Cleaning systems process mechanical energy

In the process of sonication, electrical energy is converted into mechanical energy. The sound waves produce cavitation (the process of formation and collapse of microscopic bubbles) which leads to great mechanical shear forces. Particles are hammered to form smaller particles, and the increased energy of the system can promote chemical reactions. Ultrasonic chemistry has recently been reviewed [34]. Most research in sonichemistry has been carried out in ultrasonic cleaning baths. Operations on scale can be carried out by using commercial flow cells [35],... 

Conditions can be deduced from the energy balance mentioned above under which the rewetting tension is positive, a precondition for the mechanism shown in Fig. 1.12. It should be said that re-wetting is the first step in the complex process of removal of hydrophobic layers from a solid. The oil droplets formed must also be sufficiently stabilised by the surfactant to prevent them coalescing. This takes place in many cleaning processes. When a water-insoluble substance is to be dispersed in water we can distinguish between thermodynamically stable and unstable dispersions. Thermodynamically unstable dispersions are the usual emulsions or dispersions of solids. Solubilisation systems and optically transparent emulsions, so-called micro-emulsions, are in a metastable state where drop growing by collision and coalescence cannot be completely suppressed. These systems are frequently called thermodynamically stable. 

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