Molecular diffusion and nuclear-magnetic-resonance relaxation of water in unsaturated porous silica glass

Measurements have been performed of the nuclear-magnetic-resonance longitudinal and transverse relaxation and the self-diffusion coefficient of deionized water confined in the porous space of a silica glass. The average pore diameter of the glass is 3.5 nm, and the experiments were conducted with different degrees of fluid filling. All three physical quantities were found to be linearly dependent on filling provided this was in excess of the amount of water corresponding to one monolayer, in agreement with theoretical predictions based on geometrical considerations. However, a deviation is observed below one monolayer, which is interpreted as a modification of the liquid-solid interface interaction, which causes the water molecules to become less mobile.