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Following a general symmetry argument, I suggest using locally asymmetric electric geometries to pump liquid in channels or drive droplets on surfaces. This strategy, which requires no global gradient in the pumping direction, should be of interest for microfluidic devices and micro-electro-mechanical systems. A practical realization consists in using polar periodic arrays of electrodes addressed by an ac voltage difference. A simple electro-osmotic model provides an estimate of the pumping velocities achievable.
Armand Ajdari (Sat,) studied this question.