Molecular dynamics simulations of rigid defect-free single-walled carbon 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 material. These simulations overestimated the molecular diffusion coefficients because they neglected energy exchange between the diffusing molecules and the nanotube. Other careful simulations of molecular self-diffusion had allowed for nanotube flexibility. The same method was used here to examine the influence of nanotube flexibility upon the diffusion of CH4 in (20,0) and (15,0) nanotubes. The inclusion of nanotube flexibility reduced the transport diffusion, relative to the rigid nanotube, by roughly an order of magnitude when close to zero pressure. At pressures above about 1bar, the diffusivities for flexible and rigid nanotubes were very similar; differing by less than a factor of two on average. Hence, the diffusivities were still extremely large as 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