Transient characteristics of electric double layer charging and the associated induced-charge electrokinetic flow

Abstract

This paper presents a detailed numerical analysis of the transient characteristics of electric double layer (EDL) charging and the associated induced-charge electrokinetic (ICEK) flow around an ideally polarizable cylinder. To this end, we solved numerically the coupled Poisson-Nernst-Planck and Navier-Stokes equations with the finite element method. The numerical simulation provides an unprecedented full-field (including the EDL region) characterization of the transient evolutions of ion transport, electric potential, and fluid flow during the EDL charging. The simulation results show that the EDL charging is driven by the electric current normal to the cylinder surface. With EDL being charged, the charge density in the EDL counteracts the local external electric field on the cylinder surface to reduce the electric current, which then leads to the slowing down of the EDL charging. At the steady state, the EDL becomes fully charged and the charge density in EDL exactly counteracts the external electric field, and then the EDL charging stops. During the EDL charging, the interaction of the external electric field with the charge density in the EDL drives the liquid in the EDL to move first, and then as time evolves, the liquid in the bulk electrolyte sets in motion because of the momentum transfer between the EDL and the bulk. These findings are conducive to the understanding of the transient dynamics of ICEK phenomena around polarizable objects.