A simulation tool was presented in order to predict gas permeation through heterogeneous microphase separated structures. The method combined dissipative particle dynamics with kinetic Monte Carlo. Morphologies obtained from dissipative particle dynamics were mapped onto a high density grid on which gas diffusion takes place. Required input parameters for the kinetic Monte Carlo calculations were the gas solubility and gas diffusion constant within each of the pure phase components. The method was tested and validated for permeation of H2, O2 and N2 gases through hydrated Nafion membranes at various temperatures and water contents. It was predicted that membranes which contained an equal volume fraction of water, those with the highest ion exchange capacity exhibited the largest N2 and O2 permeation rates. For membranes of the same ion exchange capacity the H2, O2 and N2 and permeability increased approximately linearly with Bragg spacing. It was also predicted that O2 gas permeation depended much more upon bottleneck phenomena within the phase separated morphologies than H2 gas permeation. Overall, the calculated H2 and O2 permeability was found to be slightly lower than experimental values. This was attributed to the robustness of dissipative particle dynamics resulting in ∼7 larger Bragg spacing as compared with experiment and/or increased gas solubility within the polymer phase with water uptake.

Modeling Gas Permeation through Membranes by Kinetic Monte Carlo: Applications to H2, O2, and N2 in Hydrated Nafion. G.Dorenbos, K.Morohoshi: Journal of Chemical Physics, 2011, 134[4], 044133