The effects of a soluble surfactant on quadrupole shape oscillations and dissolution of air bubbles in water

Single air bubbles were ultrasonically trapped in aqueous solutions of the soluble surfactant Triton X-100. Quadrupole shape oscillations were induced by modulation of the radiation pressure and the free decay was recorded using an optical extinction technique. The frequency and damping were found to be maximal at a bulk surfactant concentration which only weakly affects the surface tension. At higher concentrations the frequency is reduced due to surface tension depression and the damping approaches a value several times that expected for a clean interface. These results are in qualitative agreement with theoretical predictions based on interfacial viscoelastic considerations. Bubble size and dissolution curves were obtained through the use of digitized bubble images. Dissolution rates are shown to be significantly enhanced by the presence of the surfactant.