Water vapor and sonoluminescence

Abstract

In recent work, it has been shown that segregation of gas mixtures within sonoluminescence bubbles is driven by strong thermal and pressure gradients inside the bubble [B. D. Storey and A. J. Szeri, ‘‘Mixture segregation within sonoluminescence bubbles,’’ in review]. Although these rather exotic types of diffusive transport are often neglected, they are of crucial importance in a number of applications. These effects conspire to increase the fraction of the lighter gas in a mixture of noble gases near the center, and to increase the fraction of the heavier gas near the bubble wall at the moment of extreme collapse. This results in a greater energy concentration at the bubble center. While the temperature and pressure peaks have a duration (FWHM) of only a few hundred picoseconds at most, it has been found that appreciable mixture segregation persists for several orders of magnitude longer. Armed with this new understanding of how gas mixtures behave, it is possible to investigate more deeply the question of water vapor within the bubble. Several investigators have shown that the presence of water vapor has important consequences for compression versus shock heating, for hydrodynamics of the bubble collapse, and for chemistry.