Retradation of vapor-driven solutal Marangoni effect due to vapor absorption in the droplet*

Internal flow can be varied in an evaporating droplet due to changes in surface tension, driven by the Marangoni effect. Among various Marangoni effects, the solutal Marangoni effect is reported to be more significant than those driven by temperature and surfactants. In particular, vapor-driven solutal Marangoni flow, which avoids contamination, has been extensively studied for their potential in applications like mixing, coating, and droplet transport. However, most of previous research has focused on steady-state scenarios, considering only the adsorbed vapor on the droplet interface while overlooking vapor absorption in the droplet. In this talk, we present both experimental and numerical studies on the evolution of time-dependent internal flows and vapor mass flux across the droplet interface, considering vapor absorption. Our findings reveal that high absorption flux near the contact line induces a previously unreported transient inward-outward competing flow before the typical steady outward interfacial flow. This competing flow reduces flow magnitude in the early stages, and the duration of flow retardation is influenced by vapor source properties, such as solubility and vapor pressure, according to Henry's law. We propose that volatile liquids with lower solubility in water are more effective at generating vapor-driven solutal Marangoni flow compared to highly water-soluble liquids like ethanol and acetone, which have been typically used.