Shear-Induced Lift Force on a Single Bubble in Surfactant Solutions

In this paper, single bubble motion in surfactant solutions is discussed. We focus on the change of the shear-induced lift force acting on a bubble when the bubble surface is contaminated by surfactant adsorption which leads the Marangoni effect. With the increase of Langmuir number corresponding to the decrease of desorption rate constant of surfactant, the lift force on a spherical bubble decreases from that on a clean bubble to near zero value. This reduction is related significantly to the asymmetry of pressure distribution on surface. Comparing the present result with our previous simulation using the stagnant cap model, the lift force of this study is larger than that of the stagnant cap model. This is because in a shear flow, the surface concentration distributes asymmetrically, and the asymmetry of the surface pressure produced by the shear appears stronger than that of the stagnant cap model.