Mechanoluminescence from Acoustic Cavitation

The external effects of acoustic cavitation- the formation, expansion, and implosive collapse of bubbles in liquids irradiated with ultrasound- include turbulent flow, shock waves, and microjetting. To study these effects we have looked at mechanoluminescence (ML): light produced during any mechanical action on a solid. We report for the first time the ML of sucrose and resorcinol induced by acoustic cavitation in alkanes. The spectra of ML induced by cavitation resemble other sources of ML but with more intense gas discharge relative to the crystal luminescence. It is known that as the strength of the mechanical action on the solid is increased the intensity of the gas discharge increases; this gives evidence of the extreme external effects of cavitation. We have also observed other discharge products not seen before in ML including CH, C2, and CO (when oxygen is present). The effect of liquid vapor pressure (VP) has also been studied; as lower VP liquids are used the ML intensity of the gas discharge increases. In high VP liquids no helium gas discharge is observed, but with very low VP liquids the gas discharge is very intense.