Molecular modelling simulation of gas transport in amorphous polyimide and poly(amide imide) membrane materials

Molecular dynamics (MD) simulations were used to investigate the transport of different gases in a poly(amide imide) (PAI) and two polyimides (PI1 and PI2). The agreement between measured and simulated average diffusion coefficients (D) was acceptable. There was, however, a considerable scattering of the D values for the individual simulated gas molecules. While MD simulations are still not an ideal tool for the quantitative prediction of gas permeation properties of polymers, these methods can be used to obtain a better insight about the gas transport mechanism. Transport of small molecules occurs by jumps between individual sections of the free volume (holes) through temporarily open channels. The main difference between the PAI and the two polyimides is broader and slightly more permanent channels in the case of the PAI. Solubility investigations using the Widom method revealed a predominantly Henry sorption mechanism for hydrogen, a dual-mode sorption with a high degree of Langmuir-type immobilization for oxygen and nitrogen. Copyright (C) 1996 Elsevier Science Ltd.