FLUID TRANSPORT IN PARTIALLY FILLED POROUS SOL-GEL SILICA GLASS

Measurements of low-frequency ac electrical conductivity of a porous glass filled with different amounts of a saline solution are compared with the self-diffusion coefficient of water measured in the same sample, reported previously [F. DOrazio et al., Phys. Rev. Lett. 63, 43 (1989)]. The two transport parameters are consistently related through the Einstein relation under saturation conditions. A more complex picture is revealed for the unsaturated sample, since the presence of a vapor phase enhances the self-diffusion coefficient. Conductivity experiments allow an independent assessment of the contribution to self-diffusion from the liquid phase. However, a comparison between the two experiments indicates that the role of the vapor phase is not well understood. © 1990 The American Physical Society.