Space-charge-perturbed electrophoresis in nonpolar colloidal dispersions

This paper reports the observation of bipolar, space-charge-perturbed transport in colloidal dispersions using an experimental technique that time-resolves electrophoresis in nonpolar colloidal systems. Unlike existing methods for studying electrophoresis, this technique can be applied to dispersions of diverse types and concentrations over a wide range of electric fields, including the space-charge-perturbed conditions often encountered in practical applications. The phenomenon is investigated as a special case of dielectric relaxation in a leaky capacitor connected in series to a perfect one. Using the first principle charge transport theory, such dielectric relaxation, occurring under the non-Ohmic supply and space-charge-perturbed transport conditions, is shown to differ from that expected by the conventional equivalent-circuit treatment. The combined theoretical analysis and the experimental technique provides a means for independently determining the densities and mobilities of charged species in such systems. Using a liquid developer for electrography as a prototype system, results are presented that illustrate the power of the technique as a new tool to provide new insights into the generic transport and generation mechanisms of charged species in colloidal systems. (C) 1996 American Institute of Physics.