Study Of Micromixers Based On AC Electrokinetics

Chip-scale micromixing is an important branch of microfluidic research.However,mixing in microfluidic chips is limited by small size of microchannels(usually at micro level),as well as the low Reynolds number laminar flow.Since molecular diffusion is the primary mechanism for mixing in laminar flow,it would take a long time to accomplish the mixing process.AC electrokinetic approach have attracted particular recognition due to many advantages,such as simple structure,low cost,low voltage,easy to be integrated and no electrolysis.This paper presents two novel micromixers which utilize AC electroosmosis(ACEO)and AC electrothermal(ACET)effect to promote mixing of fluids in microchannel.These two micromixers are studied by numerical simulation and experiment in this work.At first,this paper summarized the research status of microfluidic chip and micromixer all over the world.The mechanism of electric double layer and ACEO flow as well as the velocity model of ACEO flow based on equivalent circuit method are introduced,besides,the mechanism and model of ACET effect is introduced as theoretical basis for design of micromixers.Then we proposed an ACEO micromixer with asymmetric electrodes based on the characteristics of ACEO flow.The mathematical and physical model of this micromixer is established.The 3D numerical simulations of two solutions' mixing is performed by solving the Navier-Stokes and convection-diffusion equations in microchannel.The flow field and concentration field is studied to explain the working principle of the micromixer.Influences of several key parameters on mixing efficiency are discussed in our simulation,such as width ratio of electrodes,the gap of electrodes,the length of electrodes and the offset distance of electrodes pair.Furthermore,effects of applied voltage and frequency,Reynolds number,conductivity of fluid on mixing efficiency are also investigated.In this work,another novel micromixer which utilizes thermally biased ACET effect to promote mixing is proposed based on the characteristics of ACET flow and the mathematical and physical model is established.And multiphysics(electrical,temperature,fluid flow and concentration fields)in this mixer is numerically studied to illuminate how the mixer works.Effects of heater's geometric parameters,heat flux of heater,flow rate and conductivity of fluid on mixing efficiency are also studied.Besides,a solution to the problem that high temperature appears when mixed high conductivity fluid is put forward.At last,the experimental study of these two micromixers is carried out.The micromixers which consist of gold electrodes patterned on to glass wafer substrate and PDMS microchannel aligned onto substrate are fabricated for experiment.And dilution experiment was performed for these mixers by using dye solution as verifications for our designs and numerical simulation.The research results provide a theoretical and experimental basis for the rapid mixing of microfluidics.