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Published on: February 1, 2017
Selection of nonequilibrium overlimiting currents: universal depletion layer formation dynamics and vortex
Gilad Yossifon1, Hsueh-Chia Chang
1Department of Chemical and Biomolecular Engineering, Center for Microfluidics and Medical Diagnostics, University of Notre Dame, Notre Dame, Indiana 46556, USA.
Physical Review Letters
|December 31, 2008
Summary
Researchers imaged ion flux in a nanoslot to study overlimiting current density. They observed a vortex instability that controls ion flow, independent of external stirring.
Area of Science:
- Electrokinetics
- Nanofluidics
- Membrane Science
Background:
- Overlimiting current density in nanoporous membranes is a nonequilibrium phenomenon.
- Understanding ion flux dynamics is crucial for membrane performance.
- Previous theoretical work predicted vortex instabilities in such systems.
Purpose of the Study:
- To image ion flux dynamics across a straight nanoslot.
- To investigate the nonequilibrium phenomenon of overlimiting current density.
- To understand the role of electrokinetic instabilities in controlling ion transport.
Main Methods:
- Direct imaging of ion flux across a nanoslot.
- Application of a slow alternating current (AC) field.
- Observation of ion-depletion front formation and evolution.
Main Results:
- An ion-depletion front was intermittently generated from the nanochannel end.
- A predicted vortex instability was observed to arrest self-similar diffusive front growth.
- The electrokinetic instability evolved into a stationary interfacial vortex array.
- This vortex array determined the overlimiting current, irrespective of external flow.
Conclusions:
- Vortex instabilities play a critical role in regulating overlimiting current density in nanoporous membranes.
- The observed interfacial vortex array provides a mechanism for stable, high ion flux.
- These findings offer insights into controlling ion transport in nanofluidic devices.
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