Induced charge electro-osmosis over controllably contaminated electrodes.

Recent studies in nonlinear electrokinetics reveal the standard theory to generally overpredict measured velocities, sometimes dramatically. Contamination of the driving surface provides a natural mechanism for electrokinetic suppression. We measure induced charge electro-osmosis over gold electrodes "contaminated" with silica layers of controlled thickness for nearly a thousand distinct conditions, in a system that enables direct comparisons between theoretical predictions and experimental measurements. Both the magnitude and frequency dependence of the measured slip velocity are captured quantitatively over the entire range of experiments by accounting for the physical capacitance and surface chemistry of the dielectric layer. More generally, the quantitative characterization enabled by our apparatus will prove invaluable for the rational design and prediction of electrokinetic systems.