Date of Award

Fall 2013

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical Engineering

First Advisor

Steven T. Wereley

Committee Chair

Steven T. Wereley

Committee Member 1

Xianfan Xu

Committee Member 2

Jun Chen

Committee Member 3

James F. Leary


This dissertation explores various physical mechanisms of the Rapid Electrokinetic Patterning (REP) technique suggested for rapid and precise on-chip manipulation of colloids and fluids, and bio-compatibility of the technique for biological applications. REP is a hybrid opto-electrokinetic technique that is driven by the simultaneous application of an AC electric field and a heating source. It can not only effectively transport and manipulate a fluid but also concentrate and pattern particles suspended in the fluid through the combined effect of an electrohydrodynamic flow, electrostatic colloidal interactions and an electrothermal microfluidic flow. These capabilities make REP a promising tool which can provide significant improvements to the development of many research fields ranging from colloidal science to biotechnology. However, due to its relatively recent invention, the understanding about the roles of each of the REP mechanisms is incomplete. To further understand REP, we analyzed the topology of a typical REP-based particle cluster through development of a Voronoi-Delaunay in-house code and as a result, found that non-equilibrium electric double layer (EDL) polarization is involved in the interaction between the particles as well as

between the particles and the electrode surface. This polarization is a very critical electrokinetic mechanism that determines the stability of REP operation, together with a related phenomenon Maxwell-Wagner interfacial polarization.

The electrothermal microfluidic flow responsible for the transport of particles during REP manipulation also was studied experimentally and theoretically. In the experiments, we measured the whole velocity field and temperature field of the flow using a particle image velocimetry (PIV) technique and a laser-induced fluorescence (LIF) technique. The experiments provided a detailed physical understanding of the various characteristics of the electrothermal flow: 1) three dimensional toroidal flow structure and pattern, 2) dependence on AC frequency, electric potential and temperature rise in a fluid, and 3) relative contribution of natural convection to the flows. On the basis of the comprehensive velocity and temperature data obtained from the experiments, we constructed a dimensionless number to characterize the electrothermal flow using the Buckingham PI theorem. The number consists of an inertial force, a Coulomb force and a dielectric force, and is shown to have a linear relation with the strength of the electrothermal flow.

A complete understanding of the REP mechanisms led to application of the technique for microorganism manipulation. Our study first demonstrated the bio-compatibility of REP using Shewanella oneidensis (S. oneidensis) MR-1, Saccharomyces cerevisiae (S. cerevisiae) and Staphylococcus aureus (S. aureus). A large number of these microorganisms were rapidly concentrated and patterned as well as dynamically manipulated on an electrode surface. Moreover, the precise size-based separation and dynamic/ selective trapping of two different microorganisms also was demonstrated. These abilities of REP can make critical contributions to the realization of a high performance on-chip bioassay system.