MOLECULAR MODELING SIMULATION OF GAS-TRANSPORT IN AMORPHOUS POLYIMIDEAND POLY(AMIDE IMIDE) MEMBRANE MATERIALS

Molecular dynamics (MD) simulations were used to investigate the trans port of different gases in a poly(amide imide) (PAI) and two polyimide s (PI1 and PI2). The agreement between measured and simulated average diffusion coefficients (D) was acceptable. There was, however, a consi derable scattering of the D values for the individual simulated gas mo lecules. While MD simulations are still not an ideal tool for the quan titative prediction of gas permeation properties of polymers, these me thods can be used to obtain a better insight about the gas transport m echanism. Transport of small molecules occurs by jumps between individ ual sections of the free volume (holes) through temporarily open chann els. The main difference between the PAI and the two polyimides is bro ader and slightly more permanent channels in the case of the PAI. Solu bility investigations using the Widom method revealed a predominantly Henry sorption mechanism for hydrogen, a dual-mode sorption with a hig h degree of Langmuir-type immobilization for oxygen and nitrogen. Copy right (C) 1996 Elsevier Science Ltd.