On the interpretation of electrokinetic potentials

The variation of the dielectric constant and the viscosity in the electrical double layer are considered. The Helmholtz-Smoluchowski equation for the electrophoretic mobility requires only insignificant correction for variations in the dielectric constant; the variation in the viscosity can lead to considerable corrections, which increase with surface potential and concentration. Equations are given for the relation between electrophoretic mobility and surface potential and are illustrated by two examples. The concept of the slipping plane should be replaced by a slipping layer of finite thickness. At high surface potentials, the electrophoretic mobility is independent of the potential but depends on the electrolyte concentration.