Test of Hubbard-Onsager's dielectric friction theory for ion migration in mixed solvents. I. Ethanol-water systems

Abstract

In order to test the Hubbard-Onsager (HO) dielectric friction theory for ion mobility in mixtures of polar solvents, the theory has been generalized within the same framework to a system which has two dielectric relaxation times by using the superimposed Debye polarization fields related to the two kinds of dipoles. The same form of linear differential equation for the determination of the velocity field is reached only with the modified definition of the HO radius. The numerical solutions to the differential equation are fitted to a polynomial to facilitate a systematic application of the HO theory. The HO theory is reasonably well successful in predicting the dependence of the residual friction coefficient Δζ (=ζ-4πηR) on ion size and solvent composition for the alkali metal and halide ions even if no effects of the ions on solvent properties are taken into account. It turns out that the HO theory is by far better than the Zwanzig theory. Limitations of the HO theory combined with bulk properties of solvent are exhibited for the relatively large ions, in particular, below the solvent composition where the solvent has a maximum viscosity. © 1986 American Institute of Physics.