Nonlinear electrokinetics at large voltages

Details Nonlinear electrokinetics at large voltages Nonlinear electrokinetics at large voltages

Jul 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009njph...11g5016b&link_type=abstract

New Journal of Physics, Volume 11, Issue 7, pp. 075016 (2009).

Physics

8

Scientific paper

The classical theory of electrokinetic phenomena assumes a dilute solution of point-like ions in chemical equilibrium with a surface whose double-layer voltage is of order the thermal voltage, kBT/e=25 mV. In nonlinear 'induced-charge' electrokinetic phenomena, such as ac electro-osmosis, several volts ≈100kBT/e are applied to the double layer, and the theory breaks down and cannot explain many observed features. We argue that, under such a large voltage, counterions 'condense' near the surface, even for dilute bulk solutions. Based on simple models, we predict that the double-layer capacitance decreases and the electro-osmotic mobility saturates at large voltages, due to steric repulsion and increased viscosity of the condensed layer, respectively. The former suffices to explain observed high-frequency flow reversal in ac electro-osmosis; the latter leads to a salt concentration dependence of induced-charge flows comparable to experiments, although a complete theory is still lacking.

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