Viscous flow and diffusion of liquids in microporous glasses

The permeability for viscous flow of microporous materials is proportional to an effective pore cross-sectional area dₜ² and inversely proportional to the tortuosity {τ}. The tortuosity of microporous Vycor glass was determined from measurements of the self-diffusion coefficients D of hexane and decane using small angle neutron scattering. From the relation for the tortuosity {τ}=Db/D, where Db is the bulk liquid self-diffusion coefficient, we derived values of {τ} in the range of 3.4--4.2. Using measured values of the permeability of organic liquids in Vycor and the value of {τ}, we determined dₜ=31 {}. This value of dₜ is close to the pore radius obtained from desorption isotherms as well as to the value obtained from the Kozeny-Carman relation.