טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentZehavi Matan
SubjectNonlinear Induced-Charge-Electro-Osmotic Flow around a
Microchannel Corner
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Gilad Yossifon
Full Thesis textFull thesis text - English Version


Abstract

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:

[1]           M. Zehavi and G. Yossifon, Particle dynamics and rapid trapping in electro-osmotic flow around a sharp microchannel corner, Phys. Fluids, 26, 082002 (2014).

[2]           M. Zehavi, A. Boymelgreen and G. Yossifon, Competition between Induced-Charge Electro-Osmosis and Electro-Thermal Effects around a Weakly-Polarizable Microchannel Corner, submitted.