Electroosmotic flow reversal outside glass nanopores

Nadanai Laohakunakorn, Vivek V. Thacker, Murugappan Muthukumar, Ulrich F. Keyser

Research output: Contribution to journalArticlepeer-review


We report observations of a striking reversal in the direction of electroosmotic flow (EOF) outside a conical glass nanopore as a function of salt concentration. At high ionic strengths (>100 mM), we observe EOF in the expected direction as predicted by classical electrokinetic theory, while at low salt concentrations (<1 mM) the direction of the flow is reversed. The critical crossover salt concentration depends on the pore diameter. Finite-element simulations indicate a competition between the EOF generated from the inner and outer walls of the pore, which drives flows in opposite directions. We have developed a simple analytical model which reveals that, as the salt concentration is reduced, the flow rates inside the pore are geometrically constrained, whereas there is no such limit for flows outside the pore. This model captures all of the essential physics of the system and explains the observed data, highlighting the key role the external environment plays in determining the overall electroosmotic behavior.

Original languageEnglish
Pages (from-to)695-702
Number of pages8
JournalNano Letters
Issue number1
Publication statusPublished - 14 Jan 2015


  • Electroosmosis
  • fluid dynamics
  • microfluidics
  • nanopores

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