The technique of 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. Evidence was found in support of combined viscous and diffusive transport through these narrow slit pores. The viscous contribution to the flow became weaker as the pore width decreases. The fluid velocity profiles showed evidence of microscopic slip but still retain a classical Navier-Stokes parabolic signature. The concentration profiles for each component in the mixture showed 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 displays a complex dependence upon the pore width. Molecular packing appeared to play a very significant role in determining the flow of the mixture. Thermodynamic effects were of more importance in these simulations than sieving effects; hence, no greater diffusivity was found for oxygen as compared with nitrogen.

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