Interplay of Induced Charge Electroosmosis and Electrothermal Flow in Insulator-Based Dielectrophoresis
Physical Review Fluids
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Insulator-based dielectrophoresis (iDEP) is an emerging technique for particle manipulation in microfluidic devices. Two nonlinear electrokinetic flows have been demonstrated to take place simultaneously in iDEP: one is induced charge electroosmosis (ICEO) due to the electric polarization of the insulator, and the other is electrothermal flow (ETF) due to the amplified Joule heating of the fluid around the insulator. These flows vary differently with the applied electric field, and become strong in a fluid with a low and a high electric conductivity, respectively. They both exhibit the pattern of fluid vortices near the insulator but with opposite circulating directions. We present in this work an experimental study of the interplay of ICEO and ETF in a constricted microchannel under dc-biased ac voltages. We also develop a depth-averaged numerical model to simulate the coupled electrokinetic fluid flow with the charge and energy transport. The experimentally measured nonlinear fluid velocity agrees closely with the numerical prediction for both a wide range of buffer concentrations and a range of ac voltages. It also matches asymptotically the predicted velocity of ICEO in a low-concentration buffer under a small ac voltage and that of ETF in a high-concentration buffer, both of which are consistent with a scaling analysis. Interestingly, the nonlinear fluid velocity becomes marginal in moderate-concentration buffers under moderate ac voltages because of the opposing effects of ICEO and ETF.
Electro-osmosis; Microfluidic devices
Electrical and Computer Engineering
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Interplay of Induced Charge Electroosmosis and Electrothermal Flow in Insulator-Based Dielectrophoresis.
Physical Review Fluids, 6(9),