Differential pulse and chronoamperometric studies of insonated systems: Acoustic streaming and cavitational effects

Chronoamperometry has been undertaken at insonated electrodes of both micro and macro dimensions, for a range of simple, well-defined redox couples in water (298 K), DMF (298 and 218 K), and ammonia (218 K) as solvents. These are analyzed to assess the relative contributions of acoustic streaming and cavitational: activity to the observed currents: both contribute significantly under the usual conditions adopted for sonovoltammetry. Differential pulse voltammetry (DPV) was then used to explore the nature of the diffusion layer prevailing under steady-state electrolysis of insonated macroelectrodes. Simulations showed that pure convection within a diffusion layer enhances the DPV currents for simple redox systems as compared to silent conditions. The experimentally observed decrease was attributed to cavitational disruption of the diffusion layer leading to a physical model of an insonated electrode which may be described as a steady diffusion layer a few microns thick brought about by acoustic streaming which is occasionally and randomly punctuated by a cavitational event. The frequency and violence of the event is dependent on the solvent and ultrasound power, except at very short electrode-to-horn separation where the cavitational contribution becomes substantial.