AC electrokinetic pumping of liquids using arrays of microelectrodes

Abstract

The precise control and manipulation of small masses of liquids is an important requirement in the lab-on-a-chip technology. Net fluid flows induced by ac potentials applied to arrays of co-planar interdigitated microelectrodes are reported. Two types of microelectrode structures have been studied: arrays of unequal width electrodes subjected to a single ac signal, and arrays of identical electrodes subjected to a travelling-wave potential. Experiments were performed using solutions of KCl in water of conductivities around 1mS/m placed on top of the electrodes. Fluorescent latex particles were used as tracers. In both microstructures, two fluid flow regimes have been observed: at small voltage amplitudes the fluid moves in a certain direction, and at higher voltage amplitudes the fluid flow is reversed. The fluid flow seems to be driven at the level of the electrodes in the two regimes. A theoretical model of ac electroosmosis is described. The model is based upon the Gouy-Chapman-Stern theory of the double layer. The theoretical results are in qualitative accordance with the experimental observations at low voltages.