Growth of Bubbles by Rectified Diffusion in Aqueous Surfactant Solutions

Abstract

Bubbles grow by the rectified diffusion process in an acoustic field. While there is a thorough understanding of this process for the air−water system, only limited experimental data is available in the literature for aqueous solutions containing surfactants. In order to expand the experimental database, we have determined the bubble growth rate by the rectified diffusion process in aqueous solutions containing sodium dodecyl sulfate (SDS) at various concentrations. Compared to water, the growth rate is higher in SDS solutions. The addition of 0.1 M sodium chloride to SDS results in a further enhanced growth rate at lower bulk concentrations of the surfactant. These results suggest that the surface loading of surfactant molecules plays a key role in enhancing the growth rate, likely due to an increase in the mass transfer resistance during the compression phase of the bubble oscillations. This is supported by results for the growth rates determined for dodecyl trimethylammonium chloride with the growth rate for a given equilibrium surface concentration higher than that of SDS. The experimentally determined bubble oscillation amplitudes for both surfactants decline relative to that of water, consistent with previously published models.