The transition from induced charge electroosmotic flow to electrothermal flow in a constriction microchannel

Electric field is the method of choice in microfluidic particle-handling devices because of the precise transport and placement of particles via fluid electroosmosis and particle electrophoresis. Insulator-based dielectrophoretic microdevices have been increasingly used for particle manipulation purposes, where insulating structures are exploited to create electric field gradietns for the dielectrophoretic focusing, trapping and separation etc. However, the presence of the insulating strucutres, especially those with sharp edges, may influence the linear electroosmotic fluid low by two nonlinear electrokinetic phenomena: induced charge electroosmotic flow and electrothermal flow. We present a combined experimental and numerical study of the transition from the induced charge electroosmotic flow in a low-conductivity fluid to the electrothermal flow in a high-conductivity fluid. A parametric study is also conducted to understand these two nonlinear electrokinetic phenomena competing with one another in the transition fluid conductivities.