MOBILITY OF THE 2 D ADSORBED PHASESSTUDY OF THE MOBILITY OF AN HYPERCRITICAL TWO-DIMENSIONAL FLUID BY QUASI-ELASTIC NEUTRON SCATTERING

Abstract

The adsorption of methane on a compressed form of exfoliated graphite (papyex) is characterized from a thermodynamical point of view by measuring a few adsorption isotherms. It is shown that the sample offers homogeneous (0001) surfaces and is well suited for neutron scattering studies. From the broadening of the incoherent neutron quasi-elastic peak, we are able to determine the diffusion coefficient of the two-dimensional hypercritical fluid of methane adsorbed on the graphite basal plane. We also measure its variation as a function of the coverage. The change in the diffusion coefficient is important, from 13 to 2.2 x 10-5 cm2 s-1 in the 0.45-0.9 coverage range and for T= 90 K, and consistent with a hole mobility model