Physical Mathematics Seminar, MIT
September 20, 2005
Title: Induced-Charge Electro-osmosis and Electrophoresis
Speaker: Martin Z. Bazant
Department of Mathematics
MIT
Abstract:
Motivated by the recent discovery of AC electro-osmosis at micro-electrode
arrays, we predict the general phenomenon of "induced-charge
electro-osmosis" (ICEO) -- the slip of a liquid electrolyte at a
polarizable (metal or dielectric) surface when an electric field acts on
its own induced surface charge -- which requires neither AC forcing, nor
electrode surfaces. Building on some earlier Russian work on metal
colloids, we also predict the related effect of "induced-charge
electrophoresis" (ICEP) - the motion of a polarizable particle due to ICEO
flow with broken symmetries, such as partial surface coatings, asymmetric
shapes, and non-uniform applied fields (where "dielectrophoresis" due to
electrostatic stresses must also be considered). We obtain analytical
solutions for simple geometries and solve the general ICEP problem in two
dimensions for any shape and non-uniform field by conformal mapping; more
complicated geometries are studied by numerical methods. Although our
understanding of ICEO is maturing, fundamental questions remain about
"strongly nonlinear" dynamics in large, time-dependent applied fields.
To complement the mathematical theory, we also present novel experiments
demonstrating ICEO in microfluidic devices and discuss applications to
portable (or implantable) microfluidics.