Buoyancy-driven motion of bubbles in the presence of soluble surfactants

Abstract

We present our experimental results for the effect of bulk-soluble surfactants on the buoyancy-driven motion of an air bubble rising in circular, square and rectangular channels filled with a liquid. The bulk fluid is either Newtonian or viscoelastic with or without surfactants. In a Newtonian fluid, small bubbles are nearly spherical travelling with a velocity much lower than the Hadamard-Rybczinski velocity. Long bubbles were prolate translating with a velocity independent of the bubble size. Cusps form in all the viscoelastic systems studied. Even in the presence of small amounts of surfactants bubble shapes were elongated and mobility is reduced due to Marangoni effects. At surfactant concentrations above CMC small bubbles are partially remobilized while long bubbles are completely remobilized. The effect of the channel geometry on bubble mobility and deformation are also presented