Modeling Electrokinetics with Applications to Micro and Nano Fluidic Systems

Hui Zhao
Ph.D. Candidate
Advisor: Professor Haim H. Bau
Mechanical Engineering and Applied Mechanics
University of Pennsylvania

Abstract
With the rapid growth in lab-on-a-chip technology, the prospects of detecting viruses on a microfluidic diagnostic device or immobilizing single bio-molecules have become more and more promising. This imposes a big challenge for fluid manipulation such as propulsion, mixing and particle manipulation, which are far from trivial due to the low Reynolds number of the flow. Electrokinetics provides an opportunity to fulfill this task, with advantages as easily fabricated inexpensive devices that consume minimal power. After briefly discussing the fundamentals of electrokinetics, this talk will focus on two applications of the phenomena in micro/nano systems. First, a novel active chaotic stirrer is proposed to enhance mixing. The stirrer consists of a conducting cylinder and four electrodes. The conducting cylinder generates an induced charged electro-osmotic flow under the action of the electric field and stirring is achieved by systematically alternating the electric field in time. I also extend the application of electrokinetics to chromatography. I derive a mathematical model to calculate the dispersion coefficient in the presence of secondary flow. Also, a novel dispersion reduction strategy is realized by imposing a secondary or transverse flow, driven by DC electro-osmosis or AC electro-osmosis, that is independent from the primary flow. This work will guide the design of an efficient liquid chromatography device.