In order to make clear the relationship between the pore structure and the diffusivity, permeation simulations of pure gases through simple model membranes were carried out by using the external-field non-equilibrium molecular dynamics method. The membrane was modelled as slit-shaped pores having periodic belt-like heterogeneous pore surfaces caused by the upheaval of surface atoms. By applying simulation results for membranes with several upheaval interval distances to Maxwell-Stefan theory, the effects were calculated, of the molecular loading of permeating molecules in the pores, upon Maxwell-Stefan diffusivity (DMS). The permeation potential barrier was estimated to be the difference between the maximum and minimum permeation potential energies. The effects of molecular loading upon the permeation potential barrier and DMS were in inverse proportion. It was noted that, when the width of the adsorption area in the permeation direction was not a common multiple of the molecular diameter, the permeation potential barrier decreased with increasing molecular loading. This was because the positive force against the permeation direction was caused by interactions with permeating molecules in the adsorption area between adjacent upheavals. It was therefore suggested that the key factor in controlling diffusion was the structural relationship between the adsorption area and the permeating molecules.

Non-Equilibrium Molecular Dynamics Simulation Study on Permeation Phenomena of LJ Particles in Slit-Shaped Membranes with Periodic Belt-Like Heterogeneous Surfaces. Yonemori, K.I., Takitani, A., Furukawa, S.I., Nitta, T., Takahashi, H., Nakano, M.: Fluid Phase Equilibria, 2007, 257[2], 190-4