Numerical Simulation on the Formation of a Toroidal Microvortex by the Optoelectrokinetic Effect

Optoelectrokinetic effects were effectively used for rapid concentration of particles in microfluidics. In this study, we clarified detail mechanism of particle aggregation by numerical simulation using COMSOL v4.2a multiphysics software. A 3D simulation was conducted with axisymmetric boundary conditions. AC voltage was applied to the two parallel electrodes in a microchannel to generate temperature gradient in the fluids. In addition to the AC electrothermal (ACET) effect, local heating by a laser illumination was also considered. Numerical simulations were carried out for dielectric fluids. A toroidal microvortex induced by the optoelectrokinetic effect shows that fluid motions in the middle of bottom boundary are cancelled out by flows in opposite directions and consequently producing stagnation. It is expected that micro/nano particles can be deposited in the bottom electrode. Local heating by the laser illumination enhanced the intensity of microvortex substantially. It is confirmed that the dominant driving force for the microvortex is natural convection by the laser illumination, however AC voltage is necessary for particle aggregation in the spot area.