Ultrasonic horn acoustic cavitation

Fig. 2.7 Acoustic cavitation-induced polymerisation of a monomer to generate polymer latex particles using 20 kHz ultrasonic horn [61]. The shear forces generates emulsion droplets. Radicals generated within cavitation bubbles react with monomer molecules to generate monomer radicals that diffuse into monomer droplets to initiate polymerisation process...

McLean and Mortimer [187] have studied the variations in HO free radical production during the sonication of aqueous solutions at different powers at 970 kHz. A typical curve is given in Figure 36. From this it is clear that a threshold exists for radical production, after which there is a linear correlation with acoustic power up to a limiting value which probably corresponds with surface cavitation . Acoustic power was calibrated with a radiation balance and a PVDF hydrophone. Repeatability on experiments performed on the same day was less than 15%, but day-to-day variations could be as much as 50%, probably mainly due to small uncontrolled changes in the alignment of the reaction chamber (a test tube dipped in a water tank) with the ultrasonic source which was an acoustic horn. 

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