Enhanced mixing performance of electrokinetic flows in a cross-junction microchannel with sawtooth structures

In this paper, we propose a micromixer with the combination of a flow-focusing region and sawtooth structures, to study the mixing performance of electrokinetic (EK) flow under the impact of an alternating current (AC) electric field by means of numerical simulations. The Helmholtz-Smoluchowski theory is applied to approximate the electric double layer (EDL) effect. Focusing on the effects of sawtooth structures and AC electric field frequencies on mixing efficiency of electrokinetic micromixers, the concentration distributions and velocity distributions within micromixers have been studied. The numerical simulation results demonstrate that this micromixer has an excellent mixing performance for Newtonian solutions. Additionally, a proper sawtooth structure is conducive to enhancing the mixing efficiency of an electrokinetic micromixer, which is due to the generation of vortices at the junction edges. The presence of vortices leads to the enhancement of fluid disturbance and the enlarged contact area between fluids, contributing to a more complete mixing for electrokinetic flows. Moreover, it is found that as the AC electric frequency is reduced, the mixing efficiency is enhanced for such novel electrokinetic micromixer. The low electric frequency causes the velocity of electro-osmotic flow to decrease, promoting the molecular diffusion as the primary mixing mechanism, which improves the mixing efficiency. This work provides important insights for the application of sawtooth structure on electrokinetic micromixers, and serves as a crucial reference for the integration of active and passive techniques in microfluidic technology.