Dual control volume grand canonical molecular dynamics was used to study the diffusivity of a mixture of nitrogen and oxygen in a graphite slit pore as a function of pore width. The evidence supported combined viscous and diffusive transport through the narrow slit pores. The viscous contribution to the flow became weaker as the pore width decreased. The fluid velocity profiles showed evidence of microscopic slip but still retained a classical Navier-Stokes parabolic signature. The concentration profiles for each component in the mixture exhibited an approximately linear variation with distance along the pore length; suggesting that cross-coupling effects were weak. It was found that the diffusion of oxygen-nitrogen mixtures through a graphite pore exhibited a complex dependence upon the pore width. Molecular packing appeared to play a significant role in determining the flow of the mixture. Thermodynamic effects were of more importance than were sieving effects and thus no greater diffusivity was found for oxygen than for nitrogen.

Transport Diffusion of Oxygen-Nitrogen Mixtures in Graphite Pores: a Non-Equilibrium Molecular Dynamics (NEMD) Study. Travis, K.P., Gubbins, K.E.: Langmuir, 1999, 15[18], 6050-9