The adsorption and diffusion mechanisms of argon at 120K were examined in a (25,0) single-walled carbon nanotube bundle using a combination of grand canonical Monte Carlo and microcanonical molecular dynamics simulations. Interstices between the single-walled carbon nanotubes provided the most energetically favorable adsorption sites and filled completely at low relative pressure, followed by adsorption in the single-walled carbon nanotubes. The self-diffusivities from the average mean squared displacements of argon molecules were calculated. In both flexible and rigid bundles, a bimodal diffusion mechanism was observed, with single-file diffusion occurring in the interstitial sites and Fickian diffusion in the single-walled carbon nanotubes. Strong system size effects were observed in these simulations. The largest system sizes showed very little influence of the nanotube flexibility on the diffusion of argon even at the lowest pressures studied.

Dual Diffusion Mechanism of Argon Confined in Single-Walled Carbon Nanotube Bundles. Liu, Y.C., Moore, J.D., Roussel, T.J., Gubbins, K.E.: Physical Chemistry Chemical Physics, 2010, 12[25], 6632-40