The Dynamics of Phase Separation and Structure Formation in Phase Inversion

137 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1998.Studies of phase inversion are presented, the process by which a cast polymer solution is converted into a porous, polymer gel by either thermal or nonsolvent quenching. In all three of the studies presented in this thesis, in-situ optical techniques have been used to study the dynamics of phase separation and morphology development that occur during phase inversion of polymer solutions. The first two studies employ small angle light scattering to quantify the kinetics of two-phase domain growth that occurs during thermally-induced phase separation of a binary (polymer/poor solvent) system based on a crystallizable polymer and a ternary (polymer/solvent/nonsolvent) system based on an amorphous polymer. Measurements made on solutions consisting of a crystallizable polyethylene copolymer (polyethylene-co-methyl acrylate-co-acrylic acid) and anisole show that domain growth rates increase with increasing quench depth and that crystallization immediately arrests domain growth and locks-in nonequilibrium structures. Light scattering measurements made on ternary solutions consisting of an amorphous poly(methyl methacrylate) dissolved in various ratios of 1-methyl-2 pyrrolidinone (solvent) and glycerin (nonsolvent) show that the domain growth rate exhibits a maximum at an intermediate quench temperature. Analysis of the results in terms of spinodal decomposition modeling shows that the maximum in the growth rate is related to an interplay between thermodynamic and transport effects that exists when solutions are quenched near the glass transition. In the third study, dark ground optical microscopy was used to study the effects of several additives on the rate of gelation and water influx during nonsolvent quenching of solutions based on a biodegradable polymer (poly(lactide-co-glycolide)) that are used in drug delivery applications. Comparison between the dark ground optical experiments and in-vitro drug release experiments show that additives that increase the rate of gelation increase the initial rate of drug release, or burst, while additives that slow the rate of gelation decrease the burst. These results suggest realistic ways of controlling the performance of certain types of drug delivery devices.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD