Quantifying the interacting mechanisms in shape evolution of sessile volatile droplets

Abstract

Non-uniform distribution of interfacial mass flux across an evaporating droplet will subsequently induce a temperature gradient across the liquid-air interface, and result in thermal Marangoni stress that reforms the flow field inside the droplet. Recent study (Shiri, et al. Phys. Rev. Lett. 2021, Yang, et al. Langmuir 2022) confirmed the role of thermal Marangoni effect on the shape of evaporating single component droplets on completely wetting substrates. Nevertheless, a comprehensive evaluation of the interacting mechanisms is still lacking due to the intrinsic limitation of experimental techniques to decompose the different influence factors. To this end, we formulate a mathematical model to simulate the evaporation of volatile droplets on completely wetting substrates based on the lubrication theory. With this model, we elucidate the interacting physical mechanisms that governs the droplet kinetics during phase change, which includes the capillary effect, the thermal Marangoni effect, the interface motion due to evaporation, as well as the removal of energy barriers by precursor film. A phase diagram is summarized in terms of the Knudsen number and liquid-to-solid Biot number, which quantifies the prevalence of the interacting effects.