129Xe NMR as a probe of the dynamics of gas confined in porous Vycor

We use 129Xe NMR to probe the diffusion of xenon gas in the porous network of Vycor glass, by monitoring its relaxation properties. When the mean free path of the diffusing gas is larger than the pore size (Knudsen conditions), both 129Xe chemical shifts and relaxation rates are sensitive to the confinement of xenon gas within a porous solid. The influence of both temperature and xenon pressure are recorded on the 129Xe chemical shifts and relaxation rates, in order to characterise the xenon/Vycor interactions. Monte Carlo (MC) and Molecular Dynamics (MD) simulations, using a numerical model of Vycor, are required to interpret the relaxation properties of xenon. MD simulations clearly establish the occurrence of confined diffusion of xenon within Vycor, related to the geometry of this porous media. This work shows the potentiality of NMR relaxation to obtain dynamical information on the diffusion within porous media.