Experiments on AC electrokinetic pumping of liquids using arrays of microelectrodes

Net fluid flow induced by ac potentials applied to arrays of co-planar interdigitated microelectrodes is reported. Two types of microelectrode structures have been employed: arrays of unequal width electrodes subjected to a single ac signal, and arrays of identical electrodes subjected to a traveling-wave potential. A square glass chamber was constructed around the electrode arrays and filled with a concentration of KCl in water of conductivity around 1 mS/m. A map of the fluid velocity as a function of voltage (0-8 Vpp) and frequency (0.1-100 kHz) is presented for the traveling-wave array. 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 flow regimes. The observations at low voltages are in qualitative accordance with an ac electroosmotic model based upon the Debye-Huckel theory for the double layer.