Instability of Marangoni flow in the presence of an insoluble surfactant. Experiments

The stability and structure of solutocapillary Marangoni flow initiated by a localized concentration source in the presence of an adsorbed layer of insoluble surfactant is investigated experimentally. It has been established that the main axisymmetric flow becomes unstable with respect to azimuthally periodic disturbances which leads to the appearance of the surface flow with a multi-vortex structure. The structure of the secondary flow is investigated depending on the intensity of the main flow and on the surface density of the surfactant. It has been shown that the azimuthal wave number increases with the growth of the Marangoni number and decreases with the surface density of the surfactant. A threshold value of the surface density of the surfactant, at which the Marangoni flow does not occur, has been defined.