Combined viscoelectric and steric effects on the electroosmotic flow in a microchannel under induced high zeta potentials

Abstract

Although the concepts of steric and the viscoelectric effects in the analysis of electrokinetic flows have been studied previously in nanochannels (Hsu et al., 2016), in the present work, their influence is extended to microchannels. The governing equations of Bikerman's Modified Poisson–Boltzmann (MPB) equation and the momentum conservation equation are solved numerically for an electroosmotic flow of a Newtonian fluid in a microchannel. Here, the excluded volume of the crowding of ions via steric factor is considered when high ionic concentration and large effective ionic size of the buffer solution are taken into account; also, the viscoelectric effect is present when high zeta potentials are induced and controlled by shielding electrodes at the walls of the microchannel. The results show a significant competition of the studied effects within the thin electric double layer, modifying the predictions from the classical velocity profiles of electroosmotic flows where the mentioned effects are not considered. It is reported that increasing the magnitude of the zeta potentials does not necessarily increase the volumetric flow rate as determined from the classical Poisson–Boltzmann (PB) theory. To validate the numerical solution, an approximate analytical solution for the velocity field for slightly high zeta potentials was determined.