It was recalled that molecular dynamics simulations of rigid defect-free single-walled C nanotubes had previously suggested that the transport diffusivity of gases adsorbed in these materials could be orders of magnitude higher than in any other nanoporous materials. These simulations over-estimated the molecular diffusion coefficients because they neglected energy exchange between the diffusing molecules and the nanotube. However, careful simulations of molecular self-diffusion had been reported which allowed for nanotube flexibility. An efficient thermostat was used to examine the influence of nanotube flexibility upon the transport diffusion of CH4 in (20,0) and (15,0) nanotubes. The inclusion of nanotube flexibility reduced the transport diffusion relative to that of a rigid nanotube by about an order of magnitude close to zero pressure. At pressures above about 1bar, the transport diffusivities for flexible and rigid nanotubes were very similar; usually differing by less than a factor or two. The transport diffusivities were still extremely large when compared with other known materials, when flexibility was taken into account.

Transport Diffusion of Gases is Rapid in Flexible Carbon Nanotubes. H.Chen, J.K.Johnson, D.S.Sholl: Journal of Physical Chemistry B, 2006, 110[5], 1971-5