Buoyancy-Driven Motion of Bubbles in the Presence of Soluble Surfactants in a Newtonian Fluid

Abstract

We present our experimental results for the effect of bulk-soluble surfactants on the buoyancy-driven motion of an air bubble rising in square and rectangular channels filled with an immiscible liquid. Glycerol and glycerol–water solutions were chosen as the bulk fluid, and Triton X-100 and Aerosol-OT were used as surfactants. Bulk surfactant concentrations below as well as above the critical micelle concentration were considered. Even at very low bulk surfactant concentrations where the equilibrium surface tension did not change, bubbles rising through the surfactant solutions showed reduced mobility, especially for small bubbles. At larger surfactant concentrations, bubbles of all sizes showed lower terminal velocities. At a large enough bulk surfactant concentration, two peaks were seen in the velocity-volume curve. Increasing the bulk surfactant concentrations above the critical micelle concentration increased the mobility of the bubbles but still showed two peaks in the velocity-volume curve.