The effect of surface active solutes on bubbles exposed to ultrasound

A review of the effects of a range of surface active solutes, aliphatic alcohols, alkyl amines, carboxylic acids and surfactants on bubbles exposed to ultrasound is presented. The solutes are shown to affect the phenomenon of sonoluminescence (SL) in quite a number of different ways. Ionic surfactants have a strong influence on interbubble interactions which at low concentrations (1 mM) results in an enhancement in SL. Alcohols and the neutral forms of the organic acids and amines induce SL quenching. The SL quenching is attributed to the formation and accumulation of decomposition products in the hot core of an oscillating bubble resulting from the evaporation of volatile solute adsorbed at the bubble interface. Some results are presented on the influence of low concentrations of alcohol on the SL generated from a single bubble and on the bubble dynamics, when exposed to ultrasound. These results add support to the interpretation given for solute-induced effects observed in multibubble systems. It is also shown that SL can be used as an internal light source to excite aromatic solutes that subsequently fluoresce, a process referred to as sonophotoluminescence.