Methane mobility in carbon nanotubes

Quasi-elastic neutron scattering has been used to characterize the diffusivity of CH, 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 x 10(-7) to 15 x 10(-7) cm(2) s(-1). The fraction of this viscous liquid diminishes as the temperature is decreased; the adsorbate is fully solidified at 50 K and below. (C) 2000 Elsevier Science B.V. All rights reserved.