Abstract
Droplet evaporation is one of the most commonly observed phenomena and plays an important role in many applications such as in spray cooling, coating, and inkjet printing. Mechanisms such as dynamics of the contact line, evaporation-induced phase transitions, and formation of patterns on the substrate interact with each other in the evaporation of droplets. In this study, we investigated the effect of surface mixed wettability on water sessile droplet evaporation. The transient contact angle, center-height, contact radius, surface area, and droplet volume were experimentally measured and numerically estimated. Surfaces with mixed wettability consisting of hydrophilic islands surrounded by less hydrophilic area were fabricated. Visualization was conducted to capture droplet dynamics during evaporation using two high-speed cameras. According to the obtained results, there were three distinct stages in the water evaporation process: a constant contact radius mode, a constant contact angle mode, and a mixed-mode. The COMSOL 5.4 software was used for numerical analysis. According to the results, the receding contact angle and Marangoni instability in the droplet are two main factors that alter droplet dynamics and droplet evaporation.
