Measurement of the surface concentration (liquid) of an evaporating multicomponent droplet using pendant droplet method

The surface concentration on the liquid side of the interface of an evaporating multicomponent droplet could be different from the bulk concentration. In this work, surface tension is used as a means to measure surface concentration of an evaporating multicomponent droplet. Surface tension is measured using pendant droplet method that relies on the best fit between theoretical and experimental drop profiles. Surface tension is a surface property, and it exhibits a dependence on concentration. Hence, it is an ideal candidate to track the variation of surface concentration during the evaporation of a multicomponent droplet. This method is used to study the evaporation of ethanol–water and methanol–water droplets. The correctness and applicability of this technique are critically assessed, and important observations are made for single droplet evaporation for these binary mixtures.