Nonlinear electrokinetics at large voltages
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Bazant_Nonlinear electrokinetics.pdf
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1.17 MB
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Author(s)
Bazant, Martin Z.
Kilic, Mustafa Sabri
Storey, Brian D.
Ajdari, Armand
Date Issued
July 2009
Journal
New Journal of Physics
Publisher
IOP Publishing
Citation
Martin Z Bazant et al. "Nonlinear electrokinetics at large voltages ." 2009 New J. Phys. 11 075016 © 2009 IOP Publishing
Version
Final published version
Abstract
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.
MIT Department
Massachusetts Institute of Technology. Department of Chemical Engineering
Massachusetts Institute of Technology. Department of Mathematics
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DOI of Published Version
https://doi.org/10.1088/1367-2630/11/7/075016
