Abstract
Direct evidence is provided for the transition from surface conduction (SC) to electro-osmotic flow (EOF) above a critical channel depth () of a nanofluidic device. The dependence of the overlimiting conductance (OLC) on is consistent with theoretical predictions, scaling as for SC and for EOF with a minimum around . The propagation of transient deionization shocks is also visualized, revealing complex patterns of EOF vortices and unstable convection with increasing . This unified picture of surface-driven OLC can guide further advances in electrokinetic theory, as well as engineering applications of ion concentration polarization in microfluidics and porous media.
- Received 16 July 2013
DOI:https://doi.org/10.1103/PhysRevLett.114.114501
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