Diffusion in viscous solvents. Part 4.—Viscosity and interdiffusion coefficients for solutions of carbon tetrabromide and of naphthalene in di-isobutyl phthalate and their dependence on temperature

Abstract

Interdiffusion coefficients of carbon tetrabromide and of naphthalene dissolved in di-isobutyl phthalate have been obtained by following the isothermal relaxation of a concentration gradient induced by the application of a temperature gradient in the vertical direction in a thin horizontal film of the solution. Limiting diffusion coefficients at infinite dilution have been obtained over a range of temperatures and combined with some new data on the viscosity of the solvent to obtain ‘Stokes–Einstein numbers’. These are much lower than those expected on the basis of the Stokes–Einstein–Sutherland continuum model, being even lower than those found in diol solvents. However, the value found for naphthalene at 298 K in this ester solvent agrees closely with that derived from independent determinations of the diffusion coefficient of naphthalene in a hydrocarbon solvent having the same viscosity as di-isobutyl phthalate.