Nonlinear Phenomena in Induced Charge Electroosmosis

Abstract

We present an experimental and numerical investigation of induced charge electroosmosis (ICEO) on a planar electrode surface directly in contact with a high conductivity electrolytic solution. Symmetric rolls of ICEO flow were produced on the electrode by placing it in an AC electric field. The slip velocity was measured for a range of AC voltages and frequencies using micro particle image velocimetry (μPIV). The slip velocity was also calculated by finite element simulations based on a linear and a nonlinear model of electrical double layer, respectively. The μPIV measurements were found to be much lower (two and half orders of magnitude) than the velocities predicted by the linear model. The linear model is valid only under Debye Huckel approximation (φ ≪ kBT/e = 25 mVolt at room temperature) which does not hold true for practical situations. The nonlinear model, on the other hand, predicts velocities which are lower than the linear model and closer to the experimental values. The nonlinearity reduces discrepancy between experimental and numerical results by approximately an order of magnitude. The nonlinear model accounts for nonlinear capacitance of the double layer and lateral conduction of charge in the double layer.