A Simple New Method for Determining Diffusion Coefficients of Interacting Particles in Porous Silica and Gels

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Abstract
A new experimental method to measure the diffusion coefficients of interacting particles in porous silica is described. The diffusion behavior of NaNO3 from a porous silica sphere into a solution of NaCl was found to be very sensitive to the cross diffusion term when the concentration ratio of NaCl to NaNO3 was high. The diffusion behavior of NaCl, KNO3, and KI from the inside to the outside of the sphere was also examined. Theoretical equations to analyze the cross diffusion flows of interacting particles were derived. The cross diffusion coefficient of NaNO3 and NaCl as well as the diffusion coefficients NaNO3, NaCl, KNO3, and KI in porous silica were evaluated from the present experimental results. The obtained diffusion coefficients were found to be about one third of those in solution. The diffusion behavior of NaNO3, NaCl, KNO3, and KI from spherical polyacrylamide gel was also examined for comparison.