271348 Role of Electro-Osmosis in Microchannel-Nanochannel Impedance Response

Tuesday, October 30, 2012: 12:30 PM
Fayette (Westin )
Jarrod Schiffbauer, Mechanical Engineering, Technion--Israeli Institute of Technology, Haifa, Israel and Gilad Yossifon, Mechanical Engineering, Technion, Technion City, Israel

Electrical Impedance Spectroscopy (EIS) has been used extensively for the experimental study and characterization of ion-exchange membranes. The impedance characteristics and the appearance of a tangent line at an apparently universal 45 degree angle for the region near the cut-off of the so-called Warburg branch of the impedance plane (Nyquist) plot are predicted and understood in terms of equivalent circuit models and have been derived from fundamental electro-diffusion.  However, despite the myriad of current applications, a similarly comprehensive study of microchannel-nanochannel interfacial impedance response has not been undertaken. Here we present some fundamentally new experimental results showing similar Warburg response to membrane systems at zero bias and a deviation from the constant-angle Warburg response seen in membrane systems, resulting in a decrease in the tangent angle increasing with applied current in microchannel-nanochannel devices.  Curious features in the Bode plots distinct from those of membrane systems are also shown. The experimental results are analyzed in terms of a fundamental theory relating some of these differences in response to the presence and AC perturbations of electro-osmotic flow in the microchannel-nanochannel system, resulting in modification of the standard Warburg-type impedance term as well as streaming contributions to the impedance.

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