A Brief Introduction on the Electrokinetic Mixing and Separation in Microfluidic Systems

Abstract

Electrokinetics encompasses the analysis of fluid or particle motion in the electrical field; includes electroosmosis, electrophoresis, dielectrophoresis, electro-wetting, etc. Electrokinetic applications in the production of microfluidic systems have become quite attractive over the last decade. Electro-kinetic systems usually do not need any additional mechanical moving parts and may be made compact by removing the power source with a small battery. Electro-kinetic based microfluidic systems may also serve as a feasible method for developing a lab-on-a-chip (LOC) for use in biological and chemical assays. Here we discuss our work on electrokinetic based mixing and separation in microfluidic systems. First, we present a novel, fast, quasi-T-channel micromixer with electrically conductive sidewalls and some newly observed mixing process phenomena. The side walls of the microchannel may be parallel or non-parallel with an angle. In terms of velocity and scalar concentration distributions, the mixing activities in the micromixer with various angles between the two electrodes situated at the side walls are studied. It is observed that mixing can be quickly improved at a slight angle of about 5 ° between the two side walls of the electrode, also at low AC voltage, relative to parallel side walls. The efficacy of many parameters has been investigated for further development of the fluid mixing, including conductivity curve, AC electric flow frequency, applied voltage, AC signal phase change between the electrodes, etc. The findings demonstrate that the mixing is stronger under the high conductivity curve, low frequency , high voltage and 180^o signal phase change between the two electrodes. Quick mixing under high AC frequency can also be accomplished in this quasi-T-channel micromixer. The most significant discovery is that turbulence can be accomplished for the first time under the low Reynolds number AC electrokinetic force in the order of 1 in this novel configuration. As a consequence, turbulent mixing may also be produced in microfluidics to induce rapid mixing. The turbulent flow is often measured with a laser-induced photo bleaching anemometer.