Research Of Single Gas Bubbles Driven By Ultrasound In Water With The Presence Of Surfactant Additives

The surface active additives have pronounced effects on ultrasound cavitation and sonoluminescence (SL). The effects of surfactant include changing the rectified dif-fusion, coalescence, mass exchange and other physical and chemical properties of a cavitation bubble. Moreover, surfactants can be involved into the cavitation bubble and participate in chemical reactions. These effects can cause a change of dynamics and luminescence properties of the cavitation bubble.The radial dynamics and SL of a single cavitation bubble generated by ultrasound in alcohol aqueous solutions with diversified concentrations have been recorded in this thesis. It is observed that, under the optimum driving parameters, with the in-crease of alcohol concentrations, the endurable pressures decrease rapidly, leading to a dampened radial oscillation,viz. the decrease of maximum bubble radius and radius compression ratio, and further contributing to the decrease of SL intensity. However, when conducted under a certain set of driving parameters, with the increase of alco-hol concentrations, maximum radius, radius compression ratio and SL intensities are heavily dependent on the chosen driving parameters. Therefore, the addition of alcohol changes the driving parameter region of a stable SL bubble. It is shown in our experi-mental results that, with the increase of alcohol concentrations, the driving parameter region both shifts and shrinks. Under the low alcohol concentrations, the shift of the parameter region plays a major part in the effects of bubble dynamics and SL. Multi-bubble sonoluminescence (MBSL) is not sensitive to driving parameters, so the shift of diving parameters caused by alcohols in single-bubble system can expound that, to the same extent of SL extinction, the alcohol concentration is much higher in the multi-bubble system than that in single-bubble one. Therefore, through concerning the shift of the driving parameter region of sonoluminescencing bubble, this article supplies an alternative interpretation of the phenomenon that a drop of alcohol can extinguish single-bubble SL immediately. This interpretation is much more reliable for the reason that it is completely based on experiments. Generally, the addition of alcohol weakens the oscillations of a single cavitation bubble, shifts and shrinks the driving parameter region of the SL bubble, thus changing the characteristics of dynamics and SL of the cavitation bubble.Furthermore, this thesis reports the dynamics and SL of a single cavitation bub-ble in BSA (bovine serum album) aqueous solutions. BSA molecules adsorb on the gas-water surface of a cavitation bubble due to its hydrophobility, thus modifying di-latational viscosity and elasticity of the interface. In order to accurately characterize and analyze the dynamics of the single cavitation bubble, the viscoelastic interfacial rheological model that mainly concentrates on the description of interfacial surface has been applied. The model proves appropriate and suitable for our experiments. The results show that, under the optimum driving parameters, with the increase of BSA concentrations, the endurable pressures, maximum radius, radius compression ratio and SL intensities of the cavitation bubble increases correspondingly, which indicates that the addition of BSA increases the power capability of the cavitation bubble. In ad-dition, BSA can hinder the interfacial motion; the first rebound radius of the cavitation bubble decreases with the increase of BSA concentrations.In the end, we study the effects of Tween20on a single cavitation bubble. It is found that, under low driving pressure, the cavitation bubble translates vehemently with very low Tween20concentrations, as we increase driving pressure, the bubble can not be captured at all. We attribute the instability of the cavitation bubble to the reason that Tween20molecules adsorb on the bubble wall and tremendously increase the interfacial mobility, greatly decreasing the surface tension at the same time.