Coarsening Kinetics of Ternary Polymer Solutions with Mobility and Viscosity Contrasts

Nonsolvent induced phase separation (NIPS) is a technique to make polymer membranes. In NIPS, a polymer solution film is immersed in a nonsolvent bath, inducing phase separation and eventual solidification of the film into a membrane. Though NIPS has been in use for decades, the formation of important membrane features, such as asymmetric pore size distribution, still remains a mystery. To understand how these features are formed, we built a phase-field simulation software capable of solving coupled diffusion and momentum equations that describe the NIPS system. Our stable pseudo-spectral methods allow us to simulate systems at the micron length-scale for millisecond time-scales. In this talk, we report how coarsening—a major factor in shaping bulk membrane morphology—behaves when mobility and viscosity contrasts are present among the NIPS components. We consider both diffusion-only coarsening and coarsening with hydrodynamics. We also look at the effect of dimensionality, comparing coarsening in 2D and 3D.