Vaporization of acoustically levitated alcohol/water droplets in humid air

Abstract

The evaporation of droplets composed of water and light alcohols (ethanol, 2-propanol, and 1-propanol) is investigated using acoustically levitated droplets, combined with simultaneous measurements of droplet size and chemical composition. Droplet evolution is influenced by the relative volatility of the components, ambient humidity, and temperature. Ethanol and 2-propanol droplets consistently evolve toward pure water due to rapid alcohol evaporation and condensation of water from the surrounding air. In contrast, 1-propanol droplets can either lose most of their alcohol or retain a significant fraction, depending on the initial composition and environmental conditions. The combined experiments and modeling reveal the existence of stable final compositions under given conditions, toward which droplets naturally evolve, forming what can be described as a “composition attractor.” This attractor arises from the balance between evaporation, water absorption, and non-ideal mixture effects. Similar behavior may occur for other liquid mixtures with moderate differences in volatility. These findings provide new insight into the complex dynamics of multicomponent droplet evaporation and highlight the role of environmental conditions in determining the final composition.