Adsorption of Surfactants at the Gas/Solution Interface of Cavitation Bubbles:  An Ultrasound Intensity-Independent Frequency Effect in Sonochemistry

Abstract

A major limitation in determining the effects of ultrasound frequency in sonochemistry in relation to cavitation is that no reliable relationship exists between the energy supplied to the system and the energy converted by the cavitation process in producing a sonochemical effect. However, the current study presents a frequency effect that is independent of the energy supplied to the system. Spin-trapping of secondary carbon radicals with 3,5-dibromo-4-nitrosobenzenesulfonic acid-d 2 (DBNBS-d 2 ) and electron paramagnetic resonance (EPR) have been used to determine the relative ability of two nonvolatile surfactants [sodium 1-pentanesulfonic acid (SPSo) and sodium dodecyl sulfate (SDS)] to scavenge • H atoms and • OH radicals at the gas/solution interface of cavitation bubbles. The results obtained at 354 and 1057 kHz are compared to those observed previously at 47 kHz (Sostaric, J. Z.; Riesz, P. J. Am. Chem. Soc. 2001, 123, 11010-11019). At particular bulk surfactant concentrations, both surfactants reached a limiting plateau value in radical scavenging ability. At 354 kHz (and 47 kHz), the magnitude of this plateau was greater for SPSo compared to that for SDS. However, at 1057 kHz, no difference in the plateau value was observed between SPSo and SDS. Decreasing the ultrasound intensity at constant frequency during the sonolysis of SPSo and SDS resulted in a decrease in the -• CH-radical yield. However, there was no change in the relative plateau yield of -• CH-radicals between SPSo and SDS. Thus, at plateau concentrations, the relative ability of these n-alkyl chain surfactants to scavenge radicals at the gas/solution interface of cavitation bubbles depends on the frequency of sonolysis but is independent of ultrasound intensity. The results were interpreted in terms of a decrease in the rate of change of the surface area of "high-energy-stable cavitation bubbles" at higher frequencies. This would affect the relative adsorption and hence radical scavenging efficiencies of SPSo and SDS at the gas/solution interface of these types of cavitation bubbles.

Influence of experimental parameters on sonochemistry dosimetries: KI oxidation, Fricke reaction and H2O2 production

“…Sostaric and Riesz [26] indicated that the Fe 3+ yield at 354 kHz for 3 min under argon gas increased with an increase in power up to a plateau (50-60 W).…”

The novel synthetic route of 3,5-dimethyl-1-(3-phenylpropyl)-1H-pyrazole under solid–liquid phase transfer catalysis conditions assisted by an ultrasound application—A study of some kinetic parameters

“…There was no possibility for the direct interaction between ultrasound and substance, and in such a way it is an indirect phenomenon, so that cavitation must be facilitated to encourage a chemical reaction. Hence, the make use of ultrasound to enhance chemical reactivity [24,25] is now familiar as a feasible environmental safe alternative machinery. Kinetics of the reaction in synthesizing 3,5-dimethyl-1-(3-phenylpropyl)-1H-pyrazole, such as agitation speed, amount of catalyst, quaternary ammonium salts, amount of sodium hydroxide and temperature on the conversion were investigated in detail.…”

Effects of initial concentration of LASs on the rates of sonochemical degradation and cavitation efficiency

“…While the sonolysis of surfactant has been extensively examined [9][10][11][12][13][14][15][16][17][18], the behavior of surfactants during acoustic cavitation is still unclear. For example, Yang et al [10].…”

“…reported the sonochemical degradation of the surfactants, alkyl acids and alkyl amines, where they discussed mainly the effects of the alkyl chain length of the solute and the pH of the solution on the intensity of sonoluminescence. In addition, the spin-trapping studies by Sostaric and Riesz [16,17] showed that anion surfactants with shorter alkyl chain length were more efficiently accumulated at the cavitation bubble interface under continuous sonication. Based on previous reports [10,16,17], it is suggested that the degradation rates of anion surfactants are affected by their alkyl chain length.…”

“…In addition, the spin-trapping studies by Sostaric and Riesz [16,17] showed that anion surfactants with shorter alkyl chain length were more efficiently accumulated at the cavitation bubble interface under continuous sonication. Based on previous reports [10,16,17], it is suggested that the degradation rates of anion surfactants are affected by their alkyl chain length. Although a number of previous studies on the sonolysis of LASs have been reported, there is no systematical discussion about the relation between the initial bulk concentrations and the rates of sonochemical degradation.…”