Sonochemistry

In chemistry, the study of sonochemistry is concerned with understanding the effect of ultrasound in forming acoustic cavitation in liquids, resulting in the initiation or enhancement of the chemical activity in the solution. Therefore, the chemical effects of ultrasound do not come from a direct interaction of the ultrasonic sound wave with the molecules in the solution. The simplest explanation for this is that sound waves propagating through a liquid at ultrasonic frequencies do so with a wavelength that is significantly longer than that of the bond length between atoms in the molecule. Therefore, the sound wave cannot affect that vibrational energy of the bond, and can therefore not directly increase the internal energy of a molecule. Instead, sonochemistry arises from acoustic cavitation: the formation, growth, and implosive collapse of bubbles in a liquid. The collapse of these bubbles is an almost adiabatic process, thereby resulting in the massive build-up of energy inside the bubble, resulting in extremely high temperatures and pressures in a microscopic region of the sonicated liquid. The high temperatures and pressures result in the chemical excitation of any matter that was inside of, or in the immediate surroundings of the bubble as it rapidly imploded. A broad variety of outcomes can result from acoustic cavitation, including sonoluminescence, increased chemical activity in the solution due to the formation of primary and secondary radical reactions, and increase chemical activity through the formation of new, relatively stable chemical species that can diffuse further into the solution to create chemical effects (for example, the formation of hydrogen peroxide from the combination of two hydroxyl radicals formed following the dissociation of water vapor inside the collapsing bubbles what water is exposed to ultrasound.