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# Induced-charge electro-osmosis

Squires, Todd M. and Bazant, Martin Z. (2004) Induced-charge electro-osmosis. Journal of Fluid Mechanics, 509 . pp. 217-252. ISSN 0022-1120. http://resolver.caltech.edu/CaltechAUTHORS:SQUjfm04

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## Abstract

We describe the general phenomenon of ‘induced-charge electro-osmosis’ (ICEO) – the nonlinear electro-osmotic slip that occurs when an applied field acts on the ionic charge it induces around a polarizable surface. Motivated by a simple physical picture, we calculate ICEO flows around conducting cylinders in steady (DC), oscillatory (AC), and suddenly applied electric fields. This picture, and these systems, represent perhaps the clearest example of nonlinear electrokinetic phenomena. We complement and verify this physically motivated approach using a matched asymptotic expansion to the electrokinetic equations in the thin-double-layer and low-potential limits. ICEO slip velocities vary as $u_s \,{\propto}\,E_0^2 L$, where $E_0$ is the field strength and $L$ is a geometric length scale, and are set up on a time scale $\tau_c \,{=}\,\lambda_D L/D$, where $\lambda_D$ is the screening length and $D$ is the ionic diffusion constant. We propose and analyse ICEO microfluidic pumps and mixers that operate without moving parts under low applied potentials. Similar flows around metallic colloids with fixed total charge have been described in the Russian literature (largely unnoticed in the West). ICEO flows around conductors with fixed potential, on the other hand, have no colloidal analogue and offer further possibilities for microfluidic applications.

Item Type: Article "Reprinted with the permission of Cambridge University Press." Received May 5 2003; Revised February 13 2004; Published Online 07 Jun 2004 The authors would like to thank E´cole Supe´rieure de Physique et Chimie Industrielles (Laboratoire de Physico-chimie Th´eorique) for hospitality and partial support, and the referees for extensive comments and Russian references. This research was supported in part by the US Army through the Institute for Soldier Nanotechnologies, under Contract DAAD-19-02-0002 with the US Army Research Office (M. Z.B.), and by the NSF Mathematical Sciences Postdoctoral Fellowship and Lee A. Dubridge Prize Postdoctoral Fellowship (T. M. S.). CaltechAUTHORS:SQUjfm04 http://resolver.caltech.edu/CaltechAUTHORS:SQUjfm04 http://dx.doi.org/10.1017/S0022112004009309 No commercial reproduction, distribution, display or performance rights in this work are provided. 1312 CaltechAUTHORS Archive Administrator 10 Jan 2006 26 Dec 2012 08:43

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