Effect of solvent on diffusion: probing with nonpolar solutes.

Limiting mutual diffusion coefficients of carbon tetrachloride in methanol and of benzene, toluene, naphthalene, and biphenyl in cyclohexane as well as in ethanol at different temperatures are reported. These new data, together with literature diffusivities for the same probe solutes and for solute mesitylene in various solvents, are utilized to elucidate the effect of solvent on diffusion. Here, the data are consistent with our recent findings [J. Chem. Phys. 2013, 138, 224503] on the effects of free volume fraction, molar density, molecular mass, and fractional viscosity of solvent on diffusion. The results in this study show that the relation developed previously for solvent dependence of diffusion of disc-shaped solutes is also valid for spherical carbon tetrachloride. It is further found in this investigation that diffusivities are weakly dependent on a solvent's dielectric constant. A relation that includes the dielectric effect of solvent is demonstrated to be capable of describing the solvent dependence of diffusion of the nonpolar solutes of different shapes and sizes in this work to within an average deviation of ±2.7%. Comparisons with other diffusion models reveal that the newly developed relation is more accurate for representing the effect of solvent on diffusion. An expression for Zwanzig's "effective hydrodynamic radius" is also presented.