| Abstract
| - It has previously been reported that the addition of low concentrations of ionic surfactants enhances thesteady-state sonoluminescence (SL) intensity relative to water (Ashokkumar; et al. J. Phys. Chem. B1997,101, 10845). In the current study, both sonoluminescence and passive cavitation detection (PCD) were usedto examine the acoustic cavitation field generated at different acoustic pulse lengths in the presence of ananionic surfactant, sodium dodecyl sulfate (SDS). A decrease in the SL intensity was observed in the presenceof low concentrations of SDS and short acoustic pulse lengths. Under these conditions, the inhibition ofbubble coalescence by SDS leads to a population of smaller bubbles, which dissolve during the pulse “offtime”. As the concentration of surfactant was increased at this pulse length, an increase in the acoustic cavitationactivity was observed. This increase is partly attributed to enhanced growth rate of the bubbles by rectifieddiffusion. Conversely, at long pulse lengths acoustic cavitation activity was enhanced at low SDS concentrationsas a larger number of the smaller bubbles could survive the pulse “off time”. The effect of reduced acousticshielding and an increase in the “active” bubble population due to electrostatic repulsion between bubbles arealso significant in this case. Finally, as the surfactant concentration was increased further, the effect ofelectrostatic induced impedance shielding or reclustering dominates, resulting in a decrease in the SL intensity.
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