Combined diffusive and viscous transport of methane in a carbon slit pore

The transport of mass through porous materials can occur by essentially two different mechanisms: (1) diffusion and (2) viscous flow. The former occur s when there is a gradient in chemical potential of the pore fluid, while t he latter occurs in the presence of a pressure gradient. In general, fluid transport occurs by both of these mechanisms and their respective contribut ions to the total intra-pore Bur are approximately additive. Experimentally , there is no unambiguous way of determining the individual contributions t o the total flux of these two modes of transport. Fortunately, molecular si mulations does provide a solution. We present a novel simulation method in which the separate contributions to the total flux are determined. The method involves the use of two non-equi librium molecular dynamics techniques: dual control volume grand canonical molecular dynamics (DCV GCMD) and an algorithm for simulating planar Poiseu ille flow. We apply this technique to study the combined (viscous and diffu sive) transport of methane through single slit-shaped graphite pores of wid th 2.5, 5.0 and 10.0 methane diameters. We End that the viscous contributio n to the total intrapore flux through each of these pores is 10%, 15% and 3 4%, respectively.