Photothermally Caused Propylene Glycol–Water Binary Droplet Evaporation on a Hydrophobic Surface

Photothermal effect has shown great promise in manipulating the droplet evaporation. In this work, the evaporation of a propylene glycol–water binary droplet on the hydrophobic surface induced by the photothermal effect of a focused infrared laser with a wavelength of 1550 nm was experimentally investigated. Dynamic evaporation behaviors were discussed through the visualization method and image processing technique. Experimental results showed that the photothermally induced evaporation of such a binary droplet could be divided into two stages: the first stage dominated by the evaporation of water with more volatility represented by rapid variations of the droplet volume and geometric parameters and the second stage dominated by the evaporation of propylene glycol with less volatility represented by a smaller slope. Correspondingly, the binary droplet evaporation first experienced the mixed mode greatly related to the more volatile component, and then the constant contact radius mode greatly related to the less volatile component. In addition, the effects of the initial composition and input laser power were also discussed. This work provides a deep understanding of the photothermal effect of a focused light-caused evaporation behaviors of the propylene glycol–water binary droplets and a potential route to accommodate various applications using the evaporation of the binary droplet.