Cavitation bubbles sonoluminescence

The phenomenon of acoustic cavitation results in an enormous concentration of energy. If one considers the energy density in an acoustic field that produces cavitation and that in the coUapsed cavitation bubble, there is an amplification factor of over eleven orders of magnitude. The enormous local temperatures and pressures so created result in phenomena such as sonochemistry and sonoluminescence and provide a unique means for fundamental studies of chemistry and physics under extreme conditions. A diverse set of apphcations of ultrasound to enhancing chemical reactivity has been explored, with important apphcations in mixed-phase synthesis, materials chemistry, and biomedical uses. 

Suslick KS, Flannigan DJ (2008) Inside a collapsing bubble Sonoluminescence and the conditions during cavitation. Ann Rev Phys Chem 59 659-683... 

Weninger KR, Camara CG, Putterman SJ (2001) Observation of bubble dynamics within luminescent cavitation clouds sonoluminescence at the nano-scale. Phys Rev E 63 016310... 

Spectroscopic Probes of Cavitation Conditions. Determination of the temperatures reached in a cavitating bubble has remained a difficult experimental problem. As a spectroscopic probe of the cavitation event, MBSL provides a solution. High resolution MBSL spectra from silicone oil under Ar have been reported and analyzed (7). The observed emission comes from excited state C2 and has been modeled with synthetic spectra as a function of rotational and vibrational temperatures, as shown in Figure 7. From comparison of synthetic to observed spectra, the effective cavitation temperature is 5050 =L 150 K. The excellence of the match between the observed MBSL and the synthetic spectra provides definitive proof that the sonoluminescence event is a thermal, chemiluminescence process. The agreement between this spectroscopic determination of the cavitation temperature and that made by comparative rate thermometry of sonochemical reactions is surprisingly dose (6). 

It is well known that when acoustic waves are generated in aqueous and other media luminescence can be observed [205], This type of luminescence is known as sonoluminescence and has been attributed to the process of cavitation during which bubbles are formed. The collapse of these cavitation bubbles during the compression portion of the sound wave represents a very high energy output which results... 

Recent studies, especially of sonoluminescence (Ch. 1), have led to questions about the existence of a cold plasma inside the cavitation bubbles. In the usual definition, a cold plasma is an ionized state of matter in which the molecules have a temperature below a few himdred K, but the electronic temperature reaches several thousand K. The existence of ionized species in the bubbles and their implication at some stage of the reaction s initial step would make sonochemistry more or less similar to the chemistry in mass spectrometers, with consequences on the modeling and prediction of the reactivity. 

Fig. 1.1 Schematic representation [Adapted from Ref. 41] of pulsed sonoluminescence technique to determine the resonance size of cavitation bubbles. Bubbles grow during pulse on (T) and dissolve during pulse off (To). With increasing T , steady-state SL intensity decreases top right) eventually to zero—the corresponding To is used to calculate the bubble size using Eq. 1.3...

Tmax—bubble temperature on collapse T , and are solution temperature and pressure, respeetively, Py is pressure inside the bubble and y is heat capacity ratio of the gas inside the bubble. A theoretical temperature of about 12,700 K could be calculated by using y = 1.66 (ideal gas), T , = 298 K, P , = 2 atm, Py = 0.031 atm. Replacing y of an ideal gas by that of water (1.32), the temperature drops to 6150 K highlighting the importanee of the heat capacity ratio of the gas contained in the collapsing bubbles. Susliek and coworkers [46, 47] have used sonoluminescence spectra to calculate bubble temperatures in multibubble systems and found to be in the order of 1000-5000 K. Henglein and coworkers [48] have used methyl radical recombination method and determined the cavitation bubble temperatures to be in a... 

Multi-bubble sonoluminescence (MBSL) Emission of light from a cloud of cavitating bubbles formed during ultrasonic irradiation of a liquid. 

Single-bubble sonoluminescence (SBSL) Emission of light from a single cavitating bubble in a liquid, usually water. 

There are two types in acoustic cavitation. One is transient cavitation and the other is stable cavitation [14, 15]. There are two definitions in transient cavitation. One is that the lifetime of a bubble is relatively short such as one or a few acoustic cycles as a bubble is fragmented into daughter bubbles due to its shape instability. The other is that bubbles are active in light emission (sonoluminescence (SL)) or chemical reactions (sonochemical reactions). Accordingly, there are two definitions in stable cavitation. One is that bubbles are shape stable and have a long lifetime. The other is that bubbles are inactive in SL and chemical reactions. There exist... 

McNamara WBI, Didenko YT, Suslick KS (1999) Sonoluminescence temperatures during multi-bubble cavitation. Nature 401 772-775... 

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