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Bubble dynamics, sonoluminescence, and sonochemistry

Starting with my PhD work at UC Berkeley, I began working on the problem of what happens inside micron sized gas bubbles that are forced with strong acoustic fields. Bubbles are very non-linear oscillators and characteristic motions are slow expansions folowed by rapid collapses. Collapses can be so rapid that the gas inside the bubble is significantly compressed and can become hot enough to emit light. For several years, the mechanism of the light emission was widely debated as was the maximum acheivable temperatures inside the bubble. Early estimates predicted strong shock waves that resulted in temperatures over 1,000,000 K; generating much excitement that there may be exotic physics inside these simple bubbles. If you are interested in some of the early excitement, see the article; "Sonoluminescence: Sound into Light", Scientific American, February 1995, Vol. 272 Issue 2, p46. Or watch a really bad movie about sonoluminescence starring Neo.

Our scientific work (not the science fiction movies) investigated the role of water vapor in bubble dynamics. We conducted direct numerical simulations of the compressible Navier Stokes equations accounting for multi-species transport and chemical reactions inside the bubble. We found that water was trapped inside the bubble by molecular diffusion. The amount of trapped water vapor was much higher than the amount that would be present if diffusion were not present - an assumption that was implicit in most of the theoretical work at the time. This trapped vapor and the subsequent endothermic chemical reactions predicted significantly lower collapse temperatures (~6,000 K) than if the water vapor was neglected in the models (~30,000 K or higher). One of the interesting aspects of sonoluminescence is that the bubbles are less than a micron in size and collapse occurs over nano-seconds; detailed measurements are very difficult. Therefore, it took several years for theory, computation, and experiment to come together to provide reasonable explanations of the phenomena. An excellent review article of sonoluminescence was written by Brenner, Hilgenfeldt, and Lohse for Review of Modern Physics in 2002.

In 2002 it was reported in Science that researchers had measured evidence of nuclear reactions due to bubble collapses. That work generated much press and was widely debated. As of yet, no other researchers have been able to reproduce these results. There is still no firm agreement on how hot bubbles can become upon collapse, though I beleive that most researchers have settled somewhere between 5,000 K and 15,000 K. These temperatures are consistent with excellent measurements made by Ken Suslick's group at the University of Illinois and reported in Nature in 2005.

A few years ago (~2001), I wrote this Introduction to sonochemistry to describe my research interests and projects at the time. The document may be a little out of date, but the background should still generally be valid. More detail on my work can be found in the publications listed below.

Collaborators: Andrew Szeri, UC Berkeley.

Related publications

Szeri, A.J., Storey, B.D., Pearson, A. & Blake, J. 2003 Heat and mass transfer during the violent collapse of non-spherical bubbles. Physics of Fluids,15, 2576-2588.
Storey, B.D. & Szeri, A.J. 2002 Argon rectification and the cause of light emission in single bubble sonoluminescence. Physical Review Letters. 88 074301.
Lin, H., Storey, B.D., & Szeri, A.J. 2002 Rayleigh-Taylor instability of violently collapsing bubbles. Physics of Fluids,14, 2925-2928.
Lin, H., Storey, B.D., & Szeri, A.J. 2002 Inertially driven inhomogenieties in violently collapsing bubbles: the validity of the Rayleigh-Plesset equation. Journal of Fluid Mech. 452, 145-162.
Matula, T.J., Hilmo, P.R., Storey, B.D., & Szeri, A.J. 2002 Radial response of individual bubbles subjected to shock wave lithotripsy pulses in vitro. Physics of Fluids. 14, 913-921.
Storey, B.D. Shape stability of sonoluminescence bubbles: a comparison of theory to experiments. Physical Review E. 64, 017301.
Storey, B.D. & Szeri, A.J. 2001 A reduced model of cavitation physics for use in sonochemistry. Proceedings of the Royal Society A. 457 1685-1700.
Storey, B.D. & Szeri, A.J. 2000 Water vapour, sonoluminescence and sonochemistry. Proceedings of the Royal Society A. 456, 1685-1709.
Storey, B.D. & Szeri, A.J. 1999 Species segregation in sonoluminescence bubbles. Journal of Fluid Mechanics. 396. 203-221.