Gas permeance in polymer membranes: computational approaches near and far from ideal behavior*

The use of highly specialized membranes for gas separations processes presents a valuable opportunity for a global shift away from traditional thermally driven, carbon-intensive methods. The vast design space for polymers makes it desirable to explore new materials in silico before synthesizing them to conserve valuable resources. Using a combination of molecular dynamics and Monte Carlo methods, we explore gas permeance behaviors of several materials including ladder polymers, polyimides, and polysulfones using fully atomistic simulations. From the solution-diffusion method we use Grand Canonical Monte Carlo to deduce the solubility of gas molecules both near and away from the dilute Henry’s Law limit and use molecular dynamics to evaluate gas diffusion coefficients as a function of gas loading. The use of non-equilibrium molecular dynamics is also explored. Finally, we note how the use of detailed simulations with atomistic force fields combined with an iterative feedback loop provides an opportunity for the accelerated development of soft materials in important engineering applications.