2018 Volume 26 Pages 114-119
The drift motion of a particle under an external electric field, which is termed electrophoresis, is originated from the coupling between the responses of the particle and the ions in the electric double layer surrounding the particle. Since the response of the ions varies as the level of the external field, physics of nonlinear response in the electrophoresis has not been understood. We investigate the nonlinear electrophoretic response of a particle in a salt-free medium. Hydrodynamic equations for the dynamics of ionic distribution and solvent flow are directly solved by the smoothed profile method in order to clarify the response of the electric double layer to the external field. The electrophoretic mobility turns out to first increase and then saturate with an increase of the strength of the external field. These two different nonlinear electrophoretic responses are found to originate from the gradual counterion stripping and the change in electroosmotic flow due to the asymmetrized ionic distribution of the electric double layer.