Acoustics cavitation in microfluidics for sonoluminescence and sonochemistry

Abstract

Strong ultrasound is applied to a microfluidic channel to generate nonlinear surface waves which entrap bubbles at the gas–liquid interface to form oscillating bubbles. The ultrasound is generated by the piezoelectric transducer on the side of polydimethylsiloxane microchannel. The microchannel is attached to a glass slide through plasma bonding, while the transducer is glued by epoxy for strong coupling. The high speed photography shows that continuous cavitation clusters are formed within the microchannel as gas is injected. As they collapse rapidly, they are able to produce very intense concentration of energy that is able to emit light. This phenomenon is known as sonoluminescence. Previously, sonoluminescence is achieved via a single bubble or multiple bubbles in a bulk liquid. The authors report a realization of sonoluminescence in a microfluidic device. The same oscillating bubbles can also be used as micro-labs. They can trigger chemical reactions that require high temperature and pressure. We achieve the formation of OH radicals in a lab-on-a-chip device. In conclusion, nonequilibrium microbubbles can be induced in a microfluidic system. They oscillate and collapse, and in the process provide a source of energy concentration for the emission of light and the activation of chemical reactions.