Electrification of Sonoluminescing Bubble in Water

Abstract

Previous studies showed that microbubbles in water are negatively charged at the liquid-bubble interface. H+ and OH- in bulk water are considered to be the major factors for the charging mechanism. The electrification of cavitation bubble in water, however, has not been studied. High-temperature and high-pressure conditions inside cavitation bubble lead to chemical reactions producing molecules such as H 2 0 2 and HN0 2 and also to emit light, called sonoluminescence (SL), at bubble collapse. Those chemical reaction products inside bubble diffuse into bulk water. It is suggested that SL bubble interface has different conditions from non-cavitation bubble interface. To clarify electrical property of SL bubble interface is important for understanding the microstructure on the bubble interface and the application of ultrasound-generated bubbles. We investigated, for the first time within our knowledge, the electrification of a SL bubble in water by measuring the translation of bubble under electric field. SL bubble was shifted toward hot electrode when negative voltage was applied as if the bubble received attractive force from the hot electrode. In contrast, SL bubble was shifted to opposite direction when positive voltage was applied as if the bubble received repulsive force from the hot electrode. The results suggested that SL bubble was positively charged in water.