Marangoni fireworks: Atomization dynamics of binary droplets on an oil pool

Abstract

Surface tension gradient due to concentration and temperature differences induces Marangoni forces. The Marangoni effect has been extensively studied to understand its fundamental underlying physics and its industrial applications. This paper describes the spreading and atomization dynamics of an aqueous 2-propanol (IPA) solution on sunflower oil. The spreading and self-atomization of droplets by the Marangoni effect with the evaporation of volatile components are herein observed. With 40 wt. % IPA solution droplets on sunflower oil, firework-like behavior was demonstrated with the Marangoni effect. To better understand the interplay between the evaporation and spreading/atomization characteristics, the temperature field on the oil pool was visualized and quantified using an infrared camera. The Marangoni flow driven by the temperature gradient near the spreading front was estimated and compared with the experimental spreading velocity. The experimental spreading velocity of the liquid film was found to roughly agree with the model prediction. By the atomization of the spreading IPA solution, thousands of atomized daughter droplets were counted, and the size distribution was determined. Additionally, fingering instability at the interface of the IPA solution and sunflower oil was quantitatively discussed, and the resulting wavelength on its interface was compared with the capillary model. We hope that our demonstration stimulates further studies that will yield deeper insights into the spreading and atomization dynamics of volatile binary droplets on a liquid pool.