Flow reversal at low voltage and low frequency in a microfabricated ac electrokinetic pump

Misha Marie Gregersen, Laurits Højgaard Olesen, Anders Brask, Mikkel Fougt Hansen, and Henrik Bruus
Phys. Rev. E 76, 056305 – Published 9 November 2007

Abstract

Microfluidic chips have been fabricated in Pyrex glass to study electrokinetic pumping generated by a low-voltage ac bias applied to an in-channel asymmetric metallic electrode array. A measurement procedure has been established and followed carefully resulting in a high degree of reproducibility of the measurements over several days. A large coverage fraction of the electrode array in the microfluidic channels has led to an increased sensitivity allowing for pumping measurements at low bias voltages. Depending on the ionic concentration a hitherto unobserved reversal of the pumping direction has been measured in a regime, where both the applied voltage and the frequency are low, Vrms<1.5V and f<20kHz, compared to previously investigated parameter ranges. The impedance spectrum has been thoroughly measured and analyzed in terms of an equivalent circuit diagram to rule out trivial circuit explanations of our findings. Our observations agree qualitatively, but not quantitatively, with theoretical electrokinetic models published in the literature.

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  • Received 30 March 2007

DOI:https://doi.org/10.1103/PhysRevE.76.056305

©2007 American Physical Society

Authors & Affiliations

Misha Marie Gregersen, Laurits Højgaard Olesen, Anders Brask, Mikkel Fougt Hansen, and Henrik Bruus

  • MIC–Department of Micro and Nanotechnology, Technical University of Denmark, DTU Building 345 East, DK-2800 Kongens Lyngby, Denmark

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Issue

Vol. 76, Iss. 5 — November 2007

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