Diffusion mechanism of CO₂ in a crystalline polymer membrane studied using model gases

Abstract

Molecular dynamics simulation was performed for a crystalline form of syndiotactic polystyrene, the form, which may be used as a separation and storage material by using the nanoscale cavities in the crystal. The diffusion process of penetrants in the crystal was simulated using model gases, in which the bond length, , and Lennard-Jones parameters, and , were systematically varied, based on CO₂ and N₂. The diffusion coefficients increased with and decreased with increasing and . The behaviour was interpreted in terms of the change in crystal cell dimensions induced by the adsorption of gas molecules. The diffusion behaviour in the form is very sensitive to the lattice parameters, which are also very sensitive to gas adsorption. The results are useful for molecular design of gas separation membranes in which the gas permeability is controllable by external stimulus.

Keywords::

• molecular dynamics simulation
• polymer
• crystal
• diffusion
• carbon dioxide

Acknowledgements

This work was partly supported by MEXT/JSPS KAKENHI, Grant-in-Aid for Scientific Research (C), 19550121. The numerical calculations were carried out on System A/B at the Institute for Information Management and Communication, Kyoto University. The usage costs of these systems were contributed by the Center for Information Initiative, University of Fukui.