Fundamental Study of Nonlinear Electrokinetic Phenomena in Insulator-based Dielectrophoretic Microdevices

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Dielectrophoresis (DEP) is very useful in manipulating micro/nano-sized particles (e.g., cells, beads, viruses, DNA and protein molecules). Insulator-based dielectrophoresis (iDEP) exploits insulating structures, such as hurdles, posts and ridges, to trap, concentrate, separate and sort particles. Compared to the traditional electrode-based dielectrophoresis (eDEP), iDEP microdevices have the advantages of easy fabrication and robust performance. However, the presence of in-channel insulating structures cause two phenomena that may strongly disturb the flow and either suppress or enhance the particle manipulation in iDEP microdevices. These phenomena are: the electrothermal flow due to the amplified Joule heating in the fluid around the insulators, and the induced charge electroosmotic (ICEO) flow due to the electrical polarization of the insulators. An accurate understanding of either phenomenon is significantly complicated by the thermal diffusion or electric field leakage that occurs in the entire device. This project seeks to develop a generalized depth-averaged model for the fundamental study of nonlinear electrokinetic phenomena in iDEP microdevices. The proposed model will substantially reduce the computational cost for predicting the particle manipulation performance in iDEP devices. It will also serve as an efficient and accurate tool for the optimal design and control of a wide class of electrokinetic microfluidic devices with shallow-channel geometries. This research will be intimately weaved into the undergraduate and graduate educations at Clemson University and the high school outreach in South Carolina. Undergraduate and high school students will be actively involved through various programs available in the department, university, and state with emphasis on the inclusion of women and underrepresented minorities. This project will be the first comprehensive fundamental study of nonlinear electrokinetic phenomena in iDEP microdevices. It is hypothesized that the nonlinear ICEO and electrothermal flows are dominant in low and high ionic concentration fluids, respectively, and can suppress each other in an intermediate ionic concentration fluid. An asymptotic analysis of the temperature-coupled heat, fluid and charge transport equations will be performed for electrokinetic flow in shallow microchannels. A depth-averaged model will be developed based on the asymptotic analysis to simulate the development of temperature, flow and electric fields in typical iDEP microdevices with consideration of both Joule heating and induced charge effects. The fluid temperature and velocity fields will be measured near the insulating structures. The validity of the developed depth-averaged model will be assessed by comparing its predictions with both 3D full-scale numerical simulations and experimental data. The acquired fundamental knowledge of nonlinear electrokinetic phenomena will establish a heat transfer and fluid mechanics framework for iDEP microdevices.