Nonlinear electrophoresis of colloidal particles

Advances over the past decade in nonlinear electrophoresis of charged, dielectric colloidal particles in aqueous electrolytes are reviewed. Here, the word nonlinear refers to the fact that the ratio of the electrophoretic speed of the particle to the magnitude of the applied electric field—the electrophoretic mobility—is not independent of field strength. This is in stark contrast to the vast majority of work on (linear) colloidal electrophoresis over the last century, where the mobility is assumed to be a material property dependent only on the particle–electrolyte combination. The present discussion is focused on: (i) experimental measurements of the field-dependent mobility; (ii) an asymptotic scheme to calculate the mobility in the common thin-Debye-layer limit; and (iii) computations of nonlinear electrophoresis from numerical solution of the electrokinetic equations. The article concludes with suggestions for future work in this evolving area of colloid science.