Relationship between diffusion, self-diffusion and viscosity

We investigate the experimental limits of validity of the Stokes–Einstein equation. There is an important difference between diffusion and self-diffusion. The experimental evidences show, that in the case of self-diffusion the product Dη/T is constant and the Stokes–Einstein equation is still valid. On the other hand, comparison of existing experimental data, on viscosity η and diffusion coefficients D, of small, fast moving ions shows unambiguously that the product Dη/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 for fast moving ions.