Chemical control of single bubble cavitation

Abstract

Sonochemistry would be ideally studied with a single bubble with known size pulsating in known acoustic pressure field. Single bubble cavitation provides the means to make such studies. The promise that single bubble cavitation brought to the quantitative measurements of chemical activity of cavitation, however, has not been previously fulfilled due to the very small amount of reacting gas within a single bubble (typically <10–13 moles). We have now quantitated the chemical reactions inside a single cavitating bubble and established an inventory of energy dissipation during bubble collapse. The yields of nitrite ions, hydroxyl radicals, and photons from a single cavitation bubble have now been measured, and the first true measures of energy efficiencies during acoustic cavitation have been determined. The energy efficiency of the formation of hydroxyl radicals from single bubble is comparable to that in multibubble cavitation. The energy efficiency of light emission, however, is much higher for SBSL. The observed rate of nitrite formation is in good agreement with the calculated diffusion rate of nitrogen into the bubble. The temperatures reached during single bubble cavitation in liquids with significant vapor pressures will be substantially limited by the endothermic chemical reactions of the polyatomics inside the collapsing bubble.