The effect of pH on multibubble sonoluminescence from aqueous solutions containing simple organic weak acids and bases

The sonoluminescence (SL) intensity from aqueous solutions: containing either all;yl acids or alkylamines is shown to be dependent on both the hydrocarbon chain length of the solute and the pH of the solution. Alkylamines quench the SL only at pH values above about 9 whereas alkyl acids quench only below about pH 7. In the pH ranges where SL quenching occurs, the longer the alkyl chain length the greater the effect. The results have been interpreted in terms of the neutral forms of the solutes adsorbing at the bubble/solution interface and then evaporating into the bubble core during its growth and compression oscillations, leading to the quenching of the SL. Possible processes that may be responsible for the quenching are discussed.