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Anisotropic electro-osmotic flow over super-hydrophobic surfaces

Published online by Cambridge University Press:  11 February 2010

SUPREET S. BAHGA ,
OLGA I. VINOGRADOVA  and
MARTIN Z. BAZANT
SUPREET S. BAHGA
Affiliation:
Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA
OLGA I. VINOGRADOVA
Affiliation:
A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31 Leninsky Prospect, 119991 Moscow, Russia
MARTIN Z. BAZANT*
Affiliation:
Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA Departments of Chemical Engineering and Mathematics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
*
†Email address for correspondence: [email protected]
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Abstract

Patterned surfaces with large effective slip lengths, such as super-hydrophobic surfaces containing trapped gas bubbles, have the potential to greatly enhance electrokinetic phenomena. Existing theories assume either homogeneous flat surfaces or patterned surfaces with thin double layers (compared with the texture correlation length) and thus predict simple surface-averaged, isotropic flows (independent of orientation). By analysing electro-osmotic flows over striped slip-stick surfaces with arbitrary double-layer thickness, we show that surface anisotropy generally leads to a tensorial electro-osmotic mobility and subtle, nonlinear averaging of surface properties. Interestingly, the electro-osmotic mobility tensor is not simply related to the hydrodynamic slip tensor, except in special cases. Our results imply that significantly enhanced electro-osmotic flows over super-hydrophobic surfaces are possible, but only with charged liquid–gas interfaces.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 644 , 10 February 2010 , pp. 245 - 255
Copyright
Copyright © Cambridge University Press 2010

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