Methane dynamics in porous xerogels characterized by small-angle and quasielastic neutron scattering

The melting behavior of methane adsorbed in a porous silica xerogel has been examined by quasielastic neutron scattering (QENS) from 20 to 115 K. The methane dynamics indicate a heterogeneous xerogel surface with a distribution of rotational and translational diffusion barrier heights from 0.17 to 2.1 kJ/mole. The QENS elastic intensity structure factor indicates that rotational diffusion occurs about a C2 molecular axis for methane adsorbed in the xerogel. Porous silica and aluminosilica xerogels have also been characterized by small-angle neutron scattering (SANS) and gas adsorption isotherm measurements to determine the porosity, pore size, and tortuosity of the pore network.