Electrochemical Dynamics and Electrokinetic Particle Motion in Concentrated Electrolytes

Using the Poisson-Nernst-Planck (PNP) equations and modifications thereof, we consider two distinct systems under different conditions: an electrochemical and thermo-electric cell, and a colloidal particle in a concentrated electrolyte solution. For an electrochemical cell, we examine the response to a moderately nonlinear AC voltage and quantify the nonlinear impedance of the system, thus generalizing the concept of Electrochemical Impedance Spectroscopy beyond the low-voltage regime. With the same system, we study the response to a weak temperature gradient and quantify the charging dynamics of a model thermo-electric generator, yielding insights to the timescales over which such devices develop a thermo-voltage. We also study the electrophoresis (motion under an applied electric field) and diusiophoresis (motion under a solute concentration gradient) of a model colloidal particle in concentrated electrolytes. In the former case, we consider the effect that direct ion-ion electrostatic interactions has on particle mobility and achieve good agreement with experiments, including prediction of a reversal in the direction of particle migration. In the latter case, we examine the effect of steric repulsion between ions and predict a significant effect on the particle mobility. Our results suggest diusiophoresis could be a useful method for mobilizing particles in concentrated electrolytes.