Generation of Nanovortices in Electroosmotic Flow in Nanochannels

Abstract

Electroosmotic flow in nanochannels is characterized by low Reynolds number in which flow mixing is difficult because of the dominant of molecular diffusion. Previous work shows that a heterogenerous surface potential can generate a vortical region within the bulk flow near the surface. But all of this work requires that the ionic species be pairs of ions of equal and opposite valence and the distribution of ions is not considered. In this work the electroosmotic flow in a rectangular nanochannel with non-uniform zeta potential is examined. This non-uniform wall potential creates a vortical structure having size proportional to the magnitude of the potential nonuniformity. The distributions of potential, velocity and mole fractions are calculated numerically. A circulation region within the bulk flow is observed near the non-uniform zeta potential which suggests mixing of the flow can be enhanced. The parameters that affect the circulation are investigated as well.