Field-effect control of electro-osmotic flow with synchronized AC-switching of channel and gate potentials

Electroosmotic flow (EOF) in a microchannel can be controlled electronically by use of an electrode embedded in the wall of the channel. By setting a voltage to the electrode, the zeta-potential at the wall can be changed locally. Thus, the electrode acts as a "gate" for liquid flow, in analogy with a gate in a field-effect transistor. This paper describes the control of EOF by the synchronized switching of the gate potential with the channel axial potential. The advantage of this procedure is that potential gas formation by electrolysis at the electrodes that provide the axial electric field is suppressed, while the direction and magnitude of the EOF can be maintained. The results show that the flow velocity is linearly dependent on the applied gate potential and varies with the phase difference between the applied gate and channel potential. An analysis of the time constants involved in the charging of the insulator, and therewith the switching of the zeta potential, is made in order to predict the maximum operating frequency.