The Wetting State of Water on a Rose Petal

摘要

The rose petal features surface structures that offer unique wetting properties. A water droplet placed on a rose petal forms a high contact angle but exhibits significant contact angle hysteresis, such that relatively large droplets remain stuck to the surface when it is tilted. Understanding this distinctive "parahydrophobic" wetting behavior can provide insight into the design of highly nonwetting, yet highly adhesive, synthetic surfaces. Surface features of the rose petal are characterized via focused ion beam scanning electron microscopy, which reveals microscale papillae that are partially covered with nanoscale striae. The wetting state of water on a rose petal is directly visualized using confocal microscopy. This experimental evidence confirms the microscale wetting behavior on the papillae, but cannot resolve the wetting behavior on the nanoscale striae. To infer the wetting state on the striae, an energy minimization-based model is developed and the results from the model are compared to the experimental evidence. In combination, the experimental findings and the model results reveal the wetting state of water on the hierarchical surface structure and explain the macroscopic wetting behavior of the rose petal.