Gas flow through nanopores was simulated using a single-walled carbon nanotube model. Efficient protocols for the simulation of methane molecules in nanotubes were developed and validated for both self-diffusivity following a pulse perturbation, and for the transport diffusivity in an imposed concentration gradient. The former was found to be at least an order of magnitude lower than the latter, and to decline with increasing initial pressure, while the latter increased as the pressure gradient increased until it attained an asymptotic value. A previous analytical model, developed for single-file diffusion in narrow pores, was extended to treat wider pores for the case of single-species transport. The model, which predicted observed numerical results, assumed four regimes of transport. The dominant transport was ballistic motion near to the wall in not too wide nanotubes when a pressure gradient or concentration was imposed. This mode was absent in the case of self-diffusion due to periodic boundary conditions. Results were also presented for systematic comparisons of flexible versus rigid tubes and explicit atomic versus effective atomic potentials.

Single Species Transport and Self Diffusion in Wide Single-Walled Carbon Nanotubes. T.Mutat, J.Adler, M.Sheintuch: Journal of Chemical Physics, 2012, 136[23], 234902