|M.Sc Student||Zehavi Matan|
|Subject||Nonlinear Induced-Charge-Electro-Osmotic Flow around a|
|Department||Department of Mechanical Engineering||Supervisor||Professor Gilad Yossifon|
|Full Thesis text|
This research focuses on non-linear electrokinetic phenomena around a microchannel corner, mainly fluid and particle behavior under high externally applied electric fields. The main phenomenon studied is induced charge electro-osmosis (ICEO). This non-linear phenomenon emanates from dielectric polarization of the dielectric wall, creating a unique ejection flow pattern at the corner. A microchannel flow system was fabricated using soft lithography techniques and used to explore the phenomenon experimentally.
Interesting effects for a DC external forcing, such as asymmetry of the flow upon reversal of electric field polarity, particle accumulation at the corner vicinity and down-stream vortex flow patterns were experimentally observed. Analytical and numerical models were developed, accounting for the unique vortex flow patterns of combined ICEO flow and linear electro-osmotic flow (EOF), as well as particle dynamics from electrophoresis (EP) and dielectrophoresis (DEP) acting on tracer particles in the flow.
Experimental results by means of micro-particle-image-velocimetry (μPIV) for AC external forcing yield quantitative evaluations of ICEO ejection velocity and frequency response. At highly conductive electrolyte solutions competition between ICEO and electro-thermal effects stemming from joule heating are observed. These observations were analyzed by numerical simulations combining electrical, thermal and hydrodynamic analysis. The thermal model results were verified by a temperature visualization experiment.
This study generated the following two publications which appear in the appendixes and hence allows us to significantly shorten the main body of the thesis text:
 M. Zehavi and G. Yossifon, Particle dynamics and rapid trapping in electro-osmotic flow around a sharp microchannel corner, Phys. Fluids, 26, 082002 (2014).
 M. Zehavi, A. Boymelgreen and G. Yossifon, Competition between Induced-Charge Electro-Osmosis and Electro-Thermal Effects around a Weakly-Polarizable Microchannel Corner, submitted.