Concentration polarization around polyelectrolyte-coated electrodes. Model and observations

Abstract

An investigation on the phenomenon of concentration polarization (CP) in conducting porous particles is presented in this work, considering both bare and polyelectrolyte-coated particles. The conducting nature of the porous structure brings about the induction of a surface (and hence volume) charge distribution by the applied external field. The polymer charge (with its counterions from solution) is superimposed on this field-induced component. From the solution of Poisson’s equation, the concentration and potential profiles are evaluated, and from them, the concentration polarization can be calculated. The results are presented as concentration perturbation as a function of time after application of the field, both for bare and coated particles. Experiments are also performed aimed at measuring the CP using a solution of fluorescent dye (rhodamine B). From the increase or decrease of fluorescence, the concentration perturbations are observed around the particle. Importantly, depletion of concentration is observed on both sides of the particle when this is bare. In contrast, if the particles are coated, the classical pattern of a pole of increased concentration and an opposite one of decreased concentration is found. Dielectric dispersion experiments in suspensions of bare and brush-coated particles confirm this fact.