Dynamic droplet morphology measurement method based on digital image correlation and refraction effect

The measurement and analysis of the droplet morphology on a solid surface play a crucial role in investigating solid–liquid interactions and characterizing the properties of surfaces. The contact angle is a widely used parameter in characterizing the droplet, but it cannot well describe the irregular shapes, which can be easily found in the investigations of the spreading and evaporation of the droplet. In this study, a novel method for three-dimensional measurement of the transparent droplet morphology is developed by combining droplet-induced image displacement with the principles of refraction imaging. First, a full-field optical method is employed to measure the image displacement of the solid surface caused by the refraction of the droplet. Second, a physical model is established based on refraction imaging, so the relationship between image displacement and the morphology of the droplet is formulated. Finally, the three-dimensional surface of the droplet is reconstructed by resolving the physical formulations. Experimental results demonstrate that the proposed method can accurately measure the three-dimensional morphology of droplets on solid surfaces and is applicable for irregular liquid surfaces. This method provides important technical support for studying droplet spreading, evaporation, and other related behaviors.