9626828 Johnston The objectives are (1) to combine experiment and theory to provide a fundamental understanding of the effects of surfactants on interfacial properties in systems containing compresses carbon dioxide, and (2) to use these surfactants as steric stabilizers to form uniformly sized polymer microparticles and microfibers by precipitation into carbon dioxide. Carbon dioxide is an environmentally benign solvent that is being used to replace organic solvents for waste minimization. In future materials formation and heterogeneous polymerization processes, surfactants will play an important role. Because Co2 has very different properties than either hydrophilic or lipophilic solvents, innovative new types of surfactants will be required. The interfacial tension between liquids and carbon dioxide, and the adsorption of surfactants at these interfaces, will be measured with a novel tandem variable-volume tensionmeter for the first time and also calculated with a new lattice fluid self-consistent field model. The experimental studies and the model will be used to design polymeric surfactants at the molecular level to stabilize the interface between Co2 and liquids of varying polarity including water, and oligomers of poly(ethylene glycol), polyacrylates and polystyrene. The solvation of polymer chains by supercritical fluids will be studied by Monte Carlo computer simulation. Specifically, the transition from solvated chains to collapsed chains with the approach to a lower critical solution temperature phase boundary will be determined. The above fundamental knowledge will be used to design surfactants to produce polymeric materials by precipitation into liquid and supercritical fluid carbon dioxide. Here, a polymer solution is sprayed through a capillary into CO2 to precipitate microparticles, microspheres, and microfibers, with dimensions as small as 100nm. The surfactant will sterically stabilize the precipitating polymer microstructure to minimize flocculation and agg lomeration, which is often a major limitation in the current technology. Interfacial properties play a key role in materials formation processes and heterogeneous polymerizations. Surfactant adsorption has not yet been addresses for CO2 soluble surfactants. The interfacial tension and adsorption influence many phenomena including nucleation, growth, stability and coalescence of dispersed phases, atomization of sprays, and fiber formation from sprays. A knowledge of surfactant adsorption at CO2 liquid interfaces will be high beneficial to both fundamental studies of these phenomena and the development of new materials formation and polymerization processes. ***
