Evaporation Dynamics of Deionized Water Droplets on Hydrophobic Leaves

Self-cleaning applications based on bionic surface designs requires an in-depth understanding of unique and complex wetting and evaporation processes of sessile droplets on natural biosurfaces. To this end, hydrophobic bamboo and Kalanchoe blossfeldiana leaves are excellent candidates for self-cleaning applications, but various properties, such as the heat and mass transfer processes during evaporation, remain unknown. Here, the dynamics of contact angle, radius, and heat and mass transfer during evaporation of sessile droplets on bamboo and Kalanchoe blossfeldiana leaves with roughness in the range 2.8-3.4 μm are thoroughly investigated. In particular, the "stick-jump" phenomenon is observed on bamboo leaves, which was further analyzed in terms of Gibbs free energy and indicates that a larger roughness would also render more likely the jump of the drops. Moreover, by means of the Wenzel wetting model, the functional relation between the rough structure parameters of the bamboo leaf surface and the system intrinsic energy barrier was established, and the evaporation kinetics of droplets was elucidated. We anticipate that this study offers a framework for understanding the behavior of droplets on the surface of hydrophobic biomimetic materials, which may lead to the rational design of self-cleaning bionic-type surfaces.