Dynamics of Membrane Structure Formation in Quenched Polymer Solutions

152 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1998.The Cahn-Hilliard approach is extended to the study of phase separation in ternary polymer/solvent/nonsolvent systems. Three systems are studied: PMMA/N-methyl-2-pyrrolidinone [NMP]/glycerol, for which experimental data are available, and two common membrane-forming systems, poly(ether sulfone) [PES]/dimethylsulfoxide [DMSO]/water and cellulose acetate [CA]/acetone/water. The effects of quench temperature and initial solution composition on the predicted structure-formation dynamics are elucidated. For the PMMA/NMP/glycerol system, model predictions agree well with real-time data obtained from light scattering measurements. Predicted pore growth rate curves exhibit a relative maximum with both quench temperature and nonsolvent composition. For shallow quenches (higher quench temperatures and lower nonsolvent content) near a phase boundary, the pore growth rate increases with increasing quench depth while for deep quenches, where the composition of the polymer rich phase approaches that of a glass, the pore growth rate decreases with increasing quench depth. This behavior seems to be a universal phenomenon in quenched polymer solutions which can undergo a glass transition, and is result of an interplay between thermodynamic and kinetic driving forces for phase separation.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD