Marangoni-driven spreading and receding of a volatile droplet on a liquid layer

When releasing a droplet onto a distinct nonmiscible liquid layer, for positive spreading parameter S, a surface tension driven spreading arises. Here, for positive S, we report the reverse after the initial spreading phase: a secondary receding of the deposited volatile droplet. This behavior is found to result from the competition between two opposite effects: solutal and thermal Marangoni stresses, with the latter built from droplet's evaporation. To clarify the effects of evaporation-induced Marangoni, accurate infrared thermography tests are performed. These tests reveal a maximal temperature gradient at the droplet edge near the recession time. Also, universal scaling laws are proposed for the spreading dynamic of a law-viscous insoluble drop onto a more viscous oil, with droplet volume variation resulting from the evaporation and typical receding time. These predictions are successfully compared with experiments.