Molecular Simulation of Gas Transport Through Cylindrical Pores

Recent developments in self-assembled block copolymers make it possible to synthesize regular porous nanofiltration membranes, which could potentially push the separation limit of gas mixtures. While experimental and theoretical efforts have been made to investigate this problem, a quantitative understanding is still missing. We perform molecular dynamics simulation of binary hard spheres diffusing through rigid membranes filled with cylindrical pores. Particle diffusivity is found to be proportional to pore size, following the Knudsen diffusion mechanism. A power-law trade-off relationship between permeability and selectivity is obtained, which is consistent with the Freeman theory of gas separation via disordered polymeric membranes. The dependence of the upper bound limit on the size ratio of gas particles is extracted. The effect of polydispersity on membrane pore size is examined.