A Multi-Fluid Model of Phase-Inversion Membrane Formation

Industrial processes for producing polymer-based materials operate away from equilibrium, making the final microstructure – and thus the properties of the material – dependent on process history. Describing such processes by traditional simulation methods has proven difficult because of the confluence of complex thermodynamics and non-trivial fluid mechanics. We have recently developed a “multi-fluid” simulation framework for examining the dynamics of multiphase polymer solutions that combines a field-theoretic approach to thermodynamics with continuum fluid mechanics. In this framework, we use a ternary polymer solution model to investigate the phase inversion process for making polymer membranes. After characterizing the model and methods, we investigate a number of important phenomena that occur across several length and time scales including (i) mass-transfer between the polymer film and the non-solvent bath, (ii) phase separation between polymer lean and polymer rich regions and (iii) long-time coarsening behavior. We will further discuss the implications of these results on the formation mechanisms of various microstructures found in polymer membranes.