Suppression of electro-osmotic flow by surface roughness.

We show that nanoscale surface roughness, which commonly occurs on microfabricated metal electrodes, can significantly suppress electro-osmotic flows when excess surface conductivity is appreciable. We demonstrate the physical mechanism for electro-osmotic flow suppression due to surface curvature, compute the effects of varying surface conductivity and roughness amplitudes on the slip velocities of a model system, and identify scalings for flow suppression in different regimes of surface conduction. We suggest that roughness may be one factor that contributes to large discrepancies observed between classical electrokinetic theory and modern microfluidic experiments.