Methane mobility in carbon nanotubes

Quasi-elastic neutron scattering has been used to characterize the diffusivity of CH4 molecules condensed in single-wall carbon nanotubes. It is shown that the two sites of adsorption, previously observed by adsorption volumetry and calorimetry measurements, correspond to a solid-like phase for the more strongly bound site at T<120 K and to a liquid-like component for the more weakly bound site at 70<T<120 K. The diffusion coefficients of the mobile molecules range between 3×10−7 to 15×10−7 cm2 s−1. The fraction of this viscous liquid diminishes as the temperature is decreased; the adsorbate is fully solidified at 50 K and below.