EVAPORATION CHARACTERISTICS OF DROPLETS COATED WITH IMMISCIBLE LAYERS OF NONVOLATILE LIQUIDS

Evaporation rates of single glycerol core droplets coated with immiscible layers of dioctyl phthalate have been measured as a function of layer thickness. Experiments were conducted in an electrodynamic balance where a charged droplet was suspended in the path of a vertically polarized laser beam in a stream of dry air with precisely controlled temperature. Two light-scattering techniques based on angular and fixed angle scattered intensity data have been used to obtain the evaporation rate of the droplet. The intensities (i.e., resonant peaks) observed in the experimental scattering data at a fixed angle as a function of time have been interpreted by using elastic scattering theory to obtain the core droplet size and layer thickness with high precision. The experimental data show that the evaporation rate of a core droplet increases with increasing layer thickness. A theoretical model based on the diffusion of glycerol molecules through the dioctyl phthalate layer has been developed to interpret the experimental results. A parametric study based on the model is presented. The study shows that the liquid phase diffusion coefficient and the miscibility limit of glycerol in dioctyl phthalate greatly influence the evaporation rate of the core droplet.