Suppression of sonochemiluminescence reduction at high acoustic amplitudes by the addition of particles.

The effect of particle addition to a liquid or liquid surface on the sonochemiluminescence (SCL) was investigated using a luminol aqueous solution under ultrasonic treatment at 154 kHz. The acoustic-amplitude dependence of the SCL intensity was measured, in addition to capturing images of luminescent spatial patterns. At higher acoustic amplitudes, the cavitation efficiency dramatically reduces. This behavior is suppressed in the presence of particles. Particle addition provides nucleation sites for cavitation bubbles, lowering the cavitation threshold, and weakening the liquid surface vibration as the pressure amplitude decreases. It is shown that the reduction in SCL is suppressed under the addition of alumina particles into luminol aqueous solution. As the amount of alumina particles increases, the range of acoustic amplitude for suppressing the reduction in SCL is enlarged toward high amplitude, and the intensity of the SCL increases. Simultaneous addition of alumina particles into the solution and hydrophobic polytetrafluoroethylene (Teflon) particles onto the liquid surface is also effective. Examination of SCL images revealed that alumina particles added to the liquid at high acoustic amplitude caused the entire region of the reaction volume to be homogeneously luminous. If hydrophobic particles cover the solution surface, the surface vibration at high acoustic amplitude is fixed and the sound field becomes stable. This is responsible for suppression of the reduction in SCL and leads to a high rate of sonochemical reaction, even at high acoustic amplitude.