Exploring fluorescence lifetime potential for analyzing the composition of vaporizing bicomponent droplets

Predicting droplet evaporation is particularly complex when the liquid phase consists of multiple components. To date, only a limited number of physical optical phenomena have been used to non-intrusively measure the composition of droplets. Laser-induced fluorescence is a promising approach, as the emission and absorption of certain fluorescent dyes are known to depend on solvent polarity, viscosity, and, more generally, the chemical environment. However, a challenge is that fluorescence signal intensity is generally sensitive to both temperature and composition. This study investigates fluorescence lifetime measurements as a robust alternative. We demonstrate that, with a well-chosen fluorescent dye, it is possible to measure the composition of bicomponent droplets using a single dye and a single detection band, with minimal constraint on detection band selection, and without ambiguity due to temperature variations. To validate the technique, it is applied to acoustically levitated droplets across several mixtures that exhibit markedly different behaviors.