Velocity Fields in Opto-Electrically Induced Fluid Flows

In this paper we demonstrate opto-electrothermal pumping in a very simple setup consisting primarily of parallel electrodes and explore the characteristics of such flows with different optical intensity patterns. For our parallel electrode configuration setup, ITO-coated electrodes were used to generate electric fields. The optical illumination system uses a focused laser beam 1,064nm, continuous mode. The experiments are analyzed in terms of existing analytical models for electrothermal flows. Microvortices created using the electric field and optical illumination resembles a sink/source type flow with the laser spot as the center of the sink/source. The flow velocity is characterized as a function of the AC signal frequency and the strength of electric field. At larger frequencies (f > 1 MHz), the velocity of the vortices decreases and around f > 5 MHz, Brownian motion is more dominant than the vortices. The line illumination is created by holographically stretching the point illumination. The line is about 28 μm in length. Result of this experiment is determined by means of visualization only. The creation of these vortices can not only be used to create microfluidic pumps but also also show immense promise as microfluidic mixers without utilizaing any invasive components.