Induced-charge electrokinetics at large voltages

The classical transport theory cannot explain the experimental behavior of electrochemical systems in the extreme operating conditions required by modern microfluidics devices. Some experimental puzzles include strange behavior of colloidal particles, high-frequency flow reversal in microfluidic ACEO pumps, and concentration dependence of electrokinetic slip. Theoretical developments would help not only in exploiting poorly understood effects favorably, but also in building more efficient microfluidics devices. The goal of this thesis is to explore possible mechanisms and modifications of the current theory that would enable us to interpret the experimental data. The following is a brief summary of the contributions of this thesis to the subject: Colloidal Particles. A new invention in colloidal science is the Janus particle, which is a two-faced spherical particle where one face is polarizable, and the other non-polarizable. These particles have potential applications in drug delivery, building of nanowires and solar energy. Experiments show that Janus particles strongly interact with boundaries: they approach walls, swim along walls, or sometimes jump away from walls. We show, by conducting numerical simulations of this truly 3D problem, that at least some of those observations can be explained within the classical linear theory. Finite Size Effects in Electrolytes. The classical Poisson-Boltzmann (PB) theory of electrolytes assumes a dilute solution of point charges with mean-field electrostatic forces. Even for very dilute solutions, however, it predicts absurdly large ion concentrations (exceeding close packing) for surface potentials of only a few tenths of a volt, which are often exceeded, e.g., in microfluidic pumps and electrochemical sensors. Since the 1950s, there have been numerous attempts in the literature to incorporate steric effects into the standard models.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mathematics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Kilic, Mustafa Sabri

Advisor dc:contributor.advisor

• Matin Z. Bazant.

• Mathematics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/45346

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/45346