Phase Separation and Interfaces of Confined Aqueous Colloidal Systems

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ABSTRACT CTS-9700147 Robert Marc/Rice U. It is proposed to study the phase separation, tension and structure of interfaces of confines aqueous colloidal systems. Confined colloid systems play important roles in several technological applications, such as paper, pesticides, cosmetics, pharmaceuticals, the processing of materials from ceramic powders, and the formulation of coatings (paints) for wood and masonry (brick, concrete, cement, stone, stucco). The study of aqueous colloidal systems is motivated by current stringent environmental and safety laws enforcing, in particular, the reduction or elimination of VOC (volatile organic compounds). In the project, emphasis is given to technologically important aqueous formulations such as those containing the nonionic water-soluble polymer HEC (cellulose ether hydroxyethylcellulose) and its hydrophobically modified from HMHEC specifically designed for aqueous dispersions. HEC and HMHEC are the most widely used thickeners/stabilizers in latex paints and essential additives in numerous materials such as inks, cosmetics, pharmaceuticals, foods, and ceramics. The systems to be studied are aqueous colloidal suspensions stabilized by non-adsorbing, water-soluble polymers. Phase separation (reversible flocculation) is investigated for confined systems as a function of composition and particle/polymer size ratio, and experimental results are compared with predictions of statistical mechanics. For confined systems, the interfacial structure, i.e., the variation of the colloidal concentration and the pair distribution (correlation) function in the interfacial region, are determined by digital videomicroscopy. These experimentally determined interfacial structures will be compared to those predicted by statistical mechanics. The tensions of the fluid interfaces will be determined for confined and unconfined colloidal systems, by the capillary rise and sessile drop methods and by digital videomicroscopy, in the latter case from the shape of the meniscus away from the sample cells walls. Together with its potential beneficial impact on energy and environmental issues, this research, if successful, will contribute to the advancement of knowledge by providing for the first time the determination of fluid phase separation of colloidal systems in confined geometries, the determination of interfacial tension of confined and unconfined colloidal systems, as well as the experimental determinations of interfacial structure and of critical interfacial tension of a confined, two-dimensional fluid. ***