Nanoscale electrokinetics and microvortices: How microhydrodynamics affects nanofluidic ion flux

Hsueh Chia Chang, Gilad Yossifon, Evgeny A. Demekhin

Research output: Contribution to journalArticlepeer-review


When a direct current (DC) electric field is applied across an ion-selective nanoporous membrane or a nanochannel with an overlapping Debye layer, a surprising microvortex instability occurs on the side of the membrane/channel through which counterions enter. Despite its micro and nano length scales, this instability exhibits all the hallmarks of other classical hydrodynamic instabilitiesa subharmonic cascade, a wide-band fluctuation spectrum, and a coherent structure dominated by spatiotemporal dynamics. Moreover, the resulting convection enhances the ion flux into the ion-selective medium and gives rise to an overlimiting-current bifurcation in the current-voltage relationship. This hydrodynamically driven nonequilibrium ion flux does not seem to have any equivalent in cell membrane ion channels. Yet, by introducing asymmetric entrances to provide different polarized regions and/or viscous arrest of the vortex instability, one can fabricate a hydrodynamic nanofluidic diode. With other modifications, hysteretic, excitable, and oscillatory ion flux dynamics could also be elicitedall with strong hydrodynamic features.

Original languageEnglish
Pages (from-to)401-426
Number of pages26
JournalAnnual Review of Fluid Mechanics
StatePublished - 2011
Externally publishedYes


  • Depletion front
  • Extended polarization
  • Nanoslot ion current
  • Overlimiting current
  • Rectification


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