Methane mobility in carbon nanotubes

Quasi-elastic neutron scattering has been used to characterize the diffusiv ity of CH, molecules condensed in single-wall carbon nanotubes. It is shown that the two sites of adsorption, previously observed by adsorption volume try 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 th e more weakly bound site at 70 < T < 120 K. The diffusion coefficients of t he mobile molecules range between 3 x 10(-7) to 15 x 10(-7) cm(2) s(-1). Th e fraction of this viscous liquid diminishes as the temperature is decrease d; the adsorbate is fully solidified at 50 K and below. (C) 2000 Elsevier S cience B.V. All rights reserved.