Phase-field modeling of non-solvent induced phase separation (NIPS) for PES/NMP/Water with comparison to experiments

We develop a phase-field model to simulate the formation of porous polymeric membranes via non-solvent induced phase separation. The material system of interest is PES/NMP/Water (Polyethersulfone/N-methyl-2-pyrrolidone/Water), however the approach is broadly applicable to other materials. The three-component system is represented with two field variables: one representing the volume fraction of polymer, and the other the fractional composition of non-solvent N (water) vs solvent S (NMP). The exchange of solvent and non-solvent is solved with a Fickian diffusion model, thus capturing the in-flux of the coagulation bath into the polymer solution. As a demonstration of the predictive capabilities of the model, the concentration of solvent (NMP) in the coagulation bath was varied to draw comparisons with experiments. Two- and three-dimensional simulations were carried out to evaluate the cross-sectional pore morphology and the top surface pore size for membranes formed by NIPS. Experiments involving handcast membranes of a similar system were performed for comparison with the simulations, and an agreement was found concerning the dependence of pore morphology on the composition of the coagulation bath.