Surfactant Sorption on a Single Air Bubble in an Ultrasonic Standing Acoustic Wave Field

Ultrasound application presents a promising non-intrusive way to enhance and facilitate
mass transfer in aqueous systems. This enhanced mass transfer can influence
the sorption processes in multiphase flows. Previous studies investigating the
impact of ultrasound on sorption, have reported an increase in either desorption
due to the rise in liquid temperature or adsorption due to the additional convective
mass transfer resulting from acoustic streaming. In this study, low intensity
ultrasound with a frequency of 36 kHz was deployed to evaluate the sorption process
of Triton X-100 on the surface of a single bubble, placed along the standing
acoustic wave using profile analysis tensiometry. Furthermore, microscopic particle
image velocimetry was used to understand the role acoustic streaming might
play during different stages of the sorption process. Contrary to expectations, the
results showed no considerable change in surface tension and sorption dynamics
after sonicating both fresh and surfactant-loaded bubbles. The results of this study
suggest that the observations from previous studies may be attributed to the additional
energy input of the acoustic wave into the system rather than the presence
of an external acoustic field.