Block copolymer membrane fabrication via EISA and NIPS

The SNIPS process -- combining evaporation-induced self-assembly (EISA) with nonsolvent-induced phase separation (NIPS) -- offers a versatile bottom-up route for fabricating integral-asymmetric, isoporous block copolymer membranes. During EISA, solvent evaporation drives the self-assembly of a highly ordered top layer composed of perpendicularly aligned cylindrical domains, providing selectivity for ultrafiltration and water purification. Subsequent immersion in a nonsolvent bath triggers NIPS, generating a porous, mechanically robust substructure from the same material. During solvent exchange, reduced polymer mobility induces glassy arrest within the copolymer domains, preserving the emerging nonequilibrium morphology.

Despite its success, rational design of SNIPS membranes remains challenging. The final morphology represents a nonequilibrium structure governed by a complex interplay of coupled processes: solvent evaporation, self-assembly, solvent–nonsolvent exchange, macrophase separation, and glassy arrest -- spanning broad structural, thermodynamic, and kinetic parameter ranges.

To optimize membrane permeability and selectivity and to establish predictive design principles, we investigate the full SNIPS process by concurrently combining large-scale particle simulations with continuum modeling based on the Uneyama-Doi model. The relevant spatiotemporal domain studied by the computationally intense particle simulations is efficiently identified by machine learning. The simulation scheme identifies the key parameters defining the process window for successful membrane formation and reveal mechanistic insights into how molecular and processing factors govern morphology. These results provide a unified framework for the rational design of SNIPS-based membrane fabrication and offer valuable guidance for experimental optimization.