Viscous flow and diffusion of liquids in microporous glasses.

Abstract

The permeability for viscous flow of microporous materials is proportional to an effective pore cross-sectional area ${\mathit{d}}_{\mathit{t}}^{2}$ and inversely proportional to the tortuosity \ensuremath{\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 \ensuremath{\tau}=${\mathit{D}}_{\mathit{b}}$/D, where ${\mathit{D}}_{\mathit{b}}$ is the bulk liquid self-diffusion coefficient, we derived values of \ensuremath{\tau} in the range of 3.4--4.2. Using measured values of the permeability of organic liquids in Vycor and the value of \ensuremath{\tau}, we determined ${\mathit{d}}_{\mathit{t}}$=31 \AA{}. This value of ${\mathit{d}}_{\mathit{t}}$ is close to the pore radius obtained from desorption isotherms as well as to the value obtained from the Kozeny-Carman relation.