Diffusion coefficients of selected solvents (acetone, acetonitrile, chloroform, cyclohexane, toluene, water) in porous sol-gel glass were measured using the radioactive tracer diffusion method and the diaphragm technique.The concentrations of the solvents were determined using IR and scintillation measurements. Selected samples had their internal surface modified by replacing hydroxyl groups with trimethylsilane groups. It was shown that molecular translational motion inside the pores is hindered by pure geometrical restrictions and surface interactions. It was found that polar molecules diffuse faster than inert molecules. Experimental results were explained in terms of the model developed by Korb et al. Results obtained for cyclohexane were compared with molecular dynamics computer simulations, and the tortuosity factor was evaluated. The diffusion coefficient for acetone within the pores was studied over the temperature range 284-315 K, and the activation energy was determined.
Diffusion coefficients of water and cyclohexane in porous sol-gel glass of
average pore diameter 2.9 nm were obtained using a radioactive tracer
technique. This information was applied to calibrate the membrane in the
diaphragm cell which was subsequently used to measure the diffusion
coefficients for cyclohexane, acetone, toluene, acetonitrile, and
chloroform. Results for cyclohexane were compared with computer simulation
of molecular motion of cyclohexane in a model cylindrical pore of diameter
2.9 nm. Translational motion of polar liquids inside the pores was found to
be faster than that of neutral, not wetting solvents.
Abstract. Diffusion coefficients for water, cyclohexane, toluene, chloroform, acetone and acetonitrile in porous sol-gel glass were determined using the diaphragm and radioactive tracer techniques. Polar solvents were .found to diffuse faster than nonpolar solvent within porous sol-gel glass. The diffusion coefficients of Nd 3+ and Er a+ inside porous sol-gel glass were determined from concentration profiles within monoliths impregnated by 1.6M rare earth salts dissolved in either acetone or water. To study the effects of ligands on the diffusion, four different erbium salts were used: nitrate, chloride, bromide, and perchloride. It was found that the diffusion rate increases with decreasing radius of rare earth coordination sphere.
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