Gas flow through nanopores was simulated by using a single-walled carbon nanotube model. Efficient protocols for the simulation of methane molecules in nanotubes were developed and validated for both the 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 reached an asymptotic value. A previous analytical model, developed for single-file diffusion in narrow pores, was extended to wider pores for the case of single species transport. The model, which predicted the observed numerical results invokes four regimes of transport. The dominant transport was by ballistic motion near 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 from systematic comparisons of flexible versus rigid tubes and explicit atom versus effective atomic potentials were also presented.

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