Fluorescent Marangoni Flows under Quasi-Steady Conditions.

Marangoni flow is among the most intriguing effects in complex fluids and interfacial science. We report here on a fluorescent surfactant that enables to monitor Marangoni flows under quasi-steady conditions, without the need of invasive tracers. The Marangoni zone is clearly visible, and its dynamics can be quantitatively probed both at the air-water interface and within the bulk. In particular, we show that the Marangoni zone exhibits unexpected dependencies with the container size and water depth with the pyrene-tailed surfactant. Additionally, recirculation flows are evidenced by fluorescence near the bottom of the container. This fluorescent probe may find other useful applications in deciphering the complexity of the ubiquitous Marangoni effect.