Effects of bovine serum albumin on a single cavitation bubble.

The dynamics and sonoluminescence (SL) of a single cavitation bubble in bovine serum albumin (BSA) aqueous solutions have been experimentally and theoretically investigated. A phase-locked integral imaging has been used to record the bubble pulsation evolutions. The results show that, under the optimum driving condition, the endurable driving pressure, maximum radius, radius compression ratio and SL intensity of the cavitation bubble increase correspondingly with the increase of BSA concentrations within the critical micelle concentration, which indicates that the addition of BSA increases the power capability of the cavitation bubble. In addition, BSA molecules dampen the interfacial motion, and especially the rebounds of the bubble after its collapse. BSA molecules modify the dilatational viscosity and elasticity of the bubble wall. A viscoelastic interfacial rheological model that mainly emphasizes on the description of the bubble wall has been introduced and modified to theoretically explain the measured bubble dynamics. A good consensus between the experimental observation and model calculation has been achieved.

Radial and translational oscillations of an acoustically levitated bubble in aqueous ethanol solutions.

The radial and translational oscillations of a single cavitation bubble in a standing ultrasound wave were investigated experimentally at various driving acoustic pressures for aqueous ethanol solutions with different bulk molar fractions of ethanol range of 0-1.3 × 10(-3). The results show that both the lower and upper stability thresholds of the acoustic driving pressure decreased as the concentration of ethanol was increased. At a given driving pressure the ambient and maximum bubble sizes increased with increasing ethanol concentration. In addition, as the ethanol was increased, the sonoluminescence intensity decreased while the bubble dynamics remained largely unchanged. The translational oscillation of the levitated bubble, however, became increasingly violent with increasing ethanol concentration. The displacement of the bubble reached 0.7 mm at the highest concentration studied (1.3 × 10(-3)) and the maximum bubble size was found to change as the bubble jumped up and down. This bubble translation may be responsible for the decrease of the acoustic driving pressure threshold and suggests that repetitive injection of ethanol molecules into the bubble takes place. These results may account for the different sensitivities of single bubble and multi-bubble sonoluminescence to the presence of volatile additives.

Effect of alcohol on single-bubble sonoluminescence.

The driving parametric regions in frequency-amplitude space and the optimal parameters for single-bubble sonoluminescence (SBSL) in alcohol aqueous solutions are studied systematically by taking measurements of the spectrum and bubble dynamics. The experimental results show that with an increase in alcohol concentration, the region shrinks and shifts. The optimized parameters differ for alcohol solutions having different concentrations, and SBSL driven by fixed parameters dims quickly and is even destroyed immediately with the addition of a small amount of alcohol to pure water. Furthermore, it is seen that the intensity of optimized SBSL decreases as the alcohol concentration increases. The corresponding measurements of the dynamics of the optimized SBSL bubble show that the maximum bubble radius at an alcohol concentration of 1.04 mM is only half that for pure water. Meanwhile, the optimized driving amplitude acquired by direct measurement and that obtained by fitting the radius-time curves with the Rayleigh-Plesset equation both decrease by 12% in the same comparison. Therefore, a decrease in the driving acoustic pressure may be an important reason for the decrease in the optimized SBSL intensity, which should help clarify SBSL mechanisms in alcohol aqueous solutions.