(29a) Design of Pore Wall Chemistry to Control Solute Transport and Selectivity

Developing next-generation membranes for water purification demands system-specific materials with precisely tuned functionality. Advances in synthesis have led to the fabrication of isoporous membrane materials with functionalizable pore walls. However, a fundamental understanding of how the chemistry of the wall affects the transport of water and solutes remains elusive, and current practices for avoiding pernicious issues such as fouling largely rely on existing heuristics and trial-and-error methods. Simulations enable the nanoscopic investigation of the mechanism by which pore wall chemistry controls its hydration water and thus its water-mediated interactions with solute molecules. Here, we use molecular dynamics simulations to investigate water and solute structure, dynamics, and transport in a cylindrical nanopore patterned with nonpolar methyl and polar hydroxyl groups. We find that the pore wall chemistry induces structural changes in water near the wall, which lead to differences in macroscopic transport metrics that persist even when the pore is large enough for water in the center of the pore to demonstrate bulk-like behavior. These surface effects furthermore have a significant impact on solute transport through the pore, suggesting that it is possible to achieve solute selectivity via wall functionalization. We thus apply an optimization procedure based on a genetic algorithm to design the chemical patterning of the pore wall to maximize selectivity for a given solute. This inverse design procedure and the accompanying molecular-level understanding of the effect of chemical heterogeneity on solute selectivity in a pore will inform the design of more efficient water purification membranes, as well as the modulation of water-mediated surface-molecule interactions in other systems.