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

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.