The effect of soluble anionic surfactants on rise velocity and mass transfer at single droplets in systems with Marangoni instabilities

The toluene/acetone/water system without surfactants shows strong Marangoni instabilities with distinct fluid dynamics and enhanced mass transfer. The present study investigates the impact of an anionic surfactant (SDS) on rise velocity and mass transfer both in the spherical and the oscillating droplet regime in time resolved measurements. Results are compared with the respective pure system and with correlations from literature. Velocity measurements reveal that the smaller the droplets are the lower is the surfactant concentration where the terminal velocity of the corresponding rigid sphere is attained. Mass transfer measurements show that mass transfer is still significantly enhanced by Marangoni convection although the surfactant concentration was believed to be high enough to hinder interfacial movement.