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 d(t)2 and inversely proportional to the tortuosity tau. 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 tau = D(b)/D, where D(b) is the bulk liquid self-diffusion coefficient, we derived values of tau in the range of 3.4-4.2. Using measured values of the permeability of organic liquids in Vycor and the value of tau, we determined d(t) = 31 angstrom. This value of d(t) is close to the pore radius obtained from desorption isotherms as well as to the value obtained from the Kozeny-Carman relation.