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Electrically Driven Flow near a Colloidal Particle Close to an Electrode with a Faradaic Current
 

Summary: Electrically Driven Flow near a Colloidal Particle Close to an
Electrode with a Faradaic Current
W. D. Ristenpart, I. A. Aksay, and D. A. Saville*
Department of Chemical Engineering, Princeton UniVersity, Princeton, New Jersey 08544
ReceiVed September 30, 2006. In Final Form: December 5, 2006
To elucidate the nature of processes involved in electrically driven particle aggregation in steady fields, flows near
a charged spherical colloidal particle next to an electrode were studied. Electrical body forces in diffuse layers near
the electrode and the particle surface drive an axisymmetric flow with two components. One is electroosmotic flow
(EOF) driven by the action of the applied field on the equilibrium diffuse charge layer near the particle. The other
is electrohydrodynamic (EHD) flow arising from the action of the applied field on charge induced in the electrode
polarization layer. The EOF component is proportional to the current density and the particle surface (zeta) potential,
whereas our scaling analysis shows that the EHD component scales as the product of the current density and applied
potential. Under certain conditions, both flows are directed toward the particle, and a superposition of flows from two
nearby particles provides a mechanism for aggregation. Analytical calculations of the two flow fields in the limits
of infinitesimal double layers and slowly varying current indicate that the EOF and EHD flow are of comparable
magnitude near the particle whereas in the far field the EHD flow along the electrode is predominant. Moreover, the
dependence of EHD flow on the applied potential provides a possible explanation for the increased variability in
aggregation velocities observed at higher field strengths.
Introduction
Situations in which electric fields induce fluid motion are

  

Source: Aksay, Ilhan A. - Department of Chemical Engineering, Princeton University

 

Collections: Materials Science