Interaction of gas molecules with crystalline polymer separation membranes: Atomic-scale modeling and first-principles calculations

Carbon dioxide (CO2)-induced plasticization can significantly decrease the gas separation performance of membranes in high-temperature or high pressure conditions, such as industrial methane (CH4) separations. In this paper, we investigated the crystalline phase of three polymers (polybenzimidazole (PBI), bis(isobutylcarboxy)polybenzimidazole (PBI-Butyl), and Kapton™) and interactions between gas molecules (CO2 and N2) and these polymers. A novel, molecular dynamics (MD) based, computational technique was employed to find unknown crystalline structures of these polymer materials. The interaction of CO2 and N2 gases with these crystals was studied by first-principles calculations and by classical MD simulations. The results provide useful information for qualitative understanding the permeability, diffusivity, and plastic swelling in these materials caused by gas molecules absorbed in a polymer matrix.