The Dynamics of Phase Inversion

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9421580 McHugh, Anthony Phase inversion refers to the process by which a concentrated polymer solution is converted into a solid gel network with desirable, end-use properties. This process plays a central role in a number of polymer material fabrication technologies, the most important of which is membrane formation. The long-range goal of this research iq to advance the fundamental understanding of the generic, dynamic aspects of phase inversion, and, thereby, provide a more quantitative basis for its application in the development of new materials. The proposed work is an experimentally-based study which capitalizes on unique methodologies recently developed in the P.I.'s laboratory for in-situ observation of the diffusion and gelation dynamics which occur when a polymer solution is contacted with a nonsolvent medium. In-situ visualization techniques will be used to monitor the crystallization, macroscopic, homogeneous diffusion, gel growth, interfacial structuring kinetics, and bath-side mass transfer processes which take place in nonsolvent-quenched films. Dynamic small-angle scattering experiments will also be carried out on thermally-quenched solutions to gain new information on the interplay of the various phase separation processes (liquid-liquid phase separation - by spinodal decomposition or nucleation and growth mechanisms, glass transition, and physical gelation) which control the kinetics of formation and morphology of the phase-separated, gel structure. The nonsolvent-quenching experiments will be analyzed in terms of phenomenological models for the diffusion and gelation processes. In the latter case, analysis of the effects of non-equilibrium at the film-bath interface will be carried out to quantify the conditions under which spilodal decomposition, vitrification, and/or nucleation and growth phenomena may be involved in the gelation, and, structure formation processes. Systems to be studied will include amorphous and crystallizable polymers in solvent/nonsolvent co mbinations corresponding to rapid and delayed precipitation quench conditions. Morphological studies of the formed structures will also be carried out using electron microscopy. The experimental and modeling studies of this project will provide important, new information on the structure formation behavior of quenched polymer solutions. It is expected that the results will have a direct carryover in the prediction and control of the processing conditions necessary for the formation of gas separation reverse osmosis and ultrafiltration membranes.