6I-2 Droplet Heating System Based on SAW/Liquid Interaction

In this study, surface acoustic waves (SAW)/lquid interaction (SAW streaming) was used to heat small droplet (2-20 mul). SAW devices were designed on a 128deg rotated Y-cut X-propagating Li-NbO₃ 2" wafer with center frequency of 39.92 MHz. When the droplet is placed on the acoustic path, a longitudinal wave is radiated into the liquid. When SAW amplitude is sufficient, several phenomena can happen such as droplet actuation, internal flow into the droplet, atomisation. Recently, Kondoh et al. have demonstrate that irradiation of droplet by SAW is a powerful technique for heat small amount of liquid. Here, we want to quantify this effect (in static mode) with different droplet volume and a wide range of viscosity as a function of SAW power which is correlated with SAW amplitude. We have worked with a non contact infrared thermometer to measure droplet temperature and in order to explore wide range of viscosity water-glycerol mixture has been used. We notice that more droplet viscosity increase, the higher is the temperature. Finally, the liquid temperature can be controlled by the SAW power. A droplet can be considered as a microreactor because it acts both as a efficient mixer and fluidic thermocycler. This can be interesting for lab on chip