Diffusion in a Fractal System

The surface geometry of Vycor porous glass was examined by using the relative permeability (PR) technique in a H2O/He system. At a water relative pressure of approximately 0.3, a maximum is observed on the PR curve. This maximum is explained in terms of geometrical changes taking place due to the deposition of a water film on the internal Vycor surface. When the sample is dry, diffusion in a fractal system is found to be more appropriate in describing the process. When the sample is wet, the diffusion process obeys classical Knudsen theory for smooth cylinders. Copyright 1998 Academic Press.