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, Henrik Bruus

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    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, Vrms1.5 V and f20 kHz, 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.
    Original languageEnglish
    JournalPhysical Review E
    Issue number5
    Pages (from-to)056305
    Publication statusPublished - 2007

    Bibliographical note

    Copyright 2007 American Physical Society


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