Implosion, ultrasonic waves

Sonochemistry (chemical events induced by exposure to ultrasound) occupies an important place in organic chemistry. The chemical effects of high-intensity ultrasound were extensively smdied in aqueous solutions for many years, but is now applied to a variety of organic solvents. The origin of sonochemistry is acoustic cavitation the creation, growth, and implosive collapse of gas vacuoles in solution by the sound field. Acoustic cavitation is the phenomenon by which intense ultrasonic waves induce the formation, oscillation, and implosion of gas... 

Ultrasonic wave clearly enhances the solubilization process (Figure 7, 8). Figure 8 also indicates that diffusion-controlled dissolution maintained even under ultrasonic pulses. The diffusivity under ultrasonic pulses was measured to increase about 3-4 times at the given geometry and power used in this experiment. There are two known effects of ultrasonic waves on solubilization i) acoustic streaming, and ii) cavitation/implosion[24,25]. 

QCM technique can supply in-situ kinetics of the reaction inside the cell. Solubilization of Cu(acac)2 L/SC CO2 was diffusion-controlled. Difftisivities of Cu(acac)2 in L/SC CO2 were also obtained. Ultrasonic waves enhance dissolution of Cu(acac)2 in CO2 mainly due to acoustic streaming. Cavitation/implosion in L/SC CO2 does not occur as often as in water. 

Scission Kinetics. The kinetics of ultrasonic scission can be directly ascribed to the implosion velocity of the cavitation bubbles and the polymer that is fractured. The scission rate and the limiting molecular weight are thus influenced by the ultrasonic wave, the solvent properties, and the polymer structure. 

Energy of cavitation implosion (temperature, pulse height of ultrasonic wave)... 

Liquids irradiated with ultrasound can produce bubbles. These bubbles oscillate and grow a little more during the expansion phase of the sound wave than they shrink during the compression phase. Under the proper conditions these bubbles can undergo cavitation, violent bubble collapse or implosion, leading to droplets particle size reduction. The use of ultrasonication in emulsification is more efficient than rotor-stator systems. 

Sonifiers and ultrasonic baths have been used to improve the level of intercalation and exfoliation particularly for in-situ polymerised nanocomposites (Artzi et al, 2002 Liao et al, 2001 Okamoto et al, 2000). If a sound wave is of sufficient energy, cavitation bubbles are created at sites of rarefaction as the liquid fractures or tears because of the negative pressure of the sound wave in the liquid. As the wave fronts pass, the cavitation bubbles can eventually grow to be unstable under the influence of positive pressure. The high-speed collapse of the cavitation bubbles results in implosions, which cause shock waves to be radiated from the sites of the collapse. High temperatures and pressures can be generated at the implosion sites of cavitation bubbles. 

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