Sonoluminescence and sonochemistry in aqueous solutions containing surface active solutes

Abstract

The ultrasound induced reduction of gold chloride in aqueous alcohol solutions has been measured and compared with the extent of sonoluminescence (SL) quenching observed in the same solutions, as a function of alcohol concentration. Both ultrasound initiated phenomena were found to be directly related to the Gibbs surface excess concentration of the alcohol at the gas/water interface. The SL quenching occurs in two distinct surface excess regimes. The first region accounts for about 90% quenching of the SL signal. The second quenching region extends over a broader surface excess range and the profile matches the extent of enhancement in the reduction of gold chloride. When the nonvolatile surfactant sodium dodecylsulfate (SDS) was used instead of alcohol, the trends in the SL signal and in the sonochemical reduction process were quite different. At low concentrations (<2 mM) of SDS, the SL signal was enhanced over that obtained from water without surfactant. At higher SDS concentrations, the SL signal declined and leveled off to about 80% of the water signal at about 10 mM. In contrast, the reduction of gold chloride increased to about 8 mM SDS and then remained constant above this value. Possible mechanisms that explain the results will be presented.