The effect of surface-active agents on two-phase flows will be studied. Flow types “air bubbles in the liquid” and “liquid drops in another immiscible liquid” will be focused. Some specific situations, in which the surfactants modify the flow at the bubble/drop scale and in which this modification cannot be explained by a simple change of the equilibrium surface tension, will be investigated experimentally. These situations are (i) the shape oscillations of a bubble/drop, either freely-rising or attached at a capillary tip; focus is put on the modification of oscillation frequency and decay time by surfactants; (ii) the coalescence of bubbles/drops, and also their attachment to a solid surface, with a focus on the drainage of liquid film between them; (iii) the bubble-solid surface collision, with a focus on suppression
of the bubble rebound caused by surfactants and also on the modification of the attachment time. The research should enlighten and document the effect of interfacial properties other than surface tension on two-phase flows.