Poster Presentation Abstracts

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P 1

Interaction of Wheat Puroindolines with Lipids: An Insertion Study Using LB Monolayer Technique

S. C. Biswas,* L. Dubreil and D. Marion, Institut National de la Recherche Agronomique, Centre des Nantes, Unité de Biochimie et Technologie des Protéines, Rue de la Géraudière, BP 71627 - 44316 Nantes Cedex 03, France

Puroindolines are the major basic and cysteine - rich lipid binding wheat proteins with a unique tryptophan - rich domain. They are composed of two isoforms, puroindoline - a (PIN - a) and puroindoline - b (PIN - b). Both proteins are amphiphilic and they adsorb very rapidly at the air - water interface. They can also insert within lipid membranes through their tryptophan - rich domain. In our present work, we have isolated and purified both puroindolines and major lipids (NAPE, NALPE, DGDG, PC) from wheat seeds. The interaction of puroindolines (PIN - a and PIN - b) with lipid monolayers formed at the air water interface have been followed using LB monolayer technique. It has been found that both PIN - a and PIN - b insert in lipid monolayers. The extent of insertion depends on the nature of lipid as well as on the packing of the lipid molecules in the monolayers. Both PIN - a and PIN - b have found to have more affinity for phospholipids compared to glycolipids and the extent of insertion follows the order NAPE> NALPE > PC > DGDG. For every systems studied, it has been observed that after a critical initial surface pressure value, the insertion of proteins in the lipid monolayer is zero due to exclusion of protein molecules from the monolayer. The critical value of surface pressure where the extent of insertion of proteins is zero was found to depend from the nature of the lipid.


P 2

Study of Controlled Release of Model Drugs from the Polymer Matrices of 2-Hydroxyethyl Methacrylate and with its Copolymers of Tetrahydrofurfuryl Methacrylate

Mohammad A. Chowdhury, D.J.T. Hill, & A.K. Whittaker* , Department of Chemistry , * Centre for Magnetic Resonance , The University of Queensland, Brisbane, QLD 4072, Australia

The project involves with the study of the controlled release of model drugs from a range of glassy polymer systems. The polymer systems were based principally on 2-Hydroxyethyl methacrylate, HEMA, and its copolymers such as those involving Tetrahydrofurfuryl methacrylate. THFMA. In the drug delivery systems, body fluids, which are principally water, can diffuse into the glassy matrices, which then become rubbery, and so release the encapsulated drugs. The rate of release of drug depends on the uptake of water, and so on the rate of diffusion of water into the polymer matrix. The rate of diffusion of water into the polymer matrices and the release rates of two model drugs of two different molecular sizes has been examined. The homo and copolymers were prepared in a cylindrical form by free radical polymerization of monomers in a Teflon® mould. The model drugs, Aspirin and Vitamin B12 were incorporated into the polymer matrices at a range of loadings of the drug, and the effect of the drug on the initial properties of the glassy cylinders were investigated. The water uptake rate into the polymer cylinders over a range of temperatures for the homopolymer and at 370C for all copolymer systems were studied by both mass increase and solid state NMR measurements to yield the diffusion coefficient for ingress of water. The effect of the incorporation of the model drugs and their loading on the nature of the water diffusion front and on the structure and behaviour of water in these systems were examined by solid state NMR and DSC methodologies. The bulk rate of diffusion of the drugs from the polymers was measured by UV-Visible spectroscopy and NMR methods. The release rate of the drugs will be correlated with the water uptake rates. The diffusion coefficients of the drugs and the effect of molecular size of the drug on the diffusion coefficients will also be examined.


P 3

Aggregation and Precipitation Equilibrium of Casein in the Presence of Calcium and Phosphate

Chen Guo1, Bruce Campbell2, Ken Chen2, Abraham Lenhoff 1, Orlin Velev1

1Department of Chemical Engineering, University of Delaware, Colburn Laboratory, Newark, DE 19716

2Kraft Foods, Inc., 801 Waukegan Rd., Glenview, IL 60025

The calcium-induced aggregation and precipitation of b -casein were studied in the presence or absence of inorganic phosphate at pH 5.5 and 7.5. The precipitation curves with Ca2+ follow the theoretically suggested pattern of weak binding to form a slightly soluble complex. In accordance with the model, the precipitation curves at pH 5.5 have a larger induction period and steeper slope than at pH 7.5. The presence of phosphate leads to better precipitation of the protein, which can be explained on the basis of the formation of calcium phosphate microcrystals. The presence of these crystals leads to effects such as adsorption of protein on the crystals, cross-binding of the casein micelles, and formation of sturdy aggregates. The results are complemented by data from dynamic light scattering measurements.


P 4

Hydrophobic Interaction Between Endocrine Disruptors and bRliposome Complex

Izumi Kubo, Soka University, Tokyo

Cationic liposome and bacteriorhodopsin (bR) forms large complex by electrostatic interaction.

Generally speaking, endocrine disruptors have hydrophobic affinity to lipid membrane. In this study, Hydrophobic interaction of endocrine disruptor,nonylphenol, with bRliposome complex was investigated. BRliposome complex showed remarkable change in light scattering at300nm compared to bR. When nonylphenol interacted with bRliposome complex, light scattering increased. Such increase depended on the concentration of nonylphenol.


P 5

Kinetics of Albuterol Photolysis in a Tri-Phasic System.

Quamrul H. Majumder and Anthony P. Simonelli, Division of Pharmaceutics and Industrial Pharmacy, AMS College of Pharmacy and Health Sciences, Long Island University, Brooklyn, NY

Purpose. To understand the effects, mechanism and kinetics of a photo degradation in presence of different surfactant and oil concentrations in a tri-phasic micro emulsion Methods. Photo degradation behavior of albuterol free base (cation) in presence of a non-ionic surfactant, polysorbate 80 (Tween 80) and mineral oil has been studied. Albuterol was chosen as a model drugs as it partitions among those tri-phases. A novel photodegradation technique has been used to degrade drug. Degradation of albuterol was analyzed by RP-HPLC. Results. Under the condition of the experiment polysorbate 80 and mineral oil did not undergo photolytic degradation. The photolytic degradation rate of albuterol was inversely proportional with that of polysorbate 80 concentration. Interestingly, the surfactants effect was dependent on the concentrations of both albuterol and mineral oil. Rate of albuterol degradation was proportional to the increase of oil and drug concentration. However, in the case of high surfactant concentration the effect of oil seems negligible. Models explaining chemical changes have been developed. Equation to describe the degradation kinetics will be presented. Conclusions. This model could be used to investigate photolytic degradation kinetics and mechanism in multiphasic formulation and to obtain the applicable micro kinetics constant in all phases.


P 6

Spatially Directed Bacterial Attachment via Optical Trapping

H. Haruff, J. Munakata Marr, D.W.M. Marr, Colorado School of Mines, Golden, CO 80401

Optical trapping techniques have been used in a number of fields to manipulate micron-size colloids and biological objects in solution. This approach allows particles to be trapped in a region of high light intensity by focusing a laser beam to a diffraction-limited spot. We have developed an extension of the single optical trap to manipulate multiple particles simultaneously by rapidly moving a single laser beam. This scanning laser optical trap creates a time-averaged light intensity profile, effectively creating many traps capable of concurrently controlling multiple objects. We are currently using this technique to study how individual bacterial cells attached to a surface grow to form a biofilm. By creating a moving trap we are able to "catch" multiple cells, move them to a desired location, and attach them to a glass coverslip. The ability to create very specific bacterial attachment patterns will allow careful investigation into the effects of initial attached cell conformation on early stage biofilm growth.


P 7

Convective Self-Assembly of Colloidal and Biological Arrays by Electrophoretic Deposition

Junhyung Kim,1,3 Vanessa Dorn,1,3 Stephen Garoff,2,3 John L. Anderson,1,3 and Robert D. Tilton1,3. 1Department of Chemical Engineering, 2Department of Physics, 3Center for Complex Fluids Engineering, Carnegie Mellon University, Pittsburgh, PA 15213.

Patterned cell arrays on solid surfaces are of interest for potential biosensor and tissue engineering applications, as well as for fundamental studies of cellular physiology. Recent advances in cell array patterning have used surface chemical modification to create cell adhesion templates or corrals. Using yeast as a demonstration system, we have used an ac electrophoretic deposition technique to rapidly self-assemble dense clusters of similarly charged cells adjacent to an electrode surface. The origin of the inter-particle attraction is hydrodynamic, stemming from the electromotive force on ions in solution near charged surfaces under an externally applied electric field. The cell clusters can be patterned by shaping the electric field. Depending on the mode of operation, stable cell arrays may either be formed in tight adhesive contact with the electrode surface or in non-adhesive, secondary minimum confinement. In the latter case, arrays are reversible. To study the electrophoretic deposition mechanism in detail, we examine the relative motion between two negatively charged latex particles adjacent to the electrode surface. Here we examine the frequency dependence of the inter-particle interaction, the phenomenon of a stationary gap between two attracting particles, and the onset of sudden aggregation.


P 8

Investigation of Bacterial Exopolymers Utilizing Atomic Force Microscopy

Shaun T. Pardi and Bruce E. Logan, The Pennsylvania State University, 212 Sackett Building, University Park, PA 16802

Knowledge of the chemical and physical factors influencing bacterial adhesion is important for the bioremediation of contaminated soils and aquifers, particularly during soil bioaugmentation. Atomic force microscopy (AFM) is being used to obtain a molecular-level analysis of the interaction of bacterial exopolymers with surfaces that will lead to improvements in our understanding of bacterial transport in porous media. Successful AFM imaging of bacteria, however, requires reliable methods for anchoring the bacteria to surfaces. Otherwise, cells will be moved across the surface due to interaction forces between the tip and the cell. We are systematically examining techniques to attach bacteria to slides reported in the literature, such as a drop-and-dry technique, bonding with poly-lysine and an EDC/NHS reaction. These techniques are being applied to study the adhesion of several different bacteria including a lipopolysaccharide-deficient mutant of Escherichia coli. Bacteria are being simultaneously imaged using a fluorescent microsope and the AFM. With this technique, we can directly observe cell motion during AFM imaging. We will demonstrate that it is possible to anchor cells irreversibly, repeatedly scan individual cells, and obtain force curves on the microorganisms.


 

P 9

Effects of Biopolymer-Induced Forces on Bacterial Adhesion to Glass

Jamaica L. Prince1 and Richard B. Dickinson, Ph.D1,2, 1Department of Chemical Engineering and 2Biomedical Engineering Program, P.O. Box 116005,University of Florida, Gainesville, FL 32611

A feature of many bacteria of diverse genera is the production of highly hydrated, anchored extracellular polymers termed capsules. Capsules are a compact layer of polysaccharides extending from the cell wall of some bacteria. Encapsulated bacteria are frequently associated with serious invasive infections and bio-film formation. In our research laboratory we use a single-beam, gradient optical trap as a force transducer to directly measure the resulting forces upon probing a single bacterium, towards a glass slide. In this work we measure the interaction forces induced by the presence of extracellular polysaccharides. Our current studies of Staphylococcus show a marked difference in attachment rates due to the presence or absence of capsular material. The measured interaction forces, along with ancillary surface characterization, suggest that this disparity in kinetic rates is due to steric effects.


P 10

Solid-Solid Phase Transition Between Two Crystal Forms of Annexin V

Ilya Reviakine, Obe-rflachentichnik, Laboratory for Surface Science and Technology, ETH Zurich, Wagistr. 2, CH 8952 Schlieren, Switzerland, Wilma Bergsma-Schutter and Alain Brisson, Department of Biophysical Chemistry, GBB, University of Groningen, Nijenborgh 4, 9747 AG Groningen, the Netherlands, Alexander N. Morozov , Soft Condensed Matter group, LIC, Leiden University, PO Box 9502, 2300BA Leiden, the Netherlands.

A classical method for the 2D crystallization of soluble proteins, suchs as annexin V, is the so-called lipid monolayer technique, where 2D crystals are formed on a lipid monolayer incorporating a protein-specific ligand spread at the air-water interface (1). Our previous work had demonstrated the ability of SPBs to support 2D crystal formation (2). AFM enables the crystallization process to be followed in situ at molecular-resolution. In particular, a solid-solid phase transition between two crystal forms of annexin V was observed and the mechanism for the transition was proposed (3).

1. Uzgiris, E.E. & Kornberg, R.D. (1983), Nature 301, 125.

2. Reviakine, I., Bergsma-Schutter, W., Brisson, A. J. Struct.Biol. 121(3), 356-361 (1998).

3. Reviakine, I., Bergsma-Schutter, W., Morozov, A. N., Brisson, A. Langmuir, in press.


P 11

The Development of Techniques for Probing Protein Aggregation Behavior in Bioprocessing Environments

Angela M. Wilcox, Todd M. Przybycien, Carnegie Mellon University, 5000 Forbes Ave. Pittsburgh, PA 15213

Protein-protein interactions and protein aggregation phenomena are prevalent throughout the bioprocess industry. Aggregation, a primary mode of protein degradation, often leads to immunogenicity of the protein and a loss of bioactivity. Therefore, it is necessary to formulate proteins to minimize aggregation as even small amounts of contaminating aggregates in the protein drug can cause it to be unacceptable for delivery to patients. Prior research in our laboratory led to the development of a technique called Self-Interaction Chromatography (SIC) which exploits the specificity of protein-protein interactions to select excipients that act as physical stabilizers against aggregation. In the present study, we are assessing the potential of quartz crystal microgravimetry (QCM), a mass sensitive detection system, as a possible formulation development tool. We have applied QCM in an analogous manner to the SIC technique. In SI-QCM, protein is covalently attached to the gold electrode of a quartz crystal through a pegylated thiol. The protein-coated surface is then placed in contact with the same protein in solution at a particular condition and the change in frequency is monitored. This frequency change represents the extent of the protein self-interaction at the conditions employed. We varied solution conditions by altering pH, and the addition of excipients to find suitable non-aggregating environments for recombinant bovine and human growth hormone. SI-QCM enables the miniaturization of the SIC technique requiring smaller sample volumes, and the parallelization of the screening process, improving throughput.


 

P 12

Colloid-Induced Surface Enhanced Raman Spectroscopy Of Bacteria

L. Zeiri*, S. Efrima*, Y. Shabtai#, B.V. Bronk&, *Department of Chemistry, #Unit of Bio-Technology, Ben-Gurion University, P.O Box 653,Beer-Sheva, Israel 84105, &U.S. Air Force Research Laboratory at US ERDEC, SCBRD-RT, E5951, APG, Maryland 21010-523

Silver colloids are used as a tool to study microbiological systems via Surface Enhanced Raman Spectroscopy (SERS). The colloids are selectively produced on the exterior or in the interior of the bacteria, as revealed by TEM. SERS measurements yield detailed vibrational information about the bacterial environment adjacent to the colloids. We investigate four different bacteria, of Gram negative and Gram positive types (E. coli, A. calcoaceticus RAG-1, P. aeruginosa YS-7, and B. megaterium). For the externally treated bacteria the SERS exhibit intense and rich spectra dominated by spectral features in the region 1250-1600 cm-1, though more minor bands are observed down to 400 cm-1. The spectra of the various bacteria are very similar to one another. They are attributed to flavins, which are a major component of the bacterias cell wall.


P 12-A

An In Situ Spectroscopic Method for the Detection of the Attachment Chemistry of Biomolecules to Silanized Surfaces

Brian J. Ninness1,2, Doug Bousfield2 and Carl. P. Tripp1,3, 1Laboratory for Surface Science and Technology (LASST), 2Department of Chemical Engineering, 3Department of Chemistry, University of Maine, Orono, ME, 04469

An in situ infrared technique is described which allows the detection of adsorbed surface species on metal oxide particles in an aqueous environment. The usefulness of this technique for studying adsorption on metal oxide surfaces is demonstrated with the reaction of succinic anhydride on a aminosilanized silica surface. This reaction sequence is a common method used to prepare glass surfaces in the attachment of probe oligonucliotides for microarray biochip technology. The technique involves first formulating a "coating" comprised of high surface area, silica particles and a polyethylene (PE) binder in a suitable solvent. The resulting coating is applied to the surface of an internal reflection element and mounted in a flow through Attenuated Total Reflection apparatus. It is shown that the PE weakly perturbs about 25% of the surface hydroxyl groups and that all surface groups are available for reaction with adsorbates. The silica/PE is indefinitely stable in an aqueous environment and has advantages of at least 2 orders higher sensitivity and a wider spectral range over studies using oxidized silicon wafers.


P 13

Enhanced Heterogeneous Oxidation for Treatment of Mine Drainage

Jonathan M. Dietz, Brian A. Dempsey, Civil and Environmental Engineering, 212 Sackett, Penn State University, University Park, PA 16802

The objective was to enhance the oxidation rate of Fe(II) in mine drainage using suspended ferric oxide solids plus provision of O2. The long-term goal is to develop small-footprint treatment that produces high-quality solids that can be reused. Mine drainage from the Bird Mine underground pool (Johnstown, PA) was pumped through an anoxic limestone drain to add excess alkalinity. A pilot-scale reactor consisted of two-300 gal tanks, a complete-mix oxidation reactor followed by a clarifier tank. Ferric oxide solids were recirculated from the clarifier to the reactor. Reactor ferric iron concentrations of 1800 mg/l yielded Fe(II) oxidation rates of 1300 g /m2/d at pH 6.3. Typical abiotic oxidation ponds are designed to remove from 10 to 20 g/m2/d of Fe at pH about 6.5. Results were consistent with a heterogeneous rate constant of 2.2 x10-8 (mg/L)-1s-1 and Eact of 179 kJ/mol. The sludge had specific resistance to filtration (SRF) of 4´ 1011 m/kg and a coefficient of compressibility of 0.37. The SRF was similar to that observed for flocculent solids that are formed at higher pH, but the compressibility was similar to high-density sludges. Sludge was easily pumped at ~10% total solids, which is similar to high-density solids.


P13-A

Instrumental Studies of Lead Sorption onto a Calcium Alginate Based Resin

Lin Wang and Shunnian Wu and J. Paul Chen, National Univ. of Singapore, Chemical & Environmental Engineering Department, 10 Kent Ridge, Singapore

A calcium alginate based ion-exchange resin was applied in lead adsorptionl from the synthesized waste streams in batch reactors. The study shows that the resin can efficiently remove the lead with high capacity and rate. The removal increased with the increase of initial solution pH. The Langmuir adsorption equation well described the equilibrium data under various conditions. The maximum uptake capacity (qmax) for lead ions was found to be 3.24 mmol/g, which is much higher than that for regular adsorbents. In the presence of calcium or sodium electrolyte, the qmax value decreased to 1.12 and 2.49 mmol /g respectively, which indicates the existence of competitive effects between these ions. The result of surface complex analysis by XPS and FTIR verified the ion exchange mechanism.

Kinetic study on lead removal was also conducted under various conditions. It was observed that most of the metal ions were removed in the first 20 minutes and complete uptake was achieved in 90 minutes, which is much faster than most of other adsorption processes. The presence of calcium and sodium ions played some roles in the uptake kinetics. It was found that mass transfer was the controlling mechanism. A diffusion-controlled model was successfully employed in the simulation under various operational conditions.


P 14

Chemical Weathering of High-Temperature Waste Products and Mechanisms Responsible for Changes in Leaching Behavior

Kevin Gardner, Omer Uppal, Raphael Roman, Robert Carter, Recycled Materials Resource Center, Department of Civil Engineering, University of New Hampshire, 123 Nesmith Hall, Durham, NH 03824

It has been observed that waste materials from high-temperature processes are thermodynamically unstable in the natural environment and weather in a similar fashion to volcanic ash, although many times at a faster rate. Experiments were conducted with a variety of waste materials to accelerate the individual mechanisms involved in the geochemical transformation process (dissolution, precipitation, carbonation and pH reduction), and pH-dependent leaching experiments were used to characterize changes in the availability of heavy metals in the weathered waste. Mechanisms investigated for decreased heavy metal availability include increases in exchange capacity and substitution of heavy metals in newly formed mineral phases. Analytical techniques employed in this study include transmission electron microscopy, neutron activation analysis and x-ray diffraction. Waste materials being investigated are those with beneficial use potential that are of concern due to heavy metal leaching; these include coal ashes, municipal solid waste bottom ash, and aluminum dross.


P 15

Surfactant Solubilization of PAH Compounds from Nonaqueous Phase Liquids

Alex Hill, Leticia Bernardez and Subhasis Ghoshal, Department of Civil Engineering, McGill University, 817 Sherbrooke Street West, Montreal, QC H3A 2K6, Canada

The equilibrium partitioning of polycyclic aromatic hydrocarbon (PAH) solutes from multi-component nonaqueous phase liquids (NAPLs) into micellar surfactant solutions has been investigated in this study. Chemically complex NAPLs, such as coal tars, creosotes, and petroleum-oils have caused contamination at many sites. Surfactant flushing can potentially enhance remediation at such sites. Although several studies have investigated the solubilization of pure crystalline PAHs, and PAHs sorbed onto soils, the partitioning patterns of PAHs from multi-component NAPLs has not been reported. This research demonstrates the relationship between NAPL composition and the extent of solubilization by surfactant solutions. Equilibrium partitioning experiments were conducted in batch systems where the NAPL and aqueous phase (or surfactant solutions) were mixed but not dispersed. The NAPL employed in the experiments was a synthesized NAPL comprised of PAH compounds and hexadecane. Several polyethoxylated surfactants were used at supra-CMC doses. Henrys law satisfactorily described the partitioning of PAHs from hexadecane into water and into surfactant solutions. Selective solubilization of naphthalene over phenanthrene was observed, which is believed to be the result of competition for space in the micelles outer layers. From these results a predictive relationship between NAPL PAH mole fractions and micellar solubilization is presented.


P 16

pH and Ionic Species Effects on Sorption of PCP on Highly Weathered Soils from Brazil

Seunghun Hyun1, Linda S. Lee1, P. Suresh. C. Rao1,21Department of Agronomy, 2School of Civil Engineering, Purdue University, West Lafayette, 47907-1150 IN, USA

The sorption behavior of ionizable organic chemicals is complex due to pH-pKa dependent speciation, and the differences in affinities of the neutral and ionic species. For variable charge soil, predicting sorption of ionizable organic chemicals is further complicated by the pH and ionic strength - dependence on the surface charge density. Therefore, to appropriately predict sorption behavior of acidic pesticides in variable-charge soils, organic anion sorption to positive surface charges must be considered as well as the effect of pH and solution matrix on speciation of the organic acid and the soil surface. Pentachlorophenol (PCP) sorption isotherms were measured on three variable charge soils in calcium chloride, calcium phosphate and calcium sulfate solutions over a range of pH values. In the presence of phosphate and sulfate anions, sorption was reduced relative to chloride systems. Sorption data will be presented and discussed with regards to differentiating between the noncompetitive association of PCP with hydrophobic soil domains and competitive anion exchange of pentachlorphenolate with phosphate and sulfate on anion exchange sites.


P 17

Sorption of Ions Non-Ferrous and Noble Metals

G. Ospanova, Al-Farabi Kazakh State National University (KazGU), Faculty of Chemistry, 95-a, Karasai batyr str., Almaty, 480012, Kazakhstan

In connection with growth of extraction non-ferrous and noble metals an actual problem is usage of effective, accessible sorbents from local raw material. On many industrial plants of color metallurgy of Kazakhstan and NIS the manufacturing process of sorption of non-ferrous and noble metals with usage of ionits is stipulated. However given sorbents is cost expensive, is not produced in Kazakhstan. In KazGU are developed and recommended the new synthetic and natural sorbents of organic and inorganic types from local raw material for extraction, purification, analysis of non-ferrous and noble metals (Cu, Au, Ag, Pt, etc.). The synthetic sorbents are polymers from monomers available in Kazakhstan, stable in acidic and alcaline conditions, at different temperatures, on cost, as well as commercial ionits, but on magnitude of capacitance on copper and gold on 1-1,5 about greater. The adsorption properties of local natural sorbents previously modified and prepared to process, are determined by a feature of a constitution of pattern. The molecule-sieve properties are characterized by homogeneous pattern of internal pores, the sizes which one are commensurable dimensioned of molecules of an adsorbate. The natural sorbents are stable at pH from1to13.The adsorptive centers have or strong electron-acceptor, or proton-donor by properties, are stable at extremely temperatures, are characterized by high chemical hardness, are accessible, are cheap (cost on 1-1,5 about lower, than industrial synthetic ionits). Optimal conditions of preparing synthetic and modifying of natural matters for obtaining sorbents with given properties are determined. Is shown, that on a surface the polymer - metal complex will be derivated. The kinetics of a sorption both desorption of copper and gold is investigated. The sorbents are tested at extraction of non-ferrous and noble metals from different types of mineral raw materials (ores, concentrates, technogenic raw). The ion-exchange mechanism of formation of complexes is shown. New sorbents are good sorbents due to a large surface area, a developing pore structure, ability for ion exchange. Thus, the new high-effective synthetic and natural sorbents of an organic and inorganic types from accessible and cheap raw materials of Kazakhstan for non-ferrous and noble metals are developed and recommended.


P 18

Adsorption of Metal Ions onto Goethite: Single-Adsorbate and Competitive Systems

Paras Trivedi1, Lisa Axe1, and James Dyer2, 1Department of Civil and Environmental Engineering, New Jersey Institute of Technology, Newark, NJ 07102. 2DuPont Engineering Technology, Wilmington, DE 19898.

Adsorption of anthropogenically released toxic metals such as Ni and Zn to goethite effects their mobility and bioavailability in aquatic environments. In this research, studies were conducted to understand competitive adsorption of environmentally important metals such as Ni, Zn, and Ca onto the goethite surface. Adsorption edges conducted as a function of ionic strength suggest that these metals may be chemisorbed to goethite. The adsorption affinity follows the order of the inverse of the hydrated radii multiplied by the number of waters in the primary solvation shell: Zn > Ni > Ca. The single-site Langmuir model provided a good fit for the adsorption isotherm data; equilibrium constants were found to be independent of pH indicative of one type of adsorption reaction. Furthermore they suggest that transition metals have a greater affinity for the surface than alkaline earth metals. Analyses uncovered two types of sites on the surface of goethite: high affinity ones to which transition metals bind, and low affinity sites to which only the alkaline earth metals such as Ca adsorb. The single-site Langmuir model accurately described the competitive adsorption between Ni and Zn for goethite. However, no competitive effects were observed in Ni-Ca and Zn-Ca binary systems.


P 19

Ozonation of Produced Water

Costas Tsouris, Thomas Klasson, Angela B. Walker, Michele D. Dinsmore, David W. DePaoli, Chemical Technology Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN, 37831-6224.

Oil companies use seawater to facilitate oil pumping. This approach leads to pumping a mixture of oil and seawater. After separation of oil from water, the seawater contains dissolved organics, which have to be removed before disposal. An ozonation process has been investigated for the removal of organics from produced water. A major task of the investigation was to identify effective means to contact the gas phase containing ozone with the aqueous solution. It has been found that bubble diffusers in high-ionic-strength solutions produce bubbles of size as much as 10 times smaller than that in low ionic-strength solutions. The high surface area per unit volume of the dispersion produced by bubble diffusers has been found to increase the ozonation rate. Batch and continuous-flow experiments have been conducted and the produced carbon dioxide, water-soluble organic acids, as well as water insoluble organics were analyzed by infrared spectroscopy and gas chromatography. An evaluation of the results towards feasibility of large-scale ozonation processes for the treatment of produced water will be presented.


P 20

Adsorption of Polyoxyethlene Sorbitan Monolaureate and Sodium Dodecyl Sulfate on Subsurface Materials

Vlado Arsov, Nilufer Dural, Mark Tumeo, Lutful Khan, Civil and Environmental Engineering Department, Cleveland State University, Cleveland, OH 44115

Adsorption of Polyoxyethlene Sorbitan Monolaureate, a nonionic polyoxyethylenated phenol, and Sodium Dodecylsulfate, an anionic surfactant, on subsurface materials was investigated. The experimental data were measured through batch equilibration studies, at 23oC, in conjunction with total organic carbon and surface tension analyses. Equilibrium adsorption isotherms were generated on two clay samples, Kaolin and Ca-Montmorillonite, which were chosen due to their contrasting properties. Adsorption of surfactants on both clays showed a typical Langmuir behavior, characterized by a convex curve leveling off as the monolayer saturation uptake is approached. In all cases, maximum capacity for adsorption was reached above several times the critical micelle concentration. The difference in the surface area of the clays was directly reflected in their adsorption behavior. Ca-Montmorillonite adsorbed up to 40%-50% more surfactant than did Kaolin. Overall results indicated that magnitude of surfactant adsorption on both clays were at insignificant levels when low concentrations of practical applications are considered.


P 21

Role of Membrane Surface Roughness in Colloidal Fouling of Nanofiltration Membranes

Eric M. Vrijenhoek and Menachem Elimelech; Yale University, Department of Chemical Engineering, Environmental Engineering Program, P.O. Box 208286, New Haven, CT 06520-8286

Our past work proved that membrane surface morphology strongly influences colloidal fouling behavior of reverse osmosis (RO) and nanofiltration (NF) membranes. Membrane fouling was correlated to various measured membrane surface properties (zeta potential, contact angle, chemical composition, roughness) and results showed that regardless of the physical and chemical operating conditions, colloidal fouling was nearly perfectly correlated with membrane surface roughness. Atomic force microscope (AFM) images of fouled membranes also yielded valuable insight into the mechanisms governing colloidal fouling. AFM images clearly showed that during the initial stage of fouling, more particles deposited on rough membranes than on smooth membranes, and the particles preferentially accumulated in the "valleys" of rough membranes. This investigation presents a new perspective on the relationship between membrane surface roughness and colloidal fouling of two commercial thin film composite NF membranes by incorporating several different size silica colloids. Additional AFM work on clean and fouled membranes is combined with a mathematical model of colloidal deposition to provide a mechanistic explanation for why roughness is so important during the initial stages of particle deposition. The relationship between particle size and membrane roughness is also discussed.


P 22

Age Dependent Dynamics of Water in Hydrated Cement Paste

Piero Baglioni, Emiliano Fratini, Department of Chemistry, University of Florence, via G. Capponi 9, I-50121 Florence, Italy, Sow-Hsin Chen, Department of Nuclear Engineering, 24-209, Massachusetts Institute of Technology, Cambridge, MA 02139 USA, Marie-Claire Bellissent-Funel, Laboratoire Léon Brillouin (CEA-CNRS), CEA Saclay, 91191 Gif-sur-Yvette Cedex, France.

Understanding the state of hydration water in cement material and the way to control it, is likely to be the key to improvement of its ultimate strength and durability1. Here we investigate diffusional dynamics of water molecules in hydrated tricalcium silicate, a major component in ordinary Portland cement1, as functions of temperature, aging and additive. Spectra of incoherent quasi-elastic neutron scattering from hydrogen atoms were measured using a high-resolution chopper spectrometer having an energy resolution of 28 meV, thus probing mainly the translational dynamics of center of mass of water molecules2. The spectra were analyzed with an explicit dynamical model taking into account existence of two types of water: the "immobile water", presumably water bound inside colloidal particle component of the cement paste, and the "glassy water3", water imbedded in gel-like component filling spaces between the colloidal particles. The model fits very well all normalized spectra in an absolute scale over a range of spectrum covering an energy transfer of 300 meV. We deduced from these fits three important parameters: a Q-independent fraction of the immobile water p; a Q-independent stretch exponent b and the Q-dependent average relaxation time tbar of the glassy water, as functions of temperature, aging and additive. From trends of the age dependence of the first parameter, we obtain a quantitative picture of the kinetics of the curing process. From the other two parameters, age dependence of the dynamics of structural relaxation in glassy water has been established for the first time. We found that the additive has a dramatic effect on slowing down the curing process of the cement.


P 23

WITHDRAWN.

P 24

The Stabilization of Colloidal Solutions with Use of the Compositions Containing Hydrolyzed Polyacrylonitrile

V.A.Yaremenko, V.V. Malyarenko, V.V.Simurov, A.S. Makarov, Institute of Colloid Chemistry and Chemistry of Water of Ukraine National Academy of Science, 42, Vernadsky ave., Kyiv-03142., 03680, Ukraine

Acrylic polymers are the components of compositions (hipan, anilis and others) for a rising of suspensions stability. In the article is studied the ways to keep stabilizing properties of powdery stabilizing agents containing hydrolized polyacrylonitrile (HPN). HPN is amphoteric thorough carboxyl and amide groups which ratio depend on a degree of alkaline hydrolysis. In an acid medium a dissociation of the carboxyl group are close down thorough a specific complexing of carboxyl group proton; therefore HPN zwitter-ion exist as the cation. In an alkaline solutions the amide groups protoning is not occurred so the zwitter-ion transform to anion. Thus for HPN the ion-exchange adsorption (or HPN interaction with surface charges of dispersion particles) and salt-mechanism adsorption the ions of polyvalent metals (PM) depend on pH. It is found by the microelectrophoretic study of montmorillonite and kaolinite in HPN solutions that the dispersion particles are charged negatively at alkaline pH and it positively in acid medium, isoelectric point set at pH from 5,5 to 5,9 in dependence on HPN hydrolysis degree. Potentiometric, conductometric and electrokinetic studies show the colloidal properties of HPN solutions are not retained after dehydration by drying and following dissolving. The reason is a little content of hydrophilic groups and hydrophility loss that lead to unreversible interactions between macromolecule vicinal chains and can induce HPN coagulation. As result the technical characteristics of stabilised suspension (viscosity variations, antisalt-stability) can very degrade. For working the powdery stabilizing agents containing HPN it is necessary to prevent the coagulation induced by forming of the complex (within and intermolecules, with ions of hardness salts or with PM ions). The test data show the colloidal properties of the powdery stabilizing agents can improve by means of some organic additives (nitril-trimethyl-phosphonic acid, lignosulphonates, aliphatic alcohols, humic acids). In particular humic acids are polyzwitter-ions with high z -potential in alkaline medium and a tend to complexing PM ions. The effective stabilization of the mineral suspensions at use of the powdery stabilizing agents is obtained at pH 8,0-8,5. It seems the key-part agents retain carboxyl groups of HPN for the suspensions stability.


P 25

Electrostatic Self-Assembled Nanoarchitectures With Polyelectrolytes of Different Molar Mass

S. Schwarz1, J. Nagel1, A. Janke1, K.-J. Eichhorn1, W. Jaeger2, 1 Institut für Polymerforschung Dresden e.V., Hohe Str. 6, 01069 Dresden, 2Fraunhofer Institut für Angewandte Polymerforschung, Geiselbergstr. 6914476 Golm

Adsorption of polyelectrolytes offer a widespread potential for the modification of planar surfaces. The adsorption process depends mainly on the charge, polyelectrolytes molar mass, concentration and ionic strength. To study such effects in mono- and multilayers we used PDADMAC, PMADAMBQ (PC) with a molar mass from 5000 to 400000 g/mol and PSS from 70000 to 1Mio g/mol in the diluted and semi-diluted region. The alternating adsorption of PC and PSS was investigated by streaming potential, in-situ SPR, ellipsometry, AFM, REM and contact angle measurements. SPR and ellipsometric measurements revealed that the thicknesses depends strongly on molar masses and inonic strength. Moreover, the process was followed in-situ in short time steps. PMADAMBQ has a higher content of hydrophobic parts and leads to a higher charge concentration at the surface and thus accelerates drastically the multilayer build-up. However, AFM and REM shows that those layers are not smooth but highly porous. Such self-assembled multilayers can be used as structures on a nanoscale level. For further applications it is necessary to control the surface charge. The surface charge is characterized by the electrokinetic or zeta potential. The measurements gave infomation about the existence of acidic or basic groups.


P 26

Stability of Colloidal Silica

S. Schwarz*, H.-M. Buchhammer, K. Lunkwitz*, W. Jaeger**,*Institut für Polymerforschung Dresden e.V., Hohe Str. 6, 01069 Dresden, **Fraunhofer Institut für Angewandte Polymerforschung, Geiselbergstr. 69, 14476 Golm

Polyelectrolytes are used in many fields in order to influence the surface properties and also the stability and coagulation properties of disperse systems. The interfacial interaction between a solid substrate via an adsorption process from aqueous solution is a complex phenomenon. Some of the dominant factors in the adsorption process are the chemical and physical features of the molecular structure and the properties of the macromolecules. In order to describe the influence of cationic polyelectrolytes on the stability and flocculation of dispersed particles, the adsorption on particles of Silica was investigated. Poly-methacryloyloxyethyltrimethylammoniumchloride (PM) and poly-methacryloyloxydimethyl-benzylammoniumchloride (PMBQ) of different molar mass have been used. On silica the adsorbed amounts increase with the ionic strength. The zero point of charge and the shape of the zeta potential-pH plots vary with the surface coverage by the polycations. The properties of the electrochemical double layers of the particles play an important role in the flocculation process. Zeta potential is a quantity for the net charge at the shear plane and a characteristic of the adsorbed layer. The zeta potential and flocculation rates are influenced at different salt concentrations by the adsorbed amounts and characterise the flocculation of the particles. Stabilisation is accomplished at low salt concentration for PM and PMBQ near the plateau of the adsorption isotherm by electrostatic repulsion of the covered particles with reserved charge. At high ionic strength, only PM stabilises the particles sterically by osmotic repulsion of the long tails. For PMBQ, we found a large flocculation range with no stabilisation at high coverage.


P 27

Self-assembling Paramagnetic Organophilic Colloidal Particles

Sibel Turksen, Paul Russo, Department of Chemistry and Macromolecular Studies Group, Louisiana State University Baton Rouge, LA 70803-1804

The preparation and properties of organophilic silica dispersions and paramagnetic dispersions of silica colloids are investigated. Organophilic silica dispersions of spherical particles are prepared via Stöber method1. The particles are further investigated with IR spectroscopy, TGA and TEM. Paramagnetic particles are prepared according to Massart method2 and coated with silica to obtain stable colloids with isotropic interactions. Both paramagnetic and non-magnetic particles are further functionalized via silylation reaction followed by the attachment of PBLG, PCBL to the surface of these particles in order to observe the self-assembly of the polyglutamates.

Reference

  1. Stöber, W., Fink, A., and Bohn, E. Controlled growth of monodisperse silica spheres in the micron size range. J.Colloid Interface Sci.26, 62. 1968.
  2. Massart, R. Preparation of aqueous magnetic liquids in alkaline and acidic media. IEEE Transactions on Magnetics Mag-17, 1247. 1981.

P 28

Effects of Surfactant Distribution and Time-Dependent Surface Potential on the Coalescence Rate of DLVO Dispersions.

German Urbina-Villalba and Máximo García-Sucre, IVIC, Centro de Física, Apartado 21827, Caracas 1020-A, Venezuela.

Through the years the strengths and shortcomings of DLVO theory had been outlined. It is now customary to use this theory to understand the dynamic behavior of Oil/Water (O/W) emulsions stabilized with ionic surfactants, with respect to flocculation and coalescence at distinct ionic strengths. However, the common analysis disregards the effects of non-homogeneous surfactant distributions, time-dependent surfactant adsorption, and generally concentrates on the study of the interaction potential between drops of equal size uniformly charged. As a result, fitting of experimental data with analytical equations is likely to produce effective Hammaker constants and surface potentials, concealing the real interaction potential between drops, and its effects on emulsion stability. In order to study this problem a modification of a standard Brownian Dynamics algorithm was made. In the present Emulsion Stability Simulations (ESS), the evolution of a small 64-particle system is followed as a function of time and surfactant concentration. We consider the cases in which: (a) the available surfactant is homogeneously distributed among all drops up to a maximum coverage; (b) a surfactant concentration gradient persists during the whole simulation; and (c) the surfactant adsorption is time-dependent. Here, these three cases are compared and their effects on the coalescence rate discussed.


P 29

Mechanisms Controlling the Coagulation of Kaolin Clay Particles by a Cationic Polyacrylamide

Jing Shen and Harold W. Walker, Department of Civil and Environmental Engineering and Geodetic Science, The Ohio State University, 2070 Neil Avenue, Columbus, OH 43210

Polyacrylamides are used in a variety of environmental applications, from soil conditioners to water treatment plant flocculants. In this paper, the influence of cationic polyacrylamide (CPAM) on the coagulation kinetics of kaolin clay particles was examined. Particle stability experiments were carried out as function of CPAM size and charge density at pH 7 and a salt concentration of 0.001 M NaCl. Stability and electrophoretic mobility experiments with low molecular weight CPAM indicated that the coagulation kinetics of kaolin were controlled by a charge neutralization mechanism and polymer bridging was of minor importance. For both CPAM charge densities studied (20% and 55% cation substitution), maximum coagulation rates were observed at polymer dosages corresponding to minimum electrophoretic mobility. In experiments with high molecular weight CPAM, maximum coagulation rates again corresponded to minimum mobility values, further supporting charge neutralization as the dominant coagulation mechanism for this system.


P 30

Tuning Interfacial Properties Through Polymer/Surfactant Complexation

Alan D. Braem, K. Derek Berglund, and Robert D. Tilton, Department of Chemical Engineering, Carnegie Mellon University, Doherty Hall 1101, Pittsburgh PA 15213

Interfacial properties can be tuned by exploiting polymer/surfactant interactions. By changing the relative concentrations of polymer and surfactant or the ionic strength one can change the size and charge of polymer/surfactant aggregates. The adsorption of these polymer/surfactant complexes to solid/liquid interfaces is thus also quite sensitive to mixture composition. Interfacial properties such as layer thickness, surface excess concentration, and surface charge density can be tuned by choosing the composition of the bulk solution. Using optical reflectometry and streaming current measurements we observe changes in interfacial behavior for a Pluronic F108/SDS system and for a hydrophobically-modified cellulose/SDS system. In the Pluronic/SDS system, adsorption can be either prevented entirely or enhanced compared to the polymer-only case depending on the SDS and background electrolyte concentration. Furthermore, adsorbed amount and thickness of SDS-free Pluronic F108 layers can be altered by first processing the layer with SDS/Pluronic mixtures at various ionic strength. We also observe a change in adsorption reversibility: coadsorbed layers are reversibly adsorbed while layers containing only polymer are irreversibly adsorbed. In the cellulose/SDS system, surface concentration can be varied by adjusting the SDS concentration and the surface energy. We also find a historical dependence of the adsorbed layer indicating the presence of non-equilibrium states.


P 31

Characterization of Polymethacrylates by Direct Force Measurements with the Bimorph Surface Forces Apparatus

C. Froeck and F.J. Schmitt, Institute for Polymer Research, Dresden, Hohe Strasse 6, D-01069, Dresden, Germany, M. Gerst and H. Röckl, BASF AG Ludwigshafen, ZKD/K-Bi, D-67056, Ludwigshafen, Germany

For analyzing the interaction forces between two polymer surfaces the bimorph surface forces apparatus (MASIF) was used. The topography and the quality of the polymer surfaces was analyzed by SFM (Scanning Force Microscopy). Aqueous dispersions of Polybutylmethacrylate (PBMA) with and without additive and cross linked Polybutylacrylate were spin coated on the freshly prepared glass spheres. These samples were installed in the MASIF apparatus and the force vs. distance functions, i.e., the adhesion, were determined from the bending of a bimorph spring. It could be shown that thin smooth films of PBMA with and without additive could be prepared on glass spheres, whereas it was not possible to prepare a film with cross linked PBA which covers completely the glass surface. The direct force measurements were performed at room temperature under dry nitrogen atmosphere avoiding capillary condensation. The obtained force distance functions showed different behavior depending on the presence of additive during preparation. The use of additive leads to stronger adhesion and a different time behavior of the polymer surfaces.


P 31-A

The Importance of Adsorbed Cationic Surfactant Structure in Dictating the Subsequent Interaction of Anionic Surfactants and Polyelectrolytes with Pigment Surfaces

Brian J. Ninness1,2, Doug Bousfield2 and Carl. P. Tripp,1,3 1Laboratory for Surface Science and Technology (LASST), 2Department of Chemical Engineering, 3Department of Chemistry, University of Maine, Orono, ME, 04469

It is shown that the structure of an adsorbed cationic surfactant layer, and not the amount of adsorbed surfactant, dictates the subsequent adsorption of anionic species on negatively charged TiO2 particles. By selectively modifying the adsorbed cationic surfactant microstructure, it is shown that the order of addition of anionic surfactants and polyelectrolytes in pigmented aqueous systems is important. An in situ dynamic investigation of the adsorption of a cationic surfactant (C16TAB) onto the surface of a TiO2 colloidal film is discussed. By combining dynamic adsorption data from ATR spectroscopic measurements with information on the electrophoretic mobility, the structure of a C16TAB layer adsorbed onto a particulate TiO2 surface is determined. The protocol involves the use of anionic probe molecules to uncover the underlying C16TAB structure. At bulk concentrations below the critical micelle concentration (CMC), C16TAB is shown to adsorb as isolated patches with a defective bilayer structure on the surface of TiO2.


P 32

Elastomeric Membranes from Monolayers of Polymers with Ionic Headgroups

Werner A. Goedel, Organic and Macromolecular Chemistry, OC3, University of Ulm, 89069 ULM, Germany, Frank Mallwitz, Marita Blankenhagel, Claire Peyratout, Robert Heger, Max-Planck-Institut f. Colloids & Interfaces, 14424 Potsdam, Germany

Hydrophobic polymers with low glass transition temperatures and hydrophilic head groups form insoluble monolayers at the air-water interface of a thickness of 10 nm to  50 nm. 1 If these fluid monolayers are transferred to solid substrates with holes, they initially cover the holes as suspended membranes,  but usually rupture after drying.  However,  the originally liquid monolayers can be stabilised by vitrification or cross-linking. 'Thermoplastic' membranes have been prepared form polybutylstryrene transferred at elevated temperatures and cooled down below the glass transition temperature. 2 Elastomeric membranes have been prepared from polyisoprenes that have been cross-linked via irradiation with UV-light and from polyisobuten star polymers that physically cross-link themselves via aggregation of multiple ionic head groups. 3 These 10 to 50 nm thin membranes can span openings in the millimetre range.  Due to their elastomeric nature they can be deformed reversibly up to 100 % strain and thus, are suitable

building materials for micro-mechanical devices like membrane valves and pumps.

 

1H. Baltes, M. Schwendler, C. A. Helm, R. Heger, W. A. Goedel  Macromolecules 1997, 30, 6633

2W. A. Goedel, C. Peyratout, L. Ouali, V. Schädler: Advanced Materials, 1999, 11, 213-217

3W. A. Goedel, R. Heger,  Langmuir, 1998, 14,  3470


P 33

Structure and Phases in Molecular Layers of Exotic Liquid Crystals at the Air Water Interface

E.E. Kooijman; S. Primak; E.K. Mann, Kent State University, Department of Physics, Kent, OH 44242

Brewster angle microscopy (BAM), and surface pressure measurements were used to explore phases and structures within molecularly thin layers of banana shaped and polymeric liquid crystals at the air water interface. The BAM set-up used in this study allows imaging over large, centimeter sized, field-of-views, revealing very large-scale structures.


P 34

Adsorption Kinetics and Surface Relaxations of Aqueous Surfactant Solutions Using Drop and Bubble Shape Tensiometry

AV. Makievski1,2, G. Loglio3, P. Pandolfini4, V.B. Fainerman2 and R. Miller1,

1MPI of Colloids and Interfaces, D-14424 Potsdam, Germany; 2 IMPC, University of Donetsk, Ukraine, 3University of Florence, Italy; 4INROE, CNR, Florence, Italy

Using a new drop and bubble shape tensiometer PAT1 the adsorption kinetics at constant surface area and harmonic and transient relaxation studies have been performed. The higher homologues of the series of alkyl dimethyl phosphine oxides and oxethylated alcohols, investigated here exhibit surface reorientations as suggested from adsorption studies. The adsorption kinetics and the dilational rheological results are in agreement with each other and the theory. A quantitative analysis of the parallel studies with drops and bubbles demonstrate the limits at which loss of surfactants due to adsorption at the interface becomes essential and needs to be considered. The theory to describe the dynamic data is based on a thermodynamic model assuming two adsorption states, the composition of which is controlled by the surface pressure. It is shown that the shorter chain series members follow a Langmuir isotherm and the adsorption dynamics is described very well by the respective diffusion theory, while the compounds with longer chain lengths require the assumption of a reorientation model in order to find a quantitative explanation.


P 35

Domain Structures in Langmuir-Blodgett Monolayers of Stearic Acid

Brian G. Moore, Penn State Erie, The Behrend College, School of Science, Station Rd., Erie, PA 16563, M. Cynthia Goh and Bernie D. Sattin, Department of Chemistry, University of Toronto

80 St. George Street, Toronto, ON M5S 3H6

Atomic force microscopy of Langmuir-Blodgett monolayers of stearic acid on mica reveals a pattern of domain structures in the adsorbed film. The domains vary in size from submicron to more than 10 microns (the largest scan size). The difference in height between the domains is very small; in contact mode, the height difference between the domains is approximately 0.1-0.2 nm. Friction (lateral force) scans show that the regions corresponding to thicker monolayer have substantially higher friction. These observations are discussed in the light of the phase diagram for the stearic acid monolayer on the water surface.


P 36

Dynamic Interfacial Tension in Water/Oil Systems Containing In-Situ-Formed Surfactants

D. Rana, J. Amaya, and V. Hornof *, University of Ottawa, Department of Chemical Engineering, Ottawa, K1N 6N5, CANADA

Oil/water interfaces are commonly encountered in nature (oil reservoirs), industry (liquid-liquid extraction), as well as in various pollution-abatement situations (washing of soil). When a droplet of oil is trapped in the pores of a porous medium, a very high pressure drop is necessary to move it through the narrow passages connecting individual pores as such a process is associated with droplet deformation and an increase in interfacial area. The mobilization process can be facilitated greatly by reducing the oil/water interfacial tension (IFT). Surfactants are generally used to reduce the IFT. Alternatively oils often contain surfactant precursors such as organic acids that can be converted into in-situ surfactants by adding alkaline reagent.

In this study, experimental investigations have been carried out with the aim to elucidate the fundamental mechanisms for the lowering of IFT between acidic oil and alkaline aqueous solutions. Drop volume tensiometry was employed to measure the interfacial tension. A model oil was used composed of n-dodecane acidified by addition of lauric or linoleic acid. Experimental results revealed that such systems were characterized by time-dependent IFTs that were a function of acid as well as alkali concentration. In case of lauric acid, the IFT value decreased almost linearly as the alkali concentration increased. In the case of linoleic acid, on the other hand, the IFT value reached a minimum at a relatively low alkali concentration and then remained almost constant. The IFT value decreased with increasing the acid concentration for both lauric and linoleic acid.


 

P 37

Chiral Discrimination in Langmuir Monolayers Containing Membrane Lipids and the Enantiomer of Cholesterol

Douglas F. Covey, S. Lalithaa, A. Sampath Kumar, Emily J. Westover, Washington University School of Medicine, St. Louis, MO 63110, Keith J. Stine, Department of Chemistry, University of Missouri St. Louis, St. Louis, MO 63121

Cholesterol plays a key role in cell membranes. Through complex interactions with lipids and specific proteins, cholesterol affects the physical properties of membranes and the biological processes occurring within membranes. The molecule ent-cholesterol is the enantiomer of cholesterol, and has each of the chiral centers of natural cholesterol inverted. The preparation of ent-cholesterol entails a challenging, multi-step synthesis. Comparing the behavior of cholesterol and ent-cholesterol in model membranes should serve to reveal specific chiral interactions with lipids or proteins. Studies comparing the monolayer behavior of mixtures of ent-cholesterol with the phospholipid dipalmitoylphosphatidylcholine (DPPC) and with egg yolk sphingomyelin were carried out and compared to the mixtures with natural cholesterol. Monolayers of DPPC showed no chiral discrimination in their interaction with the two enantiomers of cholesterol. In contrast, monolayers of egg yolk sphingomyelin exhibited a stereoselective interaction, becoming more condensed in the presence of ent-cholesterol. The monolayers were studied using Pressure-Area isotherms and Brewster Angle Microscopy.


P 37-A

Dilational Elasticity of Soluble Surfactant Layers in the Presence of Aggregation and Molecular Re-Orientation

L. Liggieri*, M. Ferrari*, F. Ravera*, R. Palazzolo*, R. Miller, V.B. Fainerman#; *ICFAM-CNR, via De Marini 6, 16149 Genova-Italy; Max-Planck Inst. for Colloid and Interface Sci., Am Muelenberg 2,14476 Golm - Germany; # Internat. Medical Physico-Chemical Center, blv. Shevchenko 25, 340017 Donetsk-Ukraine.

Re-organisation processes occurring inside soluble adsorption layers, like surfactant re-orientation and aggregation, have been evidenced both directly by neutron reflection techniques or Brewster angle microscopy, and indirectly, by dynamic interfacial tension studies. Such circumstance is particularly significant considering that such behaviours have been observed in rather common non ionic surfactants, like polyoxyethylenated alcools (re-orientation) and long chain alcools, like decanol and dodecanol (aggregation). Here recent theoretical results about the dilational properties of soluble surfactant layers undergoing such kind of transformations, are reported. The frequency dependence of the dynamic surface dilational elasticity is calculated by a perturbative approach, accounting for the diffusional exchange with the bulk and for the internal re-organisation process. The results show specific features, like, for example, a local maximum of the elasticity phase in correspondence of the characteristic frequency of the internal process, which make the rheological investigation very promising to study the molecular orientation and aggregation processes at the interface. The results can also be utilised, under the proper limit conditions, to describe the dilational behaviour of insoluble layers, which can be particularly useful in the study of the aggregation process in LB monolayers.


P 37-B

Measurement of Dilational Properties of Liquid Interfaces by an Oscillating Drop Method

M. Ferrari, L. Liggieri, F. Ravera, V. Attolini, CNR-Istituto di Chimica Fisica Applicata dei Materiali, via De Marini 6, 16149 Genova, Italy

The dilational properties of adsorption layers are correlated to the dynamic adsorption mechanism and play an important role in many technologically relevant phenomena like liquid film dynamics, droplet/bubble coalescence, stability of foams and emulsions. A new Oscillating Drop/Bubble set up is presented here, which has been used to study these properties for both liquid/air and liquid/liquid interfaces. This method is based on the measurement of the capillary pressure across a spherical interface, as response to an imposed oscillation of the surface area. The method allows the dilational elasticity to be measured as a function of the frequency in a range from 0.1 to 100 Hz. The experiment theory needed for calculating the elasticity from the acquired pressure data is briefly sketched, and examples of experimental results are given. The utilization of this technique coupled to an adequate modeling of the rheological properties give the possibility to access all the processes involved in the adsorption dynamics.


P 38

Adsorptivity Properties of Surface and Particle Distribution Function

O.G. Bakunin, Russian Research Center, Kurchatov Institute, Moscow, Russia

In this work an equation is derived, connecting adsorptivity properties of surface in rarefied gas with the particle distribution function of this gas. The conduct of particles carry ballistic character. However is possible to use the distribution function only in case of extremely rare collisions. A probability theory method is used in this paper, in place of kinetic equation.

The theory provides an integral equation connecting ballistic particle distribution function with adsorptivity properties of surface . It is shown the degree to which "tails" can go into complete nonanalytic decision of the kinetic problem. The Distribution function by velocity in form Levi distribution is obtained. (Edited by Symposium Organizers to meet word limit.)


 

P 39

Kinetics and Mechanisms of Morphological Transitions in Systems of Block Copolymer Aggregates in Solution

Susan Burke and Adi Eisenberg, Department of Chemistry, McGill University, 801 Sherbrooke St. W., Montreal, Quebec, Canada, H3A 2K6

It is well know that certain asymmetric, amphiphilic block copolymers can form a systematic series of multiple morphologies in solution. Recently, the morphological phase diagram has been constructed for the copolymer PS310-b-PAA52 in dioxane / water mixtures. Three different aggregate architectures, spheres, rods, and vesicles have been observed in this system. The phase diagram also contains region where two different morphologies coexist. Once a given morphology is formed, it has been found that a sudden change in the solvent composition, near one of the phase boundaries, can induce a change in the structure of the aggregates. This concept has been employed in the study of the kinetics and mechanisms of morphological transitions occurring in the system mentioned above. To date, the sphere to rod and rod to vesicle transitions, as well as the reverse processes, have been explored. The sphere to rod transition occurs via a two-step mechanism involving the initial collision of spheres to form a "pearl necklace" structure, followed by the coalescence of the necklace to form a rod. The reverse transformation also proceeds in a two-step process. A bulb grows on one or both ends of a rod and then the bulbs are pinched off to release free spheres in solution. The rod to vesicle transition occurs by the initial flattening of the rod, growth of circular regions at the expense of the rod, the eventual formation of a bowl-like structure, and closure to form a vesicle. The transition from a vesicle to rod results from the collapse of a vesicle into bowtie structure, which grows from the center to produce a dumbbell-like aggregate. The dumbbell stretches until a rod is formed. It was found that the rod to sphere and the rod to vesicle transitions occur more slowly than the reverse processes.


P 40

The Analysis of Physical Mechanisms Involved in Emulsion Destabilisation by the Turbiscan Ma 2000

S.Desset1, O. Mengual1G, 1Formulaction S.A. 10, impasse Borde Basse - 31240 L'Union France

Colloids and dispersions are inherently unstable systems but they can be considered as kinetically stable if their destabilisation velocity is sufficiently short compared with their expected lifespan. The two major destabilisation phenomena affecting the homogeneity of colloids and dispersions are particle migrations (creaming, sedimentation..) and particle or aggregate size variations (coalescence, flocculation). The techniques currently employed to detect physical destabilisation are either simply the naked eye or analytical instruments (microscopy, spectroscopy, turbidity and particle size analysis). However, most colloidal systems and dispersions are quite concentrated and opaque and, as a result, fall outside the range of existing instruments. As a rule, dilutions have to be performed severely reducing the accuracy and the scope of these instruments. The TURBISCAN MA 2000 has been accordingly developed to fill this gap and to allow the analysis of the physical destabilisation of concentrated (up to 50%) and liquid dispersions (emulsions, suspensions, foams, etc.). In this paper, we report the results of our study of the instability analysis of different kind of emulsions with the TURBISCAN MA 2000.


P 41

Thermo-Chemical Demulsification and Demulsification Mechanism of ASP Flooding Produced Liquid

Wu Di, Chemical Engineering Research Institute of Tianjin University, Tianjin 300072

A demulsifier was developed for the thermo-chemical demulsification of O/W produced liquid of an ASP flooding project in Daqing Oilfield. The performance of the demulsifier was evaluated on artificial o/w emulsion and on-site ASP flooding produced liquid. The demulsification mechanism of o/w ASP flooding produced liquid was investigated through the tests including oil droplet coalesce, water phase viscosity, oil-water equilibrium interfacial tension, oil-water dynamic interfacial tension, oil droplet Zeta potential and oil-water interfacial rheology. The test results show that the o/w produced liquid of the ASP flooding project in Daqing Oilfield can be dehydrated at 45C with retention time and demulsifier dosage respectively at 3h and 150mg/L to reduce the water content of the crude oil effluent to below 0.5%; The demulsification mechanism of the o/w produced liquid is that demulsifier adsorbs on oil-water interface and removes some indigenous surfactants and injected surfactant from oil-water interface, reducing negative charge density on oil droplet surface and the repulsing force between two approaching oil droplets, which leads to oil droplet coalesce and o/w emulsion demulsification.


P 42

Encapsulation of Colloidal Materials within Liposomes

C. Evans, E. Kisak, C. Boyer, and J. Zasadzinski, Department of Chemical Engineering, University of California, Santa Barbara, CA 93106

Liposomes are spherical lipid bilayer membranes that surround an aqueous core. Their utility has been demonstrated for the delivery of anticancer and antifungal drugs within the body, and they are potentially useful for the encapsulation of colloidal particles. For example, an iron particle surrounded by a membrane containing an antigen or other targeting molecule could facilitate medical imaging or separations. Enclosure of DNA may provide a means of nonviral gene therapy. A general method of encapsulting such colloids is presented. When ethanol is added to certain phospholipid vesicles, the lipids interdigitate and sheets form. Removal of the ethanol and heating above the gel to liquid crystal transition cause reclosure of the sheets and afford micron-size vesicles that can enclose colloidal materials. This method of encapsulation has been investigated as a means of encapsulating DNA and cationic lipid / DNA complexes.


P 43

Critical Micelle Concentrations in Water and Organic Solvents: a Systematic Study

John Hagen and Gina McNamara, Chatham College, Woodland Road, Pittsburgh, PA 15232

Critical micelle concentrations (CMC) for cetyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TTAB), and dodecyltrimethylammonium bromide were determined in water, ethylene glycol, hexanol, and octanol using a fluorescence spectrophotometer. The effect of solvent structure and surfactant chain length on CMC is discussed in the context of the Klevens equation.


P 44

Photoresponsive Polymerized Crystalline Colloidal Arrays

Marta Kamenjicki, Igor K. Lednev, Sanford A. Asher, University of Pittsburgh, Department of Chemistry, 219 Parkman Ave., Pittsburgh, PA, 15260

Highly charged, monodisperse colloidal particles self-assemble into crystalline colloidal arrays (CCAs) in low ionic strength aqueous solutions. CCAs Bragg diffract ultraviolet, visible and near-infrared light. We recently developed a methodology to polymerize hydrogel networks around these CCAs to permanently lock in the ordering. These polymerized CCAs (PCCAs) may be used to develop new optical devices. We report on the development of a new type of a photoresponsive PCCA which can be used as a novel recordable and erasable memory device and/or display device. It can operate in either UV, visible or near IR spectral regions. The information is recorded using UV light and kept until visible light is used for erasing. This photoswitching material shows photochemically controllable shift in the diffracted light. This device was created by functionalizing a PCCA with azobenzene type molecules. Gradual red-shift of the diffraction peak upon UV illumination is accompanied by a decrease in p ® p * absorption, and an increase in n® p * absorption due to the trans ® cis isomerization of azobenzene. Excitation with visible light results in the reverse cis ® trans isomerization and a gradual diffraction peak blue-shift to the original position.


 

P 45

Role of the Interfacial Films on the Stability of Double Emulsion System (W1/O/W2)

Mouhcine Kanouni, Henri L. Rosano, The City College of the University of New-York, Department of Chemistry, Convent Avenue and 138th Street ,New York, NY 10031, USA

The stability and formation of a multiple emulsion had been intensively studied in our recent study. As a stability criteria for double emulsion, it was found necessary to balance the osmotic pressure with the Laplace Pressure in order to avoid Ostwald ripening. In addition, the physical-chemical properties of the surfactants at the interface O/W and the interaction of the surfactants dissolved in the aqueous phase were found to play a major role in the stability of the emulsions. The multiple emulsion has been prepared according to the methods described in our previous article. Among the different classes of primary surfactants (low HLB) tested, we found that cethyl dimethicone copolyol (Abil Em90), A-B-A block copolymer (Arlacel P135) allowed us to prepare a stable W1/O/W2 emulsion - over a 6 month period, at room temperature. Also, we investigated the primary interface for its proprieties using monolayer techniques. Results obtained show that in order to prepare a stable double emulsion, a reversible expandable and compressible film is necessary and it was also found that the film should be adsorbed irreversibly at the water/Oil interface.


P 46

Thiol-Based Polymerized Crystalline Colloidal Array Sensors

Jonathan P. Keim and Sanford A. Asher, University of Pittsburgh, Department of Chemistry, 219 Parkman Ave., Pittsburgh, PA 15260

PCCA sensors are a novel motif for sensitive and selective detection of a variety of analytes. Highly charged monodisperse polystyrene spheres form crystalline colloidal arrays (CCA) in low ionic strength solutions. The lattice spacing of these CCA causes these crystals to diffract visible light according to Braggs Law. These CCA are polymerized within an acrylamide hydrogel (PCCA) to lock the order of the crystal in place. Previous work has shown that PCCA can be modified to make sensors: lead responsive PCCA are made through inclusion of a crown ether comonomer, and glucose sensors are made by attachment of glucose oxidase to the PCCA. We have incorporated thiols into the PCCA to sense arsenic (III) oxide. N,Ncystaminebisacrylamide is used to crosslink these acrylamide PCCA. Dithiothreitol, a mild reducing agent, cleaves the disulfide bond within the crosslinker. Breaking the crosslinks swells the hydrogel and introduces two free thiol groups into the hydrogel. Pairs of thiols chelate arsenic (III) oxide. This chelation essentially forms crosslinks and decreases the gel volume, which in turn changes the spacing of the CCA. We monitor the diffracted wavelength which accurately tracks the decrease in gel volume, which can be used to determine the analyte concentration.


P 47

Extremely Stable W/O/W Multiple Emulsions by Manipulating Characteristics of Internal Water

Jin-Woong Kim, Byung-Guen Chae, Han-Kon Kim, and Hak-Hee Kang, Pacific Corporation R&D Center, Cosmetics Research Institute, Yongin-si, South Korea 449-900

Multiple emulsions provide many interesting potential possibilities for targeted and/or controlled release and encapsulation in cosmetic and pharmaceutical applications. There have been several approaches to produce stable multiple emulsions, such as the incorporation of systematic surfactant compositions, the treatment of phase properties, and the control of inter-diffusion behaviors. However, until recently, it has been a hard work to design a multiple emulsion system that satisfies the requirement in various applications. The main reason can be found in their intrinsic thermodynamic instability. Here in this study, we are proposing a useful approach that can obtain extremely stable W/O/W multiple emulsions. The basic concept starts from the hydrophobication of internal water, resulting consequently in the formation of highly stable internal water droplets. The hydrophobication of internal water was achieved by eliminating hydrogen bond between water molecules and clusterizing them macroscopically. In the present study, the long-term stability of W/O/W multiple emulsions is observed considering basically the characteristics of internal water. Continuously, the enhanced stability of water-soluble active materials is evaluated by encapsulating them in the multiple emulsions.


P 48

SANS and USANS Measurements of Micellar Gel Structure

Steven R. Kline, NIST Center for Neutron Research, 100 Bureau Drive, Stop 8562, Gaithersburg, MD 20899-8562

A crosslinked micellar gel has been prepared, consisting of a network structure of rodlike micelles. The gel is prepared by covalently crosslinking the polymerizable surfactant cetyltrimethylammonium 4-vinylbenzoate. The original viscoelastic solution of rodlike micelles is polymerized to form a covalently crosslinked space-filling gel. Thus, the material is effectively a "macro-micelle". Small Angle Neutron Scattering (SANS) and Ultra Small Angle (USANS) measurements of these gels over an extended q-range of (0.00005 to 0.5) A^-1 showed three distinct length scales. These length scales range from large static inhomogeneities (~ 600 nm) down to the micellar cross section of 4 nm. Solvent contrast variation measurements were used to determine the spatial distribution of the divinyl benzene crosslinker in the gel. In addition, the swelling or contraction of the gel in various organic solvents or salt solutions has also been investigated.


P48-A

Novel Amphiphilic Stimuli-Sensitive Hydrogels Based on Vinyl Ethers and Their Complexation with Linear Polymers and Surfactant

I.Nam1, K.D. Park1, Z. Nurkeeva2, G. Mun2, P. Urkimbaeva2, 1 Ajou University, Department of Molecular Science and Technology, 5 Wonchon, Paldal, Suwon 442-729, Korea, 2 Al-Faraby Kazakh State National University, Karasai Batyr Str., 95, Almaty 480012, Republic of Kazakhstan

Novel thermo-sensitive polymers were designed at a combination of hydrophilic and hydrophobic monomers at their mutual copolymerization. Vinyl ether of ethyleneglycol (VEEG), vinyl butyl ether (VBE), vinyl isobutyl ether (VIBE) were used as monomers. The linear copolymers VEEG-VBE, VEEG-VIBE and VEEG-VBE-AA show low critical solution temperature (LCST) in aqueous solutions. The cross-linked polymers exhibit thermo-induced collapse behavior. Parameters of their phase transition can be regulated by ionic strength of an environment as well as copolymers composition. The interactions of the hydrogels with linear polymers in aqueous solutions as well as with cetylipyridinium bromide were investigated. Effectiveness of the complexation can be regulated by pH, high ionic strength as well as ethanol-water mixed solvent composition. The swelling behavior depends on the properties of hydrogel-solution interface. In the number of cases the complex hydrogels swell much higher in water than initial networks and undergo dramatic collapse with temperature increase. Some of the modified networks exhibit complicated thermo-sensitivity with several extremes.


P 49

The Diffusive Interfacial Transport (DIT) Method for Characterizing the Phase Behavior of Surfactant and Water Mixtures

Kelly Kochvar and Matthew Lynch, Corporate Research Division, the Procter & Gamble Company, Miami Valley Laboratories, 11810 E. Miami River Road, Route 27, Cincinnati, Ohio, 45061.

Charting the phase behavior of surfactant and water mixtures in a methodical and thorough fashion has always been difficult. Traditional techniques are often laborious, time-consuming and unreliable. This poster presents a novel approach termed the Diffusive Interfacial Transport-Infrared Method (DIT-IR) which offers a significant improvement to phase study methods. It couples swelling methods, which simultaneously create all possible phases in a small capillary, with near-infrared spectroscopy to ascertain the entire phase diagram in one experiment. The method offers a methodical and thorough approach to defining the phase behavior of surfactant and water mixtures.


P 50

Effect of Cosurfactant on Phase Behavior in Systems Containing Nonionic Surfactant, Water, and Lubricant

SangSoo Bae, JongGi Lee,* *Central Research Lab., Aekyung Industrial Co., LTD., DaeJon 300-200, Korea, SangJoon Park, Department of Chemical Engineering, KyungWon University, SungNam 461-701, Korea, SangKwon Park, JongChoo Lim, Department of Chemical Engineering, Dongguk University, Seoul 100-715, Korea

In this work, the effects of cosurfactants on the phase behavior for systems containing commercial POE nonionic surfactant, water, and industrial lubricant were investigated as a function of surfactant concentration, temperature, and ratio of cosurfactant to surfactant. The results in the surfactant systems without any cosurfactant showed an oil-in-water microemulsion in equilibrium with excess oil phase at low temperatures and a water-in-oil microemulsion in equilibrium with excess water phase at high temperatures. For intermediate temperatures a narrow three-phase region containing water, oil, and middle-phase microemulsion was observed. On the other hand, phase behavior in the surfactant systems with addition of cosurfactant showed different trends depending on temperature and chain length of alcohol added. For example, addition of a long-chain alcohol such as n-heptanol lowered the temperature necessary for the formation of a three-phase region and produced a middle-phase microemulsion over a wide range of temperatures. Also addition of n-hetanol promoted the solubilization mainly due to a decrease in interfacial tension. Under the same experimental conditions, the addition of rather short-chain alcohol such as n-pentanol or n-hexanol did not produce a middle-phase microemulsion. Instead, the L3 phase was formed, which could not promote the solubilization of lubricant.


P 51

Stability and Inversion of Solid-Stabilized Emulsions

B. P. Binks1 and S. O. Lumsdon2, 1Surfactant Science Group, Department of Chemistry, University of Hull, Hull, HU6 7RX, U.K., 2Center for Molecular and Engineering Thermodynamics, Department of Chemical Engineering Colburn Laboratory, University of Delaware, Newark, DE 19716, U.S.A. (Work carried out at the University of Hull).

Emulsions can be stabilised by solid particles in the absence of surfactant. The contact angle which the particle makes with the oil-water interface is believed to be important in determining the type and stability of the emulsion. If the contact angle, measured through the water phase, is < 90, it is predicted that oil-in-water (o/w) emulsions are preferred, whereas if the contact angle is > 90 water-in-oil (w/o) emulsions are preferred. We have studied the formation and properties of emulsions stabilised by spherical silica particles alone (Wacker-Chemie, ~20 nm diameter). Starting from completely hydrophilic silica, we have obtained a range of particles which have been treated with an organosilane reagent to different extents rendering the particles increasingly hydrophobic. Upon increasing the hydrophobicity, emulsions prepared from equal volumes of water and toluene invert from o/w to w/o as expected. The stability depends markedly on the particle hydrophobicity. For a fixed particle hydrophobicity, catastrophic phase inversion of emulsions occurs upon increasing the volume fraction of dispersed phase in the system. Transitional phase inversion has been achieved by varying the weight fraction of hydrophilic (prefers o/w) and hydrophobic (prefers w/o) particles in a system of fixed volume fraction.


P 52

Some Block Copolymer Vesicles Are Thermodynamically Stable Structures

Laibin Luo and Adi Eisenberg, Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec, H3A 2K6, Canada

Vesicles prepared from polystyrene-b-poly(acrylic acid) (PS-b-PAA) diblock copolymers, in which the PS is incorporated in the hydrophobic wall and the PAA in the corona, can be thermodynamically stable structures in some solvent systems. The stabilization is achieved by preferential segregation of the hydrophilic blocks containing short poly(acrylic acid) chains to the inside of the vesicles and the long poly(acrylic acid) chains to the outside. The repulsion among the longer chains is stronger than that among the shorter chains, which stabilizes the curvature of the vesicles. This mechanism was proven by fluorescence quenching measurements on vesicles containing small amounts of fluorescently labeled block copolymers of a constant polystyrene length, with a fluorophore at the junction, and containing blocks of varying poly(acrylic acid) lengths. This finding allows us to design system in which various species can be placed preferentially either on the inside or on the outside vesicle wall, or two different species one inside and one outside, which could be useful in various applications.


P 53

Amphiphilic Block Copolymer Spherical Micelles in Water: Model Objects of Controlled Interface Curvature and Chain Surface Density

Denis Bendejacq, Virginie Ponsinet, Mathieu Joanicot, CNRS-Rhodia, Complex Fluids Laboratory, 259 Prospect Plains Road, Cranbury, NJ 08512, USA, Jyotsana Lal, IPNS, Argonne National Laboratories, 9700 S. Cass Avenue, Argonne, IL 60439, USA

Amphiphilic diblock copolymers of poly(styrene-b-acrylic acid) are studied at equilibrium in the dilute regime in water, for various diblock compositions at constant overall molecular weight (16 kg/mol). The hydrophobic block is always kept as the minority component. Small-angle Neutron scattering experiments show that these copolymers self-assemble into spherical micelles, also visualized by transmission electron microscopy. They comprise a collapsed polystyrene hydrophobic core, glassy at room temperature, surrounded by a swollen polyelectrolyte brush. The core radius and the aggregation number are both found to increase as power laws of the length of the PS block, whereas the chain surface density is found to decrease. These experimental observations suggest the existence of a crossover in the balance between the free energies of the surface tension and both block conformations, when the composition of the diblock is varied. This balance controls the curvature and the density of the brush. We study how the crossover can be tuned by playing with the brush conformation free energy term, through the ionization degree of the polyelectrolyte. We will finally show that the brush density determines the behavior of the system when concentrated above its gel point.


P 54

Development of a Colorimetric Reagent Using Intelligent Polymerized Crystalline Colloidal Arrays

Chad E. Reese, Michael E. Baltusavich, Jonathan P. Keim, Sanford A. Asher, University of Pittsburgh 219 Parkman Avenue Pittsburgh , PA 15260

We have developed a dispersion of chemical sensing particles that serves as a colorimetric reagent for the determination of temperature, pH, and Pb2+. These chemical sensing particles are fragments of polymerized crystalline colloidal arrays (PCCA, 100 m m 1mm in size) dispersed within an aqueous solution. PCCA are composed of monodisperse, highly charged polystyrene colloidal particles between 100 and 700 nm in diameter that form an fcc or bcc crystal structure which is polymerized within a hydrogel network. The spacing in the crystal is such that it Bragg diffracts visible light. When the gel particles undergo volume phase transitions and shrink or swell in response to environmental changes, the spacing in the crystal changes which shifts the wavelength of light diffracted. This sensing material can be poured as an analytical reagent into a sample solution and be monitored via the human eye or a cheap spectrophotometer.


P 55

Solubilization and Release of Hydrophobic Probes from Biocompatible

Polycaprolactone-b-poly(ethylene oxide) Block Copolymer Micelles

Patrick Lim Soo, and Adi Eisenberg, Department of Chemistry, Dusica Maysinger, Department of Pharmacology and Therapeutics, McGill University, 801 Sherbrooke St. W., Montreal, Quebec, Canada, H3A 2K6

Within the past few years a considerable amount of research has been devoted to exploring the use of amphiphilic block copolymers micelles as drug delivery vehicles. The potential application of these micellar aggregates as drug carriers depends on their ability to solubilize small, hydrophobic molecules within their inner core and to provide slow release of these compounds. The biocompatible copolymer polycaprolactone-b-poly(ethylene)oxide (PCl21-b-PEO44) is an effective drug delivery vehicle for FK506 and dihydrotestosterone (DHT) (refer to Bioconj. Chem., 9, 1998, 564 and BBA, 1421, 1999, 32). Fundamental knowledge about the nature of the solubilization of hydrophobic molecules in the PCl21-b-PEO44 micelles and the release of these compounds from the aggregates is not well known. In an attempt to understand these phenomena, loading and release studies were carried out using two hydrophobic fluorophores, benzo[a ]pyrene and CM-DiI, and PCl21-b-PEO44 micelles. The loading and release process, as well as the partition coefficients were determined for each fluorophore using fluorescence spectroscopy. The results from these studies have shown that the micelles can incorporate a greater amount of CM-DiI than benzo[a ]pyrene and that there is a delayed and controlled release of both probes from the PCl21-b-PEO44 micelles.


P 56

Influence of the System Parameters on the Formation of Capillary Alginate Gels

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

When a solution of the polyelectrolyte alginate is brought into contact with a solution of divalent copper ions, the copper ions will diffuse into the alginate sol and cross-link the alginate chains. Under appropriate conditions, the gel body thus formed will show a section with a regular capillary structure. Structuring is caused by the chemical fixation of a hexagonal pattern of torus-shaped convection cells forming in front of the gel body [ 1] . Convection is due to frictional forces produced by the contraction of the chain molecules during the transition from the sol to the gel state. Above a certain threshold this leads to convective circulation of the fluid. The critical contraction velocity depends on the migration velocity of the gel front, the diffusive and convective material transport of alginate and copper towards the gel front, and the thickness of the contraction zone [2]. In this contribution, the latter component is considered in detail. A theoretical model is presented and compared with experimental results.

[1] J. Thumbs, H.-H. Kohler, Chem. Phys. 208 (1996) 9-24.

[2] H. J. Treml, H.-H. Kohler, Chem. Phys. 252 (2000) 199-208.


P 57

Synthesis of Charged Polystyrene for Crystalline Colloids Array

Ying Wang and Sanford A. Asher, Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260

Highly charged monodisperse colloidal particles will self assemble into a highly ordered three-dimensional array, crystalline colloidal array, in solution, if the average particle spacing is much greater than the particle diameter. This self assembly occurs due to the repulsion between particles which causes the array to be the lowest energy state of the colloidal dispersion. In this study, we use in situ seeding technique to prepare sulfonated polystyrene particles. Stable, monodisperse core polystyrene particles with the controllable size can be prepared by the emulsion polymerization. Introducing the mixture of styrene, Cops-I (ionic comonomer, sodium 1-allyoxy 2-hydroxypropane sulfonate) and additional initiator at the end of polymerization, the surface charge density of the final particles can be changed depending on the ratio of Cops-I in the monomer mixture. After dialysis, all samples diffract light in the visible regions.


P 58

Phase Behavior and Microstructure of Food Grade Microemulsions Based on Nonionic Emulsifiers

A. Yaghmura, A. Aserina, M.E. Leserb, V. Clementb and N. Gartia, aCasali Institute of Applied Chemistry, The Hebrew University of Jerusalem 91904, Israel, bDepartment of Food Science & Technology, Nestle Research Center, Nestec Ltd., Vers-chez-les-Blanc, 1000, Lausanne 26, Switzerland

The phase behavior of the system of R(+)-limonene, ethanol, water/propylene glycol (1/1) and polyoxyethylene sorbitan monostearate (Tween 60) containing a 1:1:3 R(+)-limonene:ethanol:surfactant weight ratio is characterized by a single continuous microemulsion region starting from a solution containing pseudo binary (surfactant/oil phase) to the microemulsion water/propylene glycol (1/1) corner. Such systems are suitable for food applications. Along this dilution line, NMR self-diffusion, viscosity, and conductivity measurements indicate that at certain composition the system inverts from W/O to O/W microemulsion. The temperature insensitive microemulsion systems have been studied using cryo-transmission electron microscopy (cryo-TEM), and small angle X-ray (SAXS), and neutron scattering (SANS). It seems that the ethanol penetrates into the surfactant interface and acts as a cosurfactant , while it appears that PG behaves as a cosolvent and acts to change the polarity of the water. The maximum water and/or oil solubilization was evaluated. The influence of water-soluble alcohols (glycerol, propylene glycol) incorporated as polar cosolvent on the phase behavior and the microstructure of a these food microemulsion has been investigated. Polar organics like propylene glycol, and glycerol may affect the spontaneous curvature, H0, of the surfactant film in different ways, either by being incorporated in the surfactant film, which increase the flexibility of the surfactant film, destabilizing the lamellar phase that is formed without these alcohols, or by changing the polarity of the polar phase.


P 58-A

Investigation of the Fundamental Mechanisms of Ostwald and Compositional Ripening in Oil-in-Water Emulsion Systems

Sachin S. Vaidya, Ari Gajraj, Robert Y. Ofoli, Department of Chemical Engineering, Michigan State University, East Lansing, MI  48824

Oil-in-water emulsions (EWs) can form the basis of several commercially important products. They are environmentally safe alternatives to emulsifiable concentrates (ECs). However, EWs are generally thermodynamically unstable and suffer from shelf-life problems. The primary causes of instability of EWs are coalescence and Ostwald ripening. Another process that has been recently exploited to improve EWs is compositional ripening. Despite the fact that there have been many studies of these phenomena in the past few years, the mechanism and the role of surfactants and/or surfactant micelles in the two ripening processes are still unclear. We present results of total internal reflection microscopy (TIRM) at the oil-water interface to study the interactions of a single oil droplet with a planar oil-water interface. Light scattered by the droplet in the evanescent wave was used to determine the potential energy of interaction between the two bodies and the size of the droplet, both as a function of time. By varying the composition of the oil layer, the size and concentration of the oil droplet, and the type and concentration of surfactants in the system, we obtained information about the effect of these parameters on the time-dependent size of the droplet.


P 59

Thixotropic Properties of Aqueous Dispersions of Positively Charged Al/Mg Mixed Hydroxides

Dejun Sun, Wanguo Hou, Chunguang Zhang, Shandong University, Key Laboratory for Colloid and Interface Chemistry of the Ministry of Education, Jinan 250100, P. R. China

The rheological properties of aqueous dispersions of the Al-Mg mixed metal hydroxide (MMH) have been investigated. Special emphasis has been laid on the phenomenon of thixotropy. Structural recovery at rest after steady shear is considered a fundamental thixotropic process and has been characterized by small amplitude oscillatory shear measurements. It was found that, the complex viscosity of MMH suspensions increases monotonically with time after cessation of pre-shear, and no equilibrium viscosity value is reached even over 3 hours. The recovery of MMH suspension after cessation of steady shear is strongly affected by pre-shear history and rebuilding time. The greater the intensity of preshearing, the lower the values of the elastic moduli after preshearing has ceased; the longer the rebuilding time, the larger the values of the elastic moduli. These results are similar to those obtained for clay dispersions of different ionic strengths and clay concentrations. The similar phenomenally macroscopic thixotropic properties between the two particulate systems of oppositely charged particles provide indirect evidence of similar rebuilding mechanism for suspension structure.


P 60

Rheological Properties of the Clay Dispersion with the Terpolymer of N-Vinyl Pyrrolidone-Acrylamide-Itaconic Acid

Yumin Wu, Dejun Sun, Tao Wu, and Chunguang Zhang, Key Laboratory for Colloid and Interface Chemistry of the Ministry of Education, Shandong University, Jinan 250100, P. R. China

The terpolymer of N-vinyl pyrrolidone, acrylamide and itaconic acid is synthesized through the free-radical polymerization, and characterized using FTIR. Rheological properties of the clay dispersion are modified by the terpolymer in fresh water before and after the aging tests at 220° C. The apparent viscosity and the plastic viscosity of the dispersion increase slowly and regularly with the increase of terpolymer concentration before and after aging tests, while the yield point presents the same trends as the viscosities before the aging test and gets zero value after the aging test. The terpolymer-clay system displays positive thixotropy before and after aging tests. The particle size distribution data demonstrate that the average size of the clay particle changes very little before and after the aging test, and this further confirms that the terpolymer is an excellent rheology modifier at high temperature from another point of view.


P 61

Rheology and Colloidal Properties of the Montmorillonite Suspension with the Terpolymer of Acrylamide-N,N-Dimethylacrylamide-2-Acrylamido-2-Methyl-1-Propane Sulfonic Acid at High Temperature

Yumin Wu, Dejun Sun, Baoqing Zhang and Chunguang Zhang, Key Laboratory for Colloid and Interface Chemistry of the Ministry of Education, Shandong University, Jinan 250100, P. R. China

The terpolymer of acrylamide, N,N-dimethylacrylamide and 2-acrylamido-2-methyl-1-propane sulphonic acid is synthesized. An experimental investigation is undertaken into the rheology and colloidal properties of the terpolymer-montmorillonite suspension. The water-loss volume reduces with the increase of the terpolymer concentration before or after the aging test at 240° C. A little variation of the clay particle size occurrs before and after aging tests, this confirms the thermal stability of the terpolymer-clay suspension. The rheology properties of the clay suspension are improved by the terpolymer. The apparent viscosity, the plastic viscosity and the yield point of the clay suspension increase with the increase of terpolymer concentration in fresh water, while these viscosities give minimum values with the increase of terpolymer concentration in salt water. Clay particles in water are attracted to each other to build up a gel structure with viscosity and strength through attraction and repulsion of the electric double layer according to DLVO theory.


P61-A

Electrokinetic and viscoelastic properties of core-swelling-shell colloidal dispersions

G. Fritz, V. Schädler, N. J. Wagner, N. Willenbacher, Department of Chemical Engineering, University of Delaware, Newark, DE 19716

Dispersions consisting of a polybutyl acrylate polystyrene core with polymethacrylic acid (PMAA) chains grafted to the surface were studied to quantify the steric stabilization induced by the PMAA layer. Different pH values allow changing the degree of dissociation of the acid groups of the PMAA chains and thereby the layer thickness can be varied. The PMMA layer enhances the stability of the dispersion considerably even at low pH values when it is mostly collapsed. Dilute solutions are studied using DLS and electrophoretic mobility measurements to determine the swelling of the layer and the zeta potential, respectively. High volume fractions are investigated with classical and high frequency rheology (w: 23000-360000 s-1). Special interest is paid to volume fraction dependence of the high frequency elastic modulus (G') to probe the interaction potential and to the frequency dependence of G'. The measured rheology and dynamics in the concentrated dispersions are related to the measurements of the electrosteric forces inferred from the dilute solution measurements.


P 62

WITHDRAWN.


P 63

Atomic-Scale Modification of Gold Surfaces to Affect the Surface-Catalyzed Formation of Polymethylene Films

G. Kane Jennings and Wenfeng Guo, Vanderbilt University, Department of Chemical Engineering, Box 1604 Station B, Nashville, TN 37235

Highly crystalline polymethylene [-(CH2)n-; PM] films with thicknesses up to 100 nm form onto gold surfaces that are immersed into a dilute ether solution containing diazomethane. Modification of the gold surface with underpotentially deposited (upd) metal monolayers provides a convenient strategy for tailoring the metal surface chemistry and altering the kinetics of polymer growth and the properties of the surface-catalyzed polymethylene films. While the kinetics of PM film growth from unmodified gold are consistent with a free-radical mechanism, those of PM grown from Cu upd-modified gold are consistent with a living polymerization in which the polymer film growth is linear with time. As shown by atomic force microscopy (AFM), the morphology of the PM films depends on the atomic-level composition and coverage of the metal surface. The underpotential deposition of silver poisons the catalytic effect of the gold surface while the upd of copper or palladium enhances the growth of the polymer over that of unmodified gold. The level of enhancement depends on the coverage of the upd metal, which is easily controlled through cyclic voltammetry, and its interaction with the adsorbed methylidene species that initiates the polymerization reaction


P 64

WITHDRAWN.


P 65

WITHDRAWN.


P 66

Electrochemical Control of Surface Potential in the Surface Forces Apparatus

Joelle Frechette and T. Kyle Vanderlick, Chemical Engineering Princeton University, A214 Equad Princeton, NJ,08544

Measurements of forces between a gold electrode and mica were carried out with the surface forces apparatus (SFA). Control of the gold surface potential was achieved by soldering a wire to the gold surface and modifying the chamber of the SFA into a three-electrode cell configuration. Interactions between the gold electrode and mica were probed in a series of force measurements done at different potentials. The interactions were a strong function of the electrode potential, being more repulsive as the gold potential was moved towards more negative potentials. Independent force measurements between mica surfaces were done to determine the mica surface potential. The experimental results were then compared to theoretical predictions of the forces between dissimilar charged surfaces obtained by solving the complete non-linear Poisson-Boltzmann equation.


P 67

Macroscopic Model System for Self-Assembly in Confined Spaces

Michael Hay, Rick Workman, Srinivas Manne, Department of Physics, University of Arizona, Tucson, AZ 85721

A chief obstacle in the study of colloidal behavior is the lack of simple macroscopic models with well-defined and tunable interactions. We have designed a model consisting of superparamagnetic chrome steel spheres on a level surface, exposed to an external magnetic field perpendicular to the horizontal plane. Magnetic dipole fields are induced in the spheres, which causes them to repel one another. Not only is the dipole-dipole repulsive force well understood theoretically, it can also be varied externally by adjusting the field strength, providing a well-controlled model. Using this system, we demonstrate solid/liquid phase transitions, adsorption phenomena, epitaxial ordering, and stratified thinning. Many experimental measurements compare favorably to theoretical analyses using the known dipole-dipole interaction potential.


P 68

Structure and Dynamics of 1 nm Wide PEO/Li+ Films Confined in Slit Pores

V. Kuppa, E. Manias Materials Science & Engineering Department, Pennsylvania State University, University Park, PA 16802

Molecular Dynamics computer simulations are used to explore the structure and dynamics of poly(ethylene-oxide) confined in an 1-nm slit. The systems simulated resemble experimentally studied intercalated nanocomposites, where PEO is inserted between 2:1 silicate layers (synthetic, mica-type, or clays). The molecular modeling perspective complements previous NMR experimental findings and provides insight into the nature of PEO and Li+ in nanoscopic confinements, especially into the molecular origins of their macroscopic behavior. Namely, in accord with the experiments, simulations show a distribution of polymer relaxations, ranging from extremely faster and to much slower segmental motions than the ones found in the corresponding bulk polymer at the same temperature. At the same time, the Li+ mobility, which is connected to the cationic conductivity of the system, undergoes no qualitative change as the temperature is decreased below the bulk Tg. Simulation acquired insights will be provided, and a comparison with NMR experiments will be made.


P 69

Crystallization Patterns from an Evaporating Drop

P. Takhistov and University of Notre Dame, Notre Dame, IN 46556, University of Notre Dame, Notre Dame, IN 46556

A rich spectrum of crystal patterns are observed when a drop of ionic or protein solution evaporates on a solid substrate. Other than the well-known crystal fingers from homogeneous crystallization, heterogeneous crystallization at the contact line produces stripe and fractal patterns at much smaller length scales between 20 and 200 microns. Such patterns are shown to result from interplay among crystallization, contact-line motion, non-uniform evaporation and diffusion within the precursor films of wetting drops. Universal correlations among pattern length scale, bulk concentration and crystal size are established and explained theoretically.

Heterogeneous crystallization is also shown to modify the contact-line dynamics to produce macroscopic stain topologies like circles, bands, crescents, stars etc.


P 69-A

Spreading and Wetting on Heterogeneous Substrates: What Do We Learn from Simple but Large-Scale Molecular Dynamics Simulations?

M. Voué and J. De Coninck, University of Mons-Hainaut, Research Centre for Molecular Modelling, place du Parc, 20, B-7000, Mons (Belgium)

In the modern approaches to wettability, the spreading phenomenon of a liquid droplet on a solid surface is understood as the consequence of a competitive process between a driving term and the friction of the liquid molecules on the solid surface. This driving term is either the out-of-balance force in the partial wetting regime, as given by the difference between the time-dependent and the equilibrium contact angles of the droplet on the substrate, or the affinity of the liquid molecules for the substrate, in the complete wetting regime. These concepts are now widely accepted, when concerning pure liquids spreading on pure substrates. We present in this communication their extension to the case of heterogeneous substrates. These extensions are supported by large-scale molecular dynamics simulation results, as well as by experimental ones.


P 70

Effect of Composition on Surface Free Energy of Acrylic Latex Film

SeungWhan Song, JongMyong Park*, SangJoon Park**, JongChoo Lim, Sangkwon Park Department of Chemical Engineering, Dongguk University, Seoul 100-715, Korea
*Central Research Lab., Korea Chemical Co., LTD., YongIn-Si, Kyunggi-Do 449-910, Korea
**Department of Chemical Engineering, Kyungwon University, SungNam 461-701, Korea

Recently, there has been a growing interest in waterborne coatings mainly because they are environmentally friendly. The requirements of waterborne coatings to protect building materials include low water absorption and dirt pick-up, which are closely related to their surface free energy. In this work, the effect of monomer composition on the surface free energy of acrylic latex films was investigated by measuring the contact angles of water and methylene iodide at the air/film interface and of octane at the water/film interface. Nine latex dispersions were prepared by emulsion-polymerization of the mixture of a main monomer, an auxiliary monomer and methacrylic acid. Ethylacrylate (EA), butylacrylate (BA) and 2-ethylhexylacrylate (EHA) were used as the main monomers and acrylonitrile (AN), methymethacrylate (MMA) and styrene (St) as the auxiliary monomers. The latex films were casted by dring the corresponding dispersions. The contact angle of octane was in the order of EA>BA>EHA for MMA and St whereas in the reverse order for AN. As the results of contact angles of water and methylene iodide, the latex films containing EA showed the largest polar component of surface free energy. These trends were supported by the electron spectroscopy for chemical analysis (ESCA) results of the latex films.


P 71

Preparation of Poly(D,L-Lactic-co-Glycolic Acid)(PLGA) Nanoparticles by Solvent Evaporation Method

Sang Joon Park, Tae-Seung Song, Department of Chemical Engineering, Kyungwon University, Seongnam City, 461-701, Korea, Jong-Choo Lim, Sang-Kwon Park, Department of Chemical Engineering, Dongguk University, Seoul, 100-715, Korea*

The preparation of biodegradable nanoparticles as an colloidal carrier system for water insoluble model drug was investigated. Sudan Black B(SBB) was used as model drug. For the economic production of drug delivery systems, the simple solvent evaporation technique has been employed and evaluated. The experiments were performed using three biodegradable polymers, poly[D,L-lactic-co-glycolic acid](PLGA) which have different mol ratios of lactic acid to glycolic acid, i.e., 50/50 , 75/25, and 85/15. As solvents, aceton and aceton/alcohol were used and polyvinyl alcohol(PVA) was utilized as stabilizer. As a process parameter, the PVA concentration was examined to achieve the optimum preparation conditions. In addition, the yield, particle size, size distribution and in vitro drug release property of the PLGA nanoparticles were evaluated. It was found that the simple solvent evaporation method can be used to provide PLGA nanoparticles of satisfactory quality. In addition, in this presentation, the release properties of SBB for different polymers and the effect of polymer compositions on the release profile will be reported and discussed.


P 72

Optical Characterization of Thin Colloidal Films Grown in Electric and Magnetic Fields

E.S. Kooij, E.A.M. Brouwer, H. Wormeester, B. Poelsema, Department of Applied Physics, MESA+ Research Institute, University of Twente, P.O. Box 217, NL-7500AE Enschede, The Netherlands

Thin films and ordered assemblies of nanometer-sized particles can be grown using a variety of techniques. Hydrodynamic forces during (controlled) drying, gravity and/or chemical modifications of the substrate have a profound influence on the growth of colloidal structures. Better control of layer growth can be achieved by electrophoretic deposition, an established technique for depositing charged colloidal particles onto electrodes. This technique relies on the motion of charged particles under the influence of an electric field. Similarly, magnetic fields can be employed to direct particles onto a substrate thereby making use of the motion of magnetic particles in magnetic field gradients. We investigate to what extent the aforementioned external fields can be used during or after the deposition process to control or modify the structural and physical properties of colloidal thin films. Both in situ and ex situ reflectometry and spectroscopic ellipsometry are employed to study the deposition and self-organization of these colloidal films. The optical experiments are complemented by scanning probe microscopy (AFM) and electron microscopy (TEM/SEM) measurements.


P 73

Effects of Nucleation and Growth on the Microporosity, Crystallinity and Morphology of Nanoparticle Single Crystals

Syed Ali Shah, Charles F. Zukoski, Department of Chemical Engineering, University of Illinois at Urbana-Champaign, RAL, Box C-3, 600 S. Mathews Ave., Urbana, IL - 61801, USA

Heteropolyanion salts possess ideal catalytic properties that are believed to inherently rely on the nucleation and growth mechanism of the colloidal particles during synthesis. The microporosity of these materials has been attributed to the nucleation of 10-20 nm nanocrystals that systematically aggregate into a close packed structure forming interstitial voids. Evidence for this growth mechanism is based on electron micrographs and limited atomic force microscope studies that provide little information about the mechanism of assembly or how to control the size of the growth units. Our studies show that the final porosity of the crystals can be varied over a factor of two, by changing the growth conditions indicating that there is scope for further engineering these materials. Dynamic light scattering is employed to determine particle size distributions of both initial nuclei and the succeeding nanoparticle crystals. Conductivity and scattered light intensity measurements revealed well defined induction periods that precede nucleation and growth. The induction period and subsequent growth rates have been measured as functions of reactant concentrations and the presence of background NaCl. These studies reveal that the induction period is slowed by the presence of background electrolyte. Powder X-ray diffraction patterns taken on dried (NH4)3PW12O40 synthesized at a variety of temperatures reveals a bcc structure that is independent of solution conditions during the precipitation. Electron diffraction patterns show that the particles maintain their crystalline structure throughout the growth process and N2 adsorption studies reveal the particles can attain surface areas in excess of 170 m2/g. In this paper, a comprehensive study of the kinetic and thermodynamic factors that affect the growth rates, morphology and microporosity is presented and the proposed aggregative growth model is critically evaluated.


P 74

Nanostructured Gold Films Templated by Colloidal Crystals: Application to Surface-Enhanced Raman Spectroscopy

Peter M. Tessier, Orlin D. Velev, Abraham M. Lenhoff, Eric W. Kaler, Department of Chemical Engineering, University of Delaware, Newark, DE 19716, Anand Kalambur, John F. Rabolt Department of Materials Science and Engineering, University of Delaware, Newark, DE 19716, Kate K. Ong, Steven D. Christesen, Edgewood Chemical and Biological Center, US Army SBCCOM , Gunpowder, MD 21010

We previously introduced a novel approach for the formation of nanostructured materials using colloidal crystals from submicrometer spheres as templates (Nature, 389:447, 1997). The particle arrays are embedded in a matrix that preserves the long-ranged ordered structure. Recently we have applied the method to the formation of porous metallic gold structures (Nature, 401:548, 1999). The 3D metallic structure is assembled from nanometer-size gold particles that fill the interstices in the latex crystal, which imparts a second level of porosity to the films. The assembly scheme has now been extended to the deposition of structured metallic films on glass supports using both silver and gold nanoparticles, which are only one or two layers of latex particles thick. These supported porous films are semi-transparent, colored, and show interesting transmission properties due to the cooperative effects of the ordered structure and the surface plasmon resonance. We have evaluated these nanostructured films as substrates for surface-enhanced Raman spectroscopy (SERS), which show excellent sensitivity and stability (JACS, 122:9554, 2000), including the detection of ppb levels of sodium cyanide and sub-ppb levels of trans-1,2-bis(4-pyridyl)ethylene. We have also studied the effect of the size of both the metallic and latex particles on the Raman enhancement.


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