Transport diffusion of oxygen-nitrogen mixtures in graphite pores: A nonequilibrium molecular dynamics (NEMD) study

The technique of dual control volume grand canonical molecular dynamics (DC V GCMD) is used to study the diffusivity of a mixture of nitrogen and oxyge n in a graphite slit pore as a function of pore width. We find evidence in support of combined viscous and diffusive transport through these narrow sl it pores. The viscous contribution to the flow becomes weaker as the pore w idth decreases. The fluid velocity profiles show evidence of microscopic sl ip but still retain a classical Navier-Stokes parabolic signature. The conc entration profiles for each component in the mixture show an approximately linear variation with distance along the pore length, suggesting that cross -coupling effects are weak. We find that the diffusion of oxygen -nitrogen mixtures through a graphite pore displays a complex dependence upon the par e width. Molecular packing appears to(-) play a very significant role in de termining the flow of the mixture. Thermodynamic effects are of more import ance in these simulations than sieving effects; hence, we do not find a gre ater diffusivity for oxygen compared to nitrogen.