Modeling the Effects of Mass Transfer on Microstructure Formation in Phase-Inversion Membranes

Self-assembled polymer membranes are typically produced by non-equilibrium processes, making the final microstructure a function of process history. When combined with complex thermodynamics, rheological complexity and a multitude of length and time scales, modeling the formation of these membranes is challenging. One promising path for model development combines continuum fluid dynamics with a field-theoretic description of polymer thermodynamics into a "multi-fluid" model. We have recently developed and validated such a model for a ternary polymer solution undergoing non-solvent induced phase separation. In a first step towards understanding polymer membrane formation, we examine the role of solvent and non-solvent exchange in driving phase inversion. The model predicts a wide variety of qualitative features of the phase inversion as a function of different parameters and initial conditions, including: immediate phase separation, delayed phase separation, single domain (dense) films and multiple domain (porous) films. We will discuss these different qualitative states and potential physical mechanisms of their origin.