Application Study Of The Light-driven Micro Flows

With optical theory continuously enriched and improved, applications of light in human life and technologies have been being increasingly developed. Due to a series of advantages and characteristics of the laser, studies of laser in both fundamental physics and its applications are attracting more and more interests from researchers. Recently, it has been found that irradiation of an infrared laser can push directional flows within a liquid film floating on another immiscible liquid. In this work, the behaviors of these light-driven liquid flows were studied systematically using particle image velocimetry (PIV) technique. Compared to traditional particle velocity measurement techniques, PIV features no disturbance, high precision, broad range of measurement, and contactless etc. Using PIV, the images of moving the tracer particles within the flow field can be acquired via the illumination system and the CCD camera. Then, the velocity distribution of the flow field can be obtained by analyzing the correlation of the successive images using PIVview2C software. The advantages of the PIV technology are:(1) it can avoid the interference from the instrument, which normally happens with traditional particle velocity measuring techniques; (2) the velocity maps of the whole flow field can be obtained directly through the PIV analysis. In the recent decades, PIV technology has encountered a rapid development. It can be used to study both 2d and 3d flow fields in liquid. It has become an important technology for measurement of flow field.The phenomena studied in this work are found to occur only in the liquid films of asymmetric thickness. For the decane-water layered liquid system of two mutually inverse geometries studied, experimental results show that these IR-driven flows always flow toward the direction along which the decane film becomes thinner. The structure and behaviors of these micro flows were systematically studied here. In results, the liquid flow rate increases as the laser power increases, and decreases as the liquid film becomes thicker. After Tween 80 (a surfactant) was added in water to reduce the room-temperature decane-water interfacial tension, the flow rate will decrease. In structure and behaviors, these liquid flows cannot be interpreted as driven by Marangoni’s mechanism. Thus, it is believed that these flows are driven by another completely different thermodynamic mechanism. Both the pattern and the direction of the flows predicted in this newly-proposed theory show good agreement with those observed in experiment. The scale of order of flow speed theoretically predicted also agrees with that experimentally observed. These phenomena of directional motion of liquid film can be potentially employed in micro-fluidic and micro-mechanical technologies, with a great practical significance for the development for future micro-actuation systems.