Simulation of block-copolymer-membrane fabrication*

SNIPS - a sequence of evaporation-induced self-assembly (EISA) and subsequent, nonsolvent-induced phase separation (NIPS) of block copolymer solutions - provides a bottom-up approach to fabricate integral-asymmetric, isoporous block copolymer membranes. Initially, EISA creates a self-assembled, well-ordered, functional top layer of perpendicular cylindrical domains. Subsequently, as the film contacts the nonsolvent bath, NIPS fabricates a macroporous mechanical support. To optimize permeability, selectivity, longevity, and cost, and to rationally design fabrication processes, direct insights into the spatiotemporal structure evolution are necessary.

Using a single, highly coarse-grained, particle-based model in conjunction with large-scale multi-GPU simulations, we study both processes, EISA and NIPS, focusing on the complex interplay between evaporation and solvent-nonsolvent exchange, micro- and macrophase separation, and kinetic arrest as the plasticizing solvent leaves the dense, polymer-rich domains. The simulations identify a process window that allows for the successful fabrication of integral-asymmetric, isoporous diblock copolymer membranes, and contribute to understanding the interplay of the different structural and thermodynamic (e.g., solvent selectivity for the block copolymer components) as well as kinetic (e.g., plasticizing effect of the solvent) characteristics.