Molecular simulations of organic solvent transport in dense polymer membranes: Solution-diffusion or pore-flow mechanism?

Abstract

We employed non-equilibrium molecular dynamics simulations and theoretical predictions to elucidate organic solvent and water transport mechanisms in dense polymer membranes. Our study investigated the transport of water and 14 organic solvents across 16 dense polymer membranes with varying fractional free volumes. Simulations demonstrated that the dependence of organic solvent or water flux on applied pressure exhibited minimal deviation from linearity, contrary to the prediction of a “ceiling flux” at high pressures, based on the solution-diffusion model. Notably, our findings underscore the paramount influence of solvent size and membrane pore size on solvent permeance, significantly diverging from the solvent solubility-based predictions of the solution-diffusion model. Overall, our results agree with the solution-friction model for characterizing water and organic solvent transport in dense polymer membranes such as reverse osmosis and organic solvent nanofiltration. These fundamental insights into the transport mechanisms of water and organic solvents offer molecular-level guidance for designing next-generation high-performance polymer membranes for various separation applications.