Marangoni flowers when drop impacts on a miscible liquid film*

Interfacial flows driven by the Marangoni effect are common in daily life, such as tears of wine, coffee rings, and flow-patterns in soap bubbles. In this work, we investigate the various flower-like patterns which form when a water drop impacts a glycerol film at different speeds, where the Marangoni instability plays an essential role. Through high-speed imaging, we observed the formation of flowers is determined by surface tension instability at the air-liquid interfaces where present unsteady concentrations of glycerol and water after drop impact. Intense vortices inside the water layer are driven by the spatial variations of surface tension, which interacts with the evolution of glycerol-water concentration. At the same time, the impact patterns of drops at different speeds can tune the initial contact modes and therefore vary the final flower patterns.