(505e) Effect of Intedigitated Electrode Asymmetry on Performance of Carbon Based AC Electroosmotic Micropumps

The increased research interest in Alternating Current Electroosmotic (ACEO) micropumps over the past few decades is due to the many advantages ACEO pumps present compared to other approaches. These advantages include the low power consumption and the absence of movable mechanical parts, which reduces complexity and manufacturing cost. Although a few studies have been previously reported on the effects of electrode geometry on the performance of ACEO micropumps, it is still unclear how the asymmetry ratio of interdigitated electrodes affects the pumping rate of these devices. The present research investigates the effect of the asymmetry of interdigitated electrodes on the performance of carbon-based ACEO micropumps. The conventional carbon-based microelectromechanical systems (C-MEMS) technique which employs photolithographic patterning of a photoresist precursor, followed by pyrolysis to form glassy carbon structures, is utilized to fabricate interdigitated carbon microelectrode arrays.

To explore the effect of asymmetry of interdigitated microelectrodes on the overall fluid velocity, planar carbon electrode arrays with electrode width ratios of 60/20 μm, 80/20 μm, and 100/20 μm, with separation between electrode pairs of 20 μm were fabricated. Bi-distilled water (Ï? = 1.72 μS/cm) was used as a working fluid to measure the pumping rate of carbon ACEO micropumps. An AC voltage ranging from 2 to 20 V_pp at frequencies from 1 to 200 kHz was applied to induce ACEO flow in a polydimethylsiloxane microchannel 100 microns high and 500 microns wide. For all the cases, as the AC frequency decreased, the fluid velocity increased in the applied frequency range. At low amplitudes (less than 8 V_pp), the fluid velocity increased as the voltage increased. The fluid velocity was decreasing at mid-range amplitudes (10-14 V_pp), and the flow direction was reversed at high amplitudes (16 - 20 V_pp). The flow reversal at high amplitudes might be attributed to the dominant ACEO vortex reaching the top of the microchannel, eliminating the conveyor-belt effect thus propelling the fluid to the opposite direction. As the asymmetry of interdigitated electrodes decreased, the fluid velocity increased for both forward and backward flows. The maximum observed fluid velocities were 28.6 μm/s, 11.44 μm/s and 7.3 μm/s in the forward direction, and 338 μm/s, 106.56 μm/s and 79.65 μm/s in the backward direction, for the interdigitated carbon microelectrodes with ratios of 60/20, 80/20, and 100/20 μm, respectively. Interestingly, the flow rate increased as the ratio of asymmetry decreased for the tested ratios. The likely explanation for this trend is that as the width of the wider electrode decreases, portion of the dominant flow over this electrode increases, thus more fluid volume is driven by this vortex. We expect that findings of this study will be useful for the design of high performance ACEO micropumps based on asymmetric interdigitated electrode arrays.