Microstructure Evolution during Nonsolvent-Induced Phase Separation: A Joint Experimental–Computational Investigation into Membrane Formation

Our current fundamental understanding of morphology evolution during nonsolvent-induced phase separation (NIPS) is limited to insights developed from qualitative observation and trial-and-error experimentation. Emerging particle and field-based simulation methods offer a powerful framework for quantitatively describing the NIPS process and understanding the formation of specific microstructures (e.g., nodules, micropores, or macrovoids). However, such simulations are seldom validated against experimental analyses at similar conditions. In this study, experimental polysulfone (PSf)-based ternary NIPS membrane-forming systems, referenced in this work as casting solutions or dopes, are analyzed alongside phase-field simulated membrane structures. Experimental and simulation results consistently demonstrated strong relationships between Flory–Huggins χ parameters and thermodynamics, kinetics, and membrane morphology arising from the NIPS process. Notably, in both analyses, increasing values of the χns parameter describing binary interactions between nonsolvent (n) and solvent (s) components improved overall casting solution thermodynamic stability while increasing shrinkage and micropore content of resulting PSf membranes. Increasing the χnp parameter between the nonsolvent and PSf (p) accelerated NIPS demixing kinetics. Manipulation of individual χ parameters in phase-field simulations provided further insight on the influence of pairwise thermodynamic interactions on membrane formation. Although some features like nodules or macrovoids cannot presently be generated in phase-field simulated membrane structures, the overall agreement between experimental and computational efforts in this study represents an important step forward in the development of physically accurate NIPS modeling techniques.