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The mechanisms of the sonochemical decomposition of n-alkyl surfactants, which has varying alkyl lengths, and the general applicability of GAMMA(sub eq) to predict the ability of different classes of surfactants to absorb at the gas/solution interface of bubbles in an ultrasonic field are evaluated by using EPR and spin-trapping studies. The results show that the decomposition off surfactants depends on their chemical structure and their ability to equilibrate between the bulk solution and the gas/solution interface of cavitation bubbles.

A quantitative relationship between ultrasound frequency and chemical yields during sonolysis of aqueous surfactant solutions is described. The studied have shown that C[H.sub.SBSo]/C[H.sub.SDS] is independent of ultrasound intensity and geometry of various exposure systems.

The effect of ultrasound frequency on the pulsed sonolytic degradation of octyl benzenesulfonate (OBS) is examined. The studies have shown that sonolytic degradation of OBS has depended on both the sonochemical activity and the accumulation of OBS on cavitation bubble surfaces.

A solution of perchlorotriphenylmethyl triester (PTM-TE, a stable organic free radical) dissolved in hexamethyldisiloxane (HMDS) is encapsulated by using high-power ultrasound into a polymerized shell of bovine serum albumin (BSA). It is found that the method leads to an overall loss of EPR signal intensity from the washed suspension of microspheres and the encapsulated PTM-TE/HMDS solution is found to be sensitive to the partial pressure of oxygen in the muscle and tumor tissue of mice.

An ultrasound-independent frequency effect was observed, which was made possible by carefully choosing the 'reference' and 'test' sonochemical reactions. It is concluded that sodium 1-pentaanesulfonic acid (SPSo) and sodium dodecyl sulfate (SDS) to accumulate at the gas/solution interface of cavitation bubbles.

It has been shown that pulsed ultrasound can influence the amount of surfactant that can adsorb to and decompose at the surface of cavitation bubbles. However, the effect of ultrasound frequency on this process has not been considered. The current study investigates the effect of ultrasound frequency on the pulsed sonolytic degradation of octyl benzenesulfonate (OBS). Furthermore, the effect of pulsing and ultrasound frequency on the rate of *OH radical formation was determined. OBS degradation rates were compared to the rates of *OH radical formation. In this way, conclusions were made regarding the relative importance of accumulation of OBS at cavitation bubble surfaces versus sonochemical activity to the sonochemical decomposition of OBS under different conditions of sonolysis. Comparisons of the data in this way indicate that sonolytic degradation of OBS depends on both the sonochemical activity (i.e., *OH yield) and the accumulation of OBS on cavitation bubble surfaces. However, under a certain set of pulsing and ultrasound frequency exposure conditions, enhanced accumulation of OBS at the gas/solution interface of cavitation bubbles is the sole mechanism of enhanced degradation due to pulsing. On the basis of this finding, conclusions on how pulsing at various ultrasound frequencies affects cavitation bubbles were made.