Abstract: Learning hydrophobic phenomena from nature is always a promising approach to design the superhydrophobic surface. Purple orchid leaf which processes superhydrophobicity is an ideal plant model, and through mimicking its structure, the surface with excellent hydrophobicity is able to be obtained. However, the unclear of the diversity in wettability during the different vegetation stages and the absence of its relation to the surface morphology limits the further enhancement of the inspired structure. Here, we analyze the wettability difference as the leaf grows from tender to mature and then to senescent. Combining with the variation of surface morphology and chemical composition, the well-developed micro-scale basic unit bumps with dense nano-scale waxy layer on the surface are proven to be responsible for the best hydrophobicity of the mature leaf. The presence of the undeveloped or damaged micro-nano hierarchical structure reduces the formation of air pockets at the interface, leading to the decrease of the wettability for leaves at other stages. Moreover, by fabricating artificial leaves, the nano-waxy layer is proved to be more effective than that of the micro-bumps on the surface wettability. The results of study are of a great significance for guiding the design and fabrication of plant-inspired bionic superhydrophobic surface.

Key words: Superhydrophobicity , · Surface morphology , · Micro-nano hierarchical structure , · Purple orchid leaf , · Bionic