Effect of non-ionic surfactants on transient cavitation in a megasonic field

High resolution chronoamperometry has been used to characterize the effect of two non-ionic surfactants, Triton® X-100 and NCW®-1002, on cavitation in aqueous solutions exposed to ~1 MHz sound field. Specifically, using ferricyanide as the electroactive species, temporal variation of current during its reduction on a 25 μm Pt microelectrode has been measured and is used to elucidate transient cavity behavior. The chronoamperograms for solutions exposed to megasonic field show current 'peaks' riding on the baseline current. These current 'peaks' have been attributed to the diffusion of ferricyanide species concentrated at the liquid-vapor interface of a transient cavity at the end of its collapse. In the presence of surfactants, the frequency of occurrence of current 'peaks' with magnitude ≥ 0.3 μA is found to increase indicating a higher number of transient cavity collapses. A simple mathematical model based on diffusion developed previously by the authors has been used to extract the maximum cavity size and range of distances between the center of the collapsing cavity and the electrode surface in the surfactant solutions.