Condensed Matter Theory Seminar
Harvard University
May 3, 2007

Induced-Charge Electro-osmosis

Martin Z. Bazant
Department of Mathematics and
Institute of Soldier Nanotechnologies
MIT

Abstract: 

"Electro-osmosis" refers to the flow of an electrolyte (salt solution)
past a charged surface driven by an electric field; the associated
motion of a suspended particle is "electrophoresis". For the past
century, it has mostly been assumed that the surface charge is fixed
at its equilibrium value, which amounts to a linear response
theory. This talk describes the nonlinear phenomenon of
"induced-charge electro-osmosis'' (ICEO), where the field acts on its
own induced charge near a polarizable surface. New examples will be
given of surprising motions of anisotropic particles and fast
low-voltage pumping by electrode arrays, which could enable tiny
portable or implantable microfluidic devices.  In each case,
experiments have confirmed basic theoretical predictions, while also
revealing puzzling phenomena, such as the decay of ICEO flow at high
salt concentration. This leads to a fundamental open question: what is
the nonlinear response of an electrolyte to a large applied voltage
(>> kT/e = 25 mV)? The challenge is to describe the dynamics of 
ions and solvent crowded near a highly charged surface.