GOALI: The Dynamics of Phase Inversion

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CTS-9731509 Anthony McHugh U. of Illinois Studies are proposed of phase inversion, the process by which a cast polymer solution is converted into a porous, polymer gel by either thermal or nonsolvent quenching. Pore size and pore size distribution in the solidified polymer render properties favorable for membrane applications. Such membranes are ubiquitous in the separations and biomedical industries, having an annual commercial basis in excess of $1.6 billion. Hence understanding and controlling the conditions for their optimal fabrication has technological and scientific importance. Experimental and modeling analyses will be directed towards fundamental understanding of the dynamics by which membrane structures are formed and locked-in during quenching. Experiments will utilize a combination of in-situ measurements techniques based on dark-ground microscopy and small angle light scattering, coupled with video imaging. These provide unique quantitative data on the diffusion and liquid-liquid phase separation kinetics associated with phase inversion, as well as the freezing in of gel structure by glass transition or crystallization. Microstructural analysis of the formed morphologies will be carried out using electron microscopy. Quenching experiments will involve a number of polymer/solvent/nonsolvent systems, including crystallizable and amorphous polymers. Data will be analyzed in terms of mathematical models based o spinodal decomposition coupled with external mass transfer. The goal of modeling will be to quantify the mechanisms by which finger-like or spongy porous structures form during liquid-liquid phase separation and are then frozen in. In-situ techniques will also be applied to study phase inversion phenomena related to the in-vivo formation of controlled release drug delivery membranes, an area of growing importance in the biomedical and pharmaceutical industries. Membrane formation dynamics will be monitored in the biodegradable copolymer, poly (lactic-co-glycol ic acid) PLGA, dissolved in various nontoxic solvents, and quenched in water. The simultanoeus release characteristics of a model protein, lysozyme, from the as-formed membranes will also be determined. The objective will be to quantify relations among solvent water solubility, system glass-forming characteristics, and the formation of membrane structure favorable for simultaneous, in-situ encapsulation and controlled release of protein. Results of these studies will have direct application in the field of controlled drug delivery. ***