Relationship between Diffusion, Selfdiffusion and Viscosity

TL;DR

This paper examines the limits of the Stokes-Einstein equation's validity, highlighting differences between diffusion and self-diffusion, and showing that the equation does not hold for small, fast ions where D/T varies with temperature.

Contribution

It clarifies the conditions under which the Stokes-Einstein equation is valid, especially distinguishing between diffusion and self-diffusion in experimental data.

Findings

Self-diffusion D/T remains constant with temperature.

Diffusion of small ions shows D/T depends on temperature.

Stokes-Einstein equation fails for fast-moving ions.

Abstract

We investigate the experimental limits of validity of the Stokes-Einstein equation. There is an important difference between diffusion and self-diffusion. There are experimental evidences, that in the case of self-diffusion the product D /T is constant and the equation is still valid. However, comparison of existing experimental data on viscosity and diffusion coefficients D of small, fast moving ions unambiguously show that the product D /T depends strongly on temperature T. The temperature dependence of diffusion coefficient declines from that of viscosity. Therefore, the Stokes-Einstein equation is not valid in this case.