Self-diffusion of a molecule in porous Vycor glass

We have measured the self-diffusion coefficient (DS) of a dye molecule (azobenzene) in solution in porous Vycor glass by the technique of forced Rayleigh scattering. We find that the value of DS for motion in the pore space is about 2 orders of magnitude less than for free diffusion in bulk solution. By derivatizing the active surface sites we have separated the roles of the chemical and physical features of the pore space on diffusion. We believe this to be the first measurement of self-diffusion in solution in porous Vycor which has been proposed to have a fractal pore structure.