Electrokinetic behavior of colloidal particles with thin ionic double layers

The phenomenological equations that govern the nonequilibrium behavior of the ionic diffuse double layer surrounding an isolated, charged coloidal particle are considered. An approximate solution is constructed that is valid when the ratio of the Debye length to the characteristic particle dimension is small. This solution is applicable to a particle that is subjected to an external perturbation composed of an arbitrary linear combination of steady, axisymmetric electrical, hydrodynamical, or concentration gradient fields. Hence, this analysis provides a unified approach to the treatment of the entire class of admissible problems in the thin double layer approximation. Specific applications are shown to the problems of electrophoresis and dilute shear viscosity of a suspension of uniform, noninteracting spherical colloidal particles. Comparison with the numerical results of previous investigators shows that the solutions are accurate over much of the parameter range of practical interest in colloidal suspensions. The role of the zeta potential and the mobilities, valences, and concentrations of the dissolved ions on electrokinetic phenomena are examined.