated lenses indeed enhance flushing efficiency by an average of about 25 % demonstrating feasibility of commercial use. Comparison of experimental and theoretical mixing times is qualitative as the theory depends strongly on the POTF thickness, a quantity not known for each subject.


274

Interaction, Between Surfaces Bearing Adhesion Sites and Sticky Fluid Layers

F. Pincet, E. Perez, C. Gourier, Laboratoire de physique Statistique de l'Ecole Normale Supérieure associée au CNRS et aux universités Paris 6 et Paris 7, 24 rue Lhomond 75005 Paris, France, L. Lebeau, Laboratoire de Synthèse Bio-Organique, Faculté de Pharmacie, URA1386, 74 route du Rhin, 67401 Illkirch, France, Y.M. Zhang, J. Esnault, JM. Mallet, P. Sinay, Département de Chimie de l'ENS, 24 rue Lhomond 75005 Paris

Adhesion through sites is very important in many applications involving functionnazlised materials and biology. We have measured the adhesion between surfaces bearing molecular recognition sites by using several techniques: the surface forces apparatus and vesicle micropipet aspiration. This way, it was possible to study the adhesion between two lipid bilayers deposited on mica, between a vesicle and a polymer bead, and between two vesicles. All the surfaces were functionalised either with nucleosides or with oligosaccharides. With the SFA, we will show how, with surfaces bearing a closed packed layer of adhesion sites, it was possible to deduce their binding energies from a very crude model. Once connected to the complementary sites, these layers behave as sticky fluid layers that flow under pressure. By measuring the adhesion energy between a bead and a vesicle bearing the same adhesion sites, it was possible to test theories developed in the 80's relating the adhesion energy to the binding energy of sites. We will also present the adhesion measurements with oligosaccharides involved in cell adhesion.


275

Thermocapillary Flow and Aggregation Of Bubbles On A Solid Surface

Hiroki Kasumi, Paul J. Sides, John L. Anderson, Department of Chemical Engineering, Carnegie Mellon University, 5000 Forbes Avenue DH1201, Pittsburgh, PA, Yuri E. Solomentsev, Motorola, 3501 Ed Bluestein Boulevard, Austin, TX

Theory suggests that thermocapillary flow about neighboring bubbles in liquids on hot walls pulls the bubbles together. A temperature gradient perpendicular to the wall establishes a surface tension gradient at the bubble-liquid interface, which in turn sustains a shear stress gradient that pumps adjacent fluid away from the wall. Bubbles are mutually entrained in this flow. The theory predicts that the aggregation velocity is proportional to the temperature gradient, the radius of the bubbles, and the derivative of the surface tension with respect to temperature; the velocity should be inversely proportional to the viscosity of the liquid. Bubble aggregation experiments under controlled conditions were performed to test the theory. Scaling the experimental bubble trajectories according to the theory substantially collapses all of the data onto a master curve, which suggests that the theory is correct. Calculated velocities agree with the experimental results when hindrance of bubble motion due to the wall is included. Values for the parameter that describes the hindrance effect are obtained from fitting the data to the theory, from independent measurements, and from direct hydrodynamic calculation. The results of the three determinations agree within 15% of the possible range of the value of the parameter.


276

Role of Micellar Interactions in Foam Lamella Stability

A.D. Nikolov and D.T. Wasan, Illinois Institute of Technology, Department of Chemical and Environmental Engineering, 10 W. 33rd Street, Chicago, IL 60616

The thinning of a single microscopic foam lamella in the presence of nonionic micelles has been studied by using the capillary force balance in conjunction with reflected light interferometry. It was observed that the foam lamella thins in a stepwise fashion (stratifies) by the formation of darker circular spots (an area inside the lamella which is thinner by one micellar layer). The effect of the foam lamella size on spot formation and expansion is the subject of the present study. Under the confinement effect of the lamella surfaces, the micelles inside the lamella self-organize in multilayered structures. The mechanism of the lamella stepwise thinning by the formation of spots has been explained in terms of the condensation of micellar dislocations (vacancies) inside the micelle-layered structure. By increasing the film area, the number of dislocations increases, and at a certain critical concentration of dislocations (or lamella size), they condense, a darker spot is formed, and the foam lamella stratifies. Further increases in lamella size cause the spot to expand in area. However, if the lamella size is decreased, the spot size begins to decrease, and at a certain lamella size, the spot disappears, and the lamella thickness increases by one micellar layer. The reversibility of stepwise decrease/increase in the foam lamella thickness has been explained as a result of condensation and evaporation of micellar dislocations inside the micelle-layered lamella structure.


277

Coupled Capillary Wave Fluctuations in Thin Aqueous Films on an Aqueous Subphase

Mark L. Schlossman, Departments of Physics and Chemistry, Ming Li, Aleksey Tikhonov, Dragoslav Mitrinovic, Department of Physics, University of Illinois at Chicago, Illinois, 845 W. Taylor St., Chicago, IL 60607, David J. Chaiko, Argonne National Laboratory, Chemical Technology Division, 9700 S. Cass Ave., Argonne, Illinois 60439

We demonstrate the formation of nanometer-thick aqueous films on aqueous bulk subphases from polymer-salt biphase mixtures. X-ray scattering is used to probe the coupled capillary wave fluctuations of the liquid-vapor and liquid-liquid interfaces of this thin film. The coupling constant for these fluctuations is given by B=1.4x1011 J/m4. Our x-ray and interfacial tension data determine both the effective Hamakar constant that characterizes the long-range interaction between the interfaces and the parameters that characterize the short-range part of the interaction.


278

Effects of Shear Flow on a Polymeric Bicontinuous Microemulsion

Kasiraman Krishnan, Timothy P. Lodge, Frank S. Bates, Department of Chemical Engineering and Materials Science, Department of Chemistry, University of Minnesota, 421 Washington Aven, SE, Minneapolis, MN 55455, Wesley R. Burghardt, Department of Chemical Engineering, Northwestern University, Evanston, IL 60208-3120

We have investigated the effects of shear flow on a polymeric bicontinuous microemulsion using neutron scattering, x-ray scattering, light scattering, optical microscopy, and rheology. The microemulsion consists of a ternary blend of poly(ethyl ethylene) (PEE), poly(dimethyl siloxane) (PDMS) and the diblock copolymer PEE-PDMS. The observations reveal four regimes as a function of shear rate. At low shear rates (regime I) Newtonian behavior is observed, whereas at intermediate shear rates (II) there is a development of anisotropy in the morphology which leads to shear thinning. When the shear rate is increased further, there is a breakdown of the bicontinuous structure, resulting in a flow-induced phase separation (III). Rheological measurements indicate that the shear stress is almost independent of shear rate. Light scattering experiments indicate the formation of a streak-like pattern in the phase-separated regime, and correspondingly a string-like morphology with micron dimensions is observed with video microscopy. Upon further increase of shear rate (IV), the sample behaves like a binary polymer blend with the block copolymer playing no significant role; the stress increases strongly with shear rate.


279

Rheology of Self-Assembled Crude Oil Wax Crystal Modifiers

Henry S. Ashbaugh, Robert K. Prud’homme, Princeton University, Department of Chemical Engineering, Olden St, Princeton, NJ 08544

Precipitation of long-chain paraffins presents significant crude oil recovery challenges from sea bed reservoirs. Polymeric wax crystal modifiers can improve oil rheology, though additive selection is complicated by uncertainties in the crude oil composition and mechanism by which the polymer interacts with the paraffin wax. We examine the behavior of a series of diblock and random polymers which self-assemble due to crystallization of one of the blocks in model oils . These assemblies serve as nucleation sites for long-chain paraffin precipitation, thereby attenuating the wax crystal morphology. The rheological properties of these model systems are correlated with the structures of the polymer assemblies determined by scattering methods to develop mechanistic rules for the screening of flow improving additives. Subsequently, we examine the efficacy of these self-assembled additives at improving the rheology of real crude oils.


280

Hydration Temperature Effects on Xanthan Solution Rheology

Anthony J. Meehan, Merck Research Laboratories, P.O. Box 4, WP78-204, West Point, PA 19486

Low shear viscosity and elasticity of a xanthan gum formulation depends on the batch temperature during xanthan hydration. Yield stress and viscosity above the yield stress are unaffected. Thus, settling rates can be reduced without increasing the xanthan concentration and process equipment requirements. Rheology of xanthan solutions in deionized water show a much different temperature dependence than similar solutions with trace salts. While the latter demonstrates a clear order-disorder phase transition, the former shows an additional transition at a lower temperature. For increasing temperature, after an initial viscosity decrease, xanthan in deionized water goes through a sharp vicosity and elasticity increase, followed by a drop similar to order-disorder transition. The first phase transition may reflect an increase in molecular overlap, and explain the dependence of low shear viscosity on hydration temperature.


281

Shear Induced Phase Transitions in Side Chain Liquid Crystal Polymers

Caroline Pajolle & Laurence Noirez, Laboratoire Léon Brillouin (CEA-CNRS), CE-Saclay, 91191 Gif-sur-Yvette, France.

Side-chain liquid crystal polymers (SCLCPs) are made of mesogens laterally attached to a conventional main-chain polymer. These thermotropic materials are technologically easy to process. Fundamentally, they are expected to show original rheological behaviours because of both polymeric and mesomorphic characters. In the absence of an external field, it has been shown that the liquid crystalline order acts on the main-chain conformation by reducing anisotropically its entropy. The equilibrium between the phase enthalpy and the polymer entropy is governed by the local main-chain/mesogen interaction which is thus the key parameter determining all the thermodynamical properties. In contrast with small liquid crystalline molecules [1] , the SCLCPs flow behaviour is almost not explored. From a theoretical point of view [2], the main-chain/mesogen coupling is a molecular constant. We prove that shear flow can act on this coupling. In the smectic phase of SCLCPs, the shear flow decreases the layer thickness leading to a tilted smectic C phase [3]. This property is emphasised in the nematic phase; close to the nematic-isotropic transition, the main-chain orientation with respect to the director changes from perpendicular to parallel. Above the transition, the flow leads to the appearance of an induced nematic phase in the isotropic one[4].

[1] Safinya, C, et al., Phys. Rev. Lett. 66, 1986 (1991).

[2] Wang, X.J. & Warner, M., J. Phys. A, 20, 713 (1987).

[3] Noirez, L., Phys. Rev. Lett., 84, 2164 (2000).

[4] Pujolle-Robic, C., Noirez, L., to appear in the 11 January issue of Nature.


282

Flocculation in Flowing Fiber Suspensions

D. J. Klingenberg, University of Wisconsin, Department of Chemical Engineering and Rheology Research Center, 1415 Engineering Drive, Madison, WI 53706

Concentrated flexible fiber suspensions tend to flocculate into discrete domains, or "flocs", which hinders our ability to produce uniform products. By adding small amounts of water-soluble polymers (WSPs), fiber suspensions can be made to flow homogeneously. Optimizing and exploiting this phenomenon process requires understanding the role of the WSPs. Using atomic force microscopy, we find that the primary role of the WSPs is to reduce interfiber friction. To probe the relationship between interfiber friction and suspension structure and rheology, we employ a particle-level simulation technique. Flexible fibers are modeled as chains of osculating rigid bodies connected by elastic hinges. Suspension behavior is determined by numerically integrating the equations of motion of many fibers simultaneously. These simulations show that in order to correctly reproduce experimentally observed behavior, one must include realistic fiber features in the model, such as fiber flexibility and permanent deformations. We also find that flocculation can arise solely from interfiber friction, and without the presence of attractive forces between fibers. Reducing interfiber friction indeed leads to homogeneous suspension flow, as observed experimentally. Current work focuses on quantifying the relationships between friction and measures of the suspension structure.


283

The Efficacy of the Two Body DLVO Theory of Colloidal Interactions in Describing the Flow of Concentrated Particulate Dispersions

T.W.Healy, D.V.Boger, D.Y.Chan, P.J.Scales, S.B.Johnson and Z.Zhou, Particulate Fluids Processing, Centre, Department of Chemical Engineering, University of Melbourne , Vic., 3010, Australia.

The DLVO Theory is a two body description that seeks to understand the observed properties of Colloidal Dispersions. Rarely do workers insist that the DLVO approach is applicable to, say, very dilute suspensions , where, for example, the coagulation kinetics is approaching a two body limit. It is true that many workers using conventional light scattering always insist that the volume fraction of scattering particles must be low to avoid multiple scattering problems. Having got satisfactory data, they then apply DLVO theory, which most often works extremely well. But take the case of studies of the rheology of concentrated (at and above 50% by volume). Experimentally there is no difficulty in getting reliable data at such volume fractions. When DLVO descriptions are applied to flow curve at these very high volume fractions, surprisingly there is impeccable agreement between theory and experiment. In the paper we explore the reasons for such agreement and consider both yield steress and complete shear viscosity flow curves to test the application of DLVO theory across a wide range of volume fractions that would seem to be well outside the situation one could approximate as a two body system..


284

Molecule-Mimetic Chemistry

George M. Whitesides, Department of Chemistry and Chemical Biology, Harvard University, Cambridge MA 02138

Self-assembly is a process that is relevant to the generation of structured aggregates at all scales of size. Chemistry has explored self-assembly in detail for molecules, and has developed a substantial understanding of this subject in that context. This talk will expand concepts of molecular self-assembly to the self-assembly of meso-scale objects (objects with sizes from 1 cm to 10 µm), in processes in which capillarity is the most important interaction contributing to the generation of structure.


285

Micelle-Assisted Formation of n-Alkanethiolate Self-Assembled Monolayers on Gold from Aqueous Solutions

G. Kane Jennings, Dong Yan, and Jeremy A. Saunders, Vanderbilt University, Department of Chemical Engineering, Box 1604 Station B, Nashville, TN 37235

We report the formation of n-alkanethiolate self-assembled monolayers onto gold from environmentally benign aqueous micellar solutions instead of traditional organic solvents. We have used micelles as vehicles to solubilize thiol adsorbates in water and facilitate their delivery to a gold surface. The kinetics of formation for alkanethiolate SAMs onto gold in aqueous micellar solutions are affected by the micellar concentration, aggregation number, and the surfactant charge. Long-chain thiols such as C18SH are far more soluble in micellar solutions with high aggregation number. In general, micelles composed of nonionic surfactants such as C12Em (m=5, 6, 7) are superior in solubilizing the thiols and facilitating the formation of the monolayer. The water-borne SAMs exhibit molecular structures that are more densely packed than those formed from common organic solvents. In addition, the water-borne SAMs provide enhanced resistances against charge tranfer from soluble redox probes. These results suggest that hydrophobic interactions contribute to the formation of a more defect-free structure when SAMs are formed in aqueous solution.


286

The Effect of Plasma Pretreatment on the Stability of An Octadecyltriethoxysilane Monolayer Self-Assembled on Mica

Joan E. Curry and Sungsoo Kim, Department of Soil, Water and Environmental Science, University of Arizona, Tucson, AZ 85721

A self-assembled organic monolayer is potentially an ideal substrate for covalently tethering biomolecules to solids such as mica. Octadecyltriethoxysilane (OTE) monolayers were self-assembled on bare and water vapor-plasma treated mica surfaces. The stability of the OTE monolayers on treated and untreated mica surfaces was studied as a function of relative humidity using a surface forces apparatus. Measurements of the monolayer compressibility and the thickness of the water layers adsorbed by the OTE were made as a function of relative humidity. The monolayers self-assembled on plasma treated mica adsorbed significantly less water and were less compressible compared to the untreated case. It is thought that the increased stability of the organic layer self-assembled on plasma treated mica is due in part to covalent bonding between the silanes and the hydroxyl groups on the mica surface introduced by plasma treatment. Such highly stable organic layers could be useful as base substrates for many biological applications such as biomolecular recognition and cell adhesion studies.


287

Alkyl Glucosides from Branched Hydrophobes, Their Use in Microemulsions and Cleaning of Hard Surfaces

Ingegärd Johansson, Christine Strandberg, Akzo Nobel Surface Chemistry AB, S-44485 Stenungsund Sweden

It has been shown that the spontaneous curvature of an interfacial layer between oil and water consisting of alkyl glucosides with branched hydrophobes of a certain structure can be close to zero. Thus microemulsions can be formulated with minor amounts of hydrophobic additives to fine tune the palissade layer. Usually branching contributes to a less rigid ordering and thus prevents lamellar structures in the one phase microemulsion. The solubilization of large oil molecules like triglycerides can be expected to increase. Since dirt in practical cleaning situations often is a mixture of different oils and greases, a broad solubilization capacity is an advantage. Detergency efficiency for alkyl ethoxylates show a strong connection between degreasing effect and the phase inversion temperature (PIT) of the system. Temperature can be used as the tuning parameter since ethylene oxide based non-ionics become more hydrophobic at higher temperature (cloud point). Alkyl glucosides show a different temperature behaviour, very seldom showing up as cloud points. Instead fatty alcohol addition changes the spontaneous curvature. Is the detergency efficiency for alkyl glucosides dependent on the alcohol/surfactant ratio in a similar manner to the dependency on the PIT of ethoxylate based systems? This paper gives results concerning microemulsions stabilized by branched alkyl glucosides. The oil phase is paraffinic hydrocarbon and the tuning additive fatty alcohol. The composition of the actual interfacial layer is calculated.The knowledge about the optimal packing in the interfacial layer thus achieved has been tested in a cleaning process for hard surfaces. The results will be discussed in terms of optimal spontaneous curvature and possible intermediate phases present in the cleaning solution.


288

Fabrication and Characterization of Tethered Polyelectrolyte Solloids

A. Campbell and P. Somasundaran, Langmuir Center for Colloids and Surfaces, Columbia University, New York, NY 10027

The adsorption, conformation and orientation of polymers and surfactants at the solid-liquid interface are important parameters controlling the behavior of colloidal systems. One problem with typical approaches in this area of study is that one has often to simultaneously consider both the adsorption and conformational state of the species involved. This study attempts to remove one of those degrees of freedom by end-tethering the polymer in question to the surface. Block copolymers of polystyrene and polyacrylic acid were adsorbed to a polystyrene-coated glass surface and subsequently end-tethered to the surface via entanglement. The solloids (surface colloids) formed by this process and their conformational behavior under varying solution conditions were investigated.


289

Assembly of Thin Polymeric Films Via Templating on Colloidal Particles

G.B. Sukhorukov, I.L. Radtchenko, A.A. Antipov, E.Donath, H.Möhwald, Max Planck Institute for Colloids and Interfaces Research, Golm/Potsdam, 14424, Germany

Assembling of polymers on colloidal particles by means of either controlled precipitation of polymers on the surface of colloidal particles by changing their solubility or by layer-by-layer adsorption of oppositely charged polyelectrolytes. Organic and inorganic colloid particles, biological cells and nanocrystals can be used as cores to assemble multilayer film. The size of cores may range from 50nm to tens of microns. Shell can be fabricated from charged and non-charged polymers, biopolymers, lipids, multivalent dyes and inorganic nanoparticles. The amount of precipitated polymer and the number of the alternating layers determine the shell thickness, which can be tuned in the nanometer range. Some colloidal templates can be decomposed at conditions where the polymer shell is stable. This leads to the formation of hollow capsules, which have a determined size, shape and wall thickness. The possibility to use various materials allows proper design of the shell. Combination of surface controlled precipitation and layer-by-layer assembly opens avenues for many applications, such as encapsulation of polymers, metallic shell formation, precipitation and crystallization of organic and inorganic substances in confined geometry of the hollow capsule. The permeability through the shell and release of the encapsulated materials can be controlled and modified by pH, ionic strength and solvents.


290

Preparation Of Surface-Modified Microparticles by Grafting-from Methods

Guodong Zheng and Harald D. H. Stöver, Department of Chemistry, McMaster University, Hamilton, Ontario, L8S 4M1, Canada

Surface-modified microparticles have been formed by grafting from the functional surfaces of narrow dispersed polymer particles, using both ATRP and ring opening polymerization (ROP). For ATRP grafting, the residual double bonds on poly(divinylbenzene) microspheres were converted to chloroethyl groups, which were then used as initiators for the ATRP of styrene (CuBr/bipyridine, 110 °C/11 h). While there was only a 5% increase in particle diameter, the linear polymer chains on the microsphere surface caused a distinct change in the particle packing. Highly ordered monolayers and multilayers were formed when suspensions of the modified microspheres were cast onto glass slides. The surface linear polymer chains likely facilitates the packing process. The surface hydroxy groups of poly(hydroxyethylmethacrylate-co-divinylbenzene) (40/60 wt%) microspheres were used to initiate the ROP of e -caprolactone in the presence of Al(Et)3 or Al(iPrO)3 as catalysts. The diameter of the microspheres increased by 32% and 16% for the Al(Et)3 and Al(iPrO)3 systems, respectively, with no change in the particle size distributions. The core-shell morphology of these microspheres is revealed by TEM, and the change in surface polarity is evident from the ability of the grafted microspheres to be dispersed in non-polar solvents such as toluene.


291

Controlled Particle Morphologies Via Water Borne Atom Transfer Radical Polymerization

Mir Mukkaram Ali and Harald Stover, McMaster University, Chemistry Department, Hamilton, Ontario, Canada L8S 4M1.

Atom Transfer Radical Polymerization (ATRP) has been extensively researched since its discovery in the mid-nineties. Recently, ATRP has been extended to water borne systems including emulsion polymerization and solution polymerization, and used to produce polymer particles possessing desirable morphologies. Achieving good control over particle morphology in such systems requires careful optimization of the polymer composition and architecture, of the polarities and solubility characteristics of both the ATRP initiator and catalyst, and of the nature of the oil-water interface. This involves careful choice of macroinitiators, catalysts comprised of hydrophobically modified ligands, and surfactant. The effect of these factors on particle morphologies will be discussed.


292

From Capsules to Matrix Structures: A New Approach Towards Interfacial Encapsulation

Anna Shulkin and Harald D.H. Stöver, McMaster University, Department of Chemistry, Hamilton, ON, Canada, L8S 4M1

Microcapsules have been prepared by an interfacial polyaddition reaction of styrene-maleic anhydride copolymers with water-soluble polyamines for the first time. The reaction between the maleic anhydride groups of the copolymer dissolved in the organic core solvent, and the aqueous polyamine, leads to the formation of polar cross-linked polymers that partition to the interface, producing microcapsules. When a polar, water-miscible core-solvent was used, the rapid formation of the polymeric wall at the interface was attributed to a combination of the interfacial reaction with a solvent-driven phase separation. In contrast, when non-polar core-solvents were used, wall formation proceeded solely by the interfacial reaction. In addition, the solubility of the copolymer in the core-solvent, copolymer loading, and the rate of polyamine addition, drastically affect the morphology of the formed particles, including transitions from microcapsules to matrix structures.


293

Porous Membranes Via Colloidal Templating

Werner A. Goedel, Hui Xu, Organic and Macromolecular Chemistry, OC3, University of Ulm, 89069 ULM, Germany

Porouse membranes have been prepared by filling the interparticle volume of colloidal monolayers with polymers, transfer these monolayers to substrates with openings in such a way that they cover the openings. Removal of the colliods, gives rise to arrays of densely packed nanometer sized pores of uniform diameter. Depending of the colloids and the material in between them, the pores can be either round or polyhedral with round edges.


 

294

Particle Sizing in the Structured Concentrated Dispersions Using Acoustic Spectroscopy

Andrei Dukhin, Philip Goetz, Dispersion Technology Inc, 3 Hillside Avenue, Mount Kisco, NY 10549

Acoustic spectroscopy is able to characterize the particle size distribution of highly concentrated slurries. Many independent experiments have confirmed this capability, but other measurements have recently discovered some apparent errors at high volume fractions. In particular, tests at the National Institute for Resources and Environment in Japan indicate problems with alumina slurries at volume fraction above 20%vl. Specifically, the Japanese scientists observe an excess attenuation that cannot be explained within the existing theoretical framework. We suggest that this excess attenuation can be explained by a build-up of structure in the concentrated dispersion and that this structure leads to an additional mechanism of sound attenuation that we call "structural loss". Adding this mechanism to the theory allows us to explain the observed excess attenuation and moreover to calculate the correct particle size from the experimental attenuation spectra. In addition, we are able to calculate a second Hookean coefficient which quantifies the particle structure, which means that in this case the acoustic spectrometer functions as both a particle size as well as a rheometer.


295

Development of a Simple Computer Code for Use in Predicting Stability Behavior of Emulsions.

John Mullay and Robert Pollack, The Lubrizol Corporation, 29400 Lakeland Blvd, Wickliffe OH 44092-2298

A computer code has been developed which can be used on a PC to predict settling or creaming behavior as well as particle size distribution in emulsions as a function of time, temperature and container size. Once the code is calibrated for the system of interest, empirical input data includes densities of both phases, phase volumes, viscosity of external phase, temperature and initial particle size distribution. The effects included in the program are Ostwald ripening, coalescence, flocculation and modified Stokes law settling. The simplest possible relationships are utilized in this first version in order to establish a baseline for future efforts as well as to introduce the fewest unknown physical assumptions. Empirical parameters are required for each of the effects which are taken into account. These can be calibrated on systems of interest with minimal experimental effort. It is envisaged that this code can be used in conjunction with structure activity programs to study the effects of molecular structure and processing parameters on the physical phenomenon of importance in both fundamental emulsion studies as well as commercial development efforts. Results are presented for some commercial emulsions prepared under a variety of conditions as well as for systems obtained from the previous literature.


296

Matrix Effects on the Fluorescence of a Poly(styrene-co-vinylcarbazole) Latex

Paul Conrow and Andreas Langner, Dept. of Chemistry, RIT, 85 Lomb Memorial Dr., Rochester, NY 14623

The fluorescence quenching of poly(styrene-co-vinylcarbazole) by 4-iodotoluene and poly(styrene-co-4-iodophenylmaleimide) is the focus of this study. The efficiency of heavy atom mediated quenching of the carbazole fluorophore in latex particles, polymer solutions, and films is presented. The quenching of the fluorophore by 4-iodotoluene in a latex exhibits Stern-Volmer behavior with a slope of 1400 M-1. This represents a 28-fold increase over the quenching efficiency in a homogeneous solution. The greater quenching efficiency within the latex is attributed to the enhanced concentrations of fluorophore and quencher within the individual latex particles. The local concentration of carbazole within each copolymer latex particle is ~0.5 M; whereas, its concentration based on total volume is ~1x10-4 M. Dynamic light scattering measurements of the emulsion yield latex particle diameters on the order of 50Å. Experiments that employ the monomer analog of polyvinylcarbazole give similar results. The Stern-Volmer plot of the fluorescence quenching of 9-ethylcarbazole by 4-iodotoluene in an aqueous SDS micelle has a slope of 1700 M-1. The slope for the homogeneous 2-propanol solution is 95 M-1. The quenching behavior of poly(styrene-co-4-iodophenylmaleimide) on styrene/vinylcarbazole copolymers in latexes, solutions, and polymer films is also presented..


297

A Study of Copolymer Networks Formed from Methacrylic Acid and Poly(ethylene glycol) Methylether Methacrylate.

Ester C. C. Goh and Harald D. H. Stöver, Department of Chemistry, McMaster University, 1280 Main St. W., Hamilton, ON, L8S 4M1.

Micron-size microspheres, swellable microgels and macrogels were formed by copolymerization of methacrylic acid with poly(ethylene glycol) methylether methacrylate (PEGMM) macromer in presence of varying amounts of ethylene dimethacrylate (EDMA) as crosslinker. The effects of single and binary solvent systems comprising dimethoxy ethane, 2-butanone, ethyl acetate and heptane on the network structure were explored. In addition to solvency, the effects of crosslinking, comonomer composition and the PEG chain length were studied. In analogy to earlier work with divinylbenzene, increasing the crosslinking level or decreasing the solvency again leads to a change of morphology from microgels to the larger and denser microspheres. In addition, however, in the present more polar system the comonomer ratio can be effectively used to change the polymer-solvent interaction, and hence drive related morphology changes. This involves both general polarity of the copolymer, as well as specific hydrogen bonding between the acid and ether moieties. The resulting hydrophilic microspheres respond to external stimuli such as pH and temperature changes. The cloud point of the microgels was influenced by the ratio of acid to ether functional The role of PEGMM macromers with different chain length as in-situ stabilizer during polymerization will be discussed.


298

Novel Hydrogels: Preparation and Characterisation

Matt Hearn, Brian Vincent, University of Bristol. School of Chemistry, University of Bristol, Cantocks Close, Bristol BS8 1TS, David Rodham, Zeneca Agrochemicals, Zeneca Agrochemicals, Jealots Hill International Research Centre, Bracknell, Berks RG42 6ET

Hydrogels are cross-linked polymer gels that exhibit a swelling response to changes in environment such as pH or temperature. Previous work has shown that Poly 4-vinyl pyridine hydrogels (cross-linked with di-vinyl benzene) swell at a critical pH, with a swelling ratio that is dependent upon cross-link density. In this work we present an amphoteric hydrogel system that exhibits a swelling response at two critical pH’s corresponding to the pKa’s of the component monomers. We also present studies in which the internal structure of hydrogels has been probed by size exclusion experiments, solvent relaxation NMR and Differential Scanning Calorimetry (DSC).


299

Effects of Surfactants on the Aggregation State and Gelation of a Hydrophobically Modified Polyelectrolyte in Aqueous Solutions

N. Plucktaveesak, R.H. Colby, 315 Steidle Bldg., Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 , L.E. Bromberg, Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139

Effects of adding various surfactants to aqueous solutions of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-g-poly(acrylic acid) (Pluronic-PAA) are studied. Aqueous solutions of Pluronic-PAA gel as temperature is raised, due to micellization caused by aggregation of poly(propylene oxide) (PPO) blocks. Added surfactant breaks up the copolymer aggregates and lowers viscosity of HMP solutions. Anionic surfactant starts to incorporate into the existing polymer micelles at the critical incorporation concentration, CIC, which is determined as the surfactant concentration at which the surface tension has a local minimum. It is found from the fluorescence emission experiments that this CIC is non-cooperative, in contrast to situation involving micelle formation. Moreover, added surfactant affects the gelation threshold temperature of the polymer solution (Tgel). The effects of surfactant addition may vary depending on both hydrophobicity and tail length of the added surfactant. We relate the hydrophobic-lipophilic balance (HLB) number to the change of Tgel upon adding nonionic additive. Depending on the HLB of the additive, Tgel can be increased (HLB>11) or decreased (HLB<11). The results imply that both hydrophobicity and tail length play important roles in the interaction of Pluronic-PAA micelles and the surfactant.


300

How Do Capillaries Form in Alginate Gel?

H.-H. Kohler, H. J. Treml, University of Regensburg, Department of Chemistry and Pharmacy, D 93040 Regensburg, Germany

If divalent metal ions diffuse into an alginate sol, the alginate chains are cross-linked by the metal ions and a gel is formed . Under appropriate initial conditions the gel develops a regular hexagonal pattern of capillaries with the capillary axes directed normal to the gel formation front. The capillaries have uniform diameter (8-300 µm). The pattern is the result of the chemical fixation of a microscopic hydrodynamic flow pattern arising in the immediate neighborhood of the gel formation front. Our model shows that capillary formation is a dissipative process driven by contraction of the alginate chains occurring during the cross-linking process. Structure formation takes place above a critical value of the rate of contraction. The critical rate is determined by a number of factors, such as thickness of the contraction layer, coefficient of friction between the contracting chains and the surrounding water, rate of displacement of the reaction front and effectiveness of convective transport of the alginate chains. The physical chemistry of capillary formation and the general model equations governing this process are described. Detailed models of the contraction velocity and the factors determining the critical contraction rate are discussed.


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