Current-induced ion concentration polarization at a perfect ion-exchange patch in an infinite insulating wall

Abstract

This research examines, theoretically, the ion concentration polarization, ion fluxes, and electrostatic fields near an ion- exchange patch in the wall of an electrified fluidic channel. These phenomena are important in related microfluidic ion- preconcentration systems. Under an electric field, counter ions enter the ion-exchange patch at one side and leave at the other, with salt depletion occurring near the entrance and accumulation near the exit. The high patch conductivity and the concentration profiles lead to local electric field perturba- tions that may facilitate preconcentration. This study includes analytical expressions of ion concentrations and electrochemical potentials at small to moderate electric fields, as well as numerical simulations. Additionally, a simple matrix of poly- nomial coefficients (obtained via fitting of numerical data) enables analytical calculation of the two-dimensional concen- tration profiles at all electric fields within the range investigated in the numerical simulations. This is possible because a single dimensionless parameter controls this problem.