Relaxation Effects in the Electrophoresis of Disperse Systems

Abstract

IT was shown by Henry¹ that the movement of spherical particles in an electric field depends on the size of the particle and the ionic strength and that the relationship between mobility and zeta-potential depends on the radius of the particle, a, and the Debye-Hüickel double layer thickness, 1/ϰ. It was pointed out by Overbeek² that, in addition, the relaxation of the ionic atmosphere of the particle must be considered. Overbeek² and Booth³ treated this problem theoretically and obtained analytical expressions for the mobility, which included corrections for retardation and relaxation, in terms of an incomplete power series in zeta-potential the coefficients of which were functions of ϰa. The limitation of the equations of Overbeek and Booth was that the expressions were only valid for zeta-potentials less than 25 mV. More recently Wiersema⁴ has obtained a numerical solution of the problem which gives mobility as a complete power series in zeta-potential and is valid for potentials greater than 25 mV.