A correlation between cavitation bubble temperature, sonoluminescence and interfacial chemistry - A minireview

Abstract

Ultrasound induced cavitation (acoustic cavitation) process is found useful in various applications. Scientists from various disciplines have been exploring the fundamental aspects of acoustic cavitation processes over several decades. It is well documented that extreme localised temperature and pressure conditions are generated when a cavitation bubble collapses. Several experimental techniques have also been developed to estimate cavitation bubble temperatures. Depending upon specific experimental conditions, light emission from cavitation bubbles is observed, referred to as sonoluminescence. Sonoluminescence studies have been used to develop a fundamental understanding of cavitation processes in single and multibubble systems. This minireview aims to provide some highlights on the development of basic understandings of acoustic cavitation processes using cavitation bubble temperature, sonoluminescence and interfacial chemistry over the past 2-3 decades.

Keywords: Acoustic cavitation; Bubble temperature; Interfacial activity; Sonoluminescence; Surface active solutes.

Fig. 1

(A) The dependence of SL intensity, observed at 20 kHz, on thermal conductivity of noble gases [Adapted from Ref [26]]. The insert shows that the cavitation bubble temperature has a linear dependence on the thermal conductivities of gases contained within a cavitation bubble; (B) Relative SL intensity as a function of bubble temperatures observed in a mixture of octanol and dodecane saturated with different noble gases .

Fig. 2

Left. The dependence of SL intensity and bubble temperatures measured by MRR method on the bulk concentration of a surface active solute, ethanol. Frequency. 515 kHz. Right: A schematic representation of SL domain at the centre of a collapsing bubble where peak T is reached. The possibility of the existence of a temperature gradient is proposed .

Fig. 3

Sonoluminescence quenching by a volatile solute in a single bubble (22 kHz) system .

Fig. 4

Schematics showing product buildup over several acoustic cycles .

Fig. 5

Cavitation bubble temperatures measured by MRR method in aqueous solutions containing alcohols at various concentrations [Adapted from Ref [54]]. (355 kHz).

Fig. 6

MBSL quenching as a function of pH in aqueous solutions containing a weak acid or a base . The solid line shows the relative concentration of the ionized form, calculated using Henderson Equation and the solid data points represent experimentally measured SL intensity relative to pure water. Frequency. 515 kHz.

Fig. 7

MBSL behaviour at 20 kHz and 515 kHz in the presence of volatile solutes [Adapted from Ref. [64]].

Fig. 8

SL quenching by propanol could be seen when a plate transducer is used to establish a standing wave and a horn system normally generates transient cavitation where no SL quenching could be observed [Adapted from Ref. [71]].

Fig. 9

MBSL quenching observed at 515 kHz in aqueous solutions containing aliphatic alcohols. Left. The extend of SL quenching increases with an increase in bulk concentration and chain length of the alcohols. Right. SL quenching is a function of surface excess, not bulk concentration, of the alcohols [Adapted from Ref. [61]].

Fig. 10

MBSL quenching at 515 kHz as a function of the chain length of aliphatic alcohols .

Fig. 11

The addition of a charged surfactant results in an increased cavitation activity . Frequency: 515 kHz.