(682e) Sorption-Relaxation Behavior in Polymers of Intrinsic Microporisity during Gas Separation from Molecular Simulations

Polymers of intrinsic microporosity (PIMs) are high free volume polymers that can function as molecular sieves, making PIMs alternative materials for separation applications. These polymers are unable to pack efficiently due to their rigidity and contorted shapes, which results in their desirable porosity. Our group has been investigating the permeability and selectivity of gases in PIMs using atomistic molecular simulations. In this work, we further improve our predictive capability by considering the motion of the polymer framework during adsorption (sorption-relaxation scheme) by repetitively implementing a hybrid simulation of molecular dynamics and Monte Carlo simulation (MD/MC). A python package, pysimm, was used to facilitate the workflow between MD and MC simulators (LAMMPS and Cassandra). Structural properties, such as radial distribution function, were compared in the presence and the absence of the sorption-relaxation scheme. The permeability and selectivity of important gas pairs such as CO₂/CH₄ and O₂/N₂ were evaluated at typical industrial gas conditions including the presence of H₂S and water. Our results suggested that hybrid MD/MC simulations can provide important insights for future adsorption studies. This procedure can be applied to other polymeric membranes, composite membranes, and flexible porous materials to account for possible swelling, relaxation, gate-opening, or breathing phenomena within the frameworks.