High-speed observation of bubble dynamics influenced by surfactant molecules

Abstract

Surfactant molecules affect the dynamics of acoustic bubbles such as the oscillation of expansion and contraction and a bubble coalescence when adsorbed with bubble/liquid interface. A high-speed shadowgraph of acoustic bubbles was observed in surfactant SDS solutions using a high-speed camera with a speed of a million fps. The experimental results of time evolution of bubble diameter showed that a surfactant-adorbed bubble favors a spherical oscillation. Histograms of maximum bubble diameters obtained at several frequencies indicated that the number of large-size bubble considerably decreased compared to the case of pure water and this tendency was marked at higher frequencies. The histograms measured at various SDS concentrations at 87 kHz showed that the decrease in the number is significant at 5 mM. The results are elucidated in terms of electrostatic repulsion between charged bubbles, which inhibits the bubble coalescence.