Journal of Bionic Engineering (2023) 20:2774–2785https://doi.org/10.1007/s42235-023-00406-1

Superhydrophobic Purple Orchid Leaves: Variation in Surface Morphology During the Vegetation Stages Leading to Diversity in Wettability 

Longsheng Lu1  · Guoxiang Jiang1  · Kaikai Li1  · Yingxi Xie1  · Jiao Gao2

Jiao Gao gaojiao@scut.edu.cn 

1 School of Mechanical & Automotive Engineering, South China University of Technology, Guangzhou 510641, China 

2 Shien-Ming Wu School of Intelligent Engineering, South China University of Technology, Guangzhou 511442, China

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 diferent 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 diference 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 artifcial leaves, the nano-waxy layer is proved to be more efective than that of the micro-bumps on the surface wettability. The results of study are of a great signifcance for guiding the design and fabrication of plant-inspired bionic superhydrophobic surface. 

Keywords: Superhydrophobicity · Surface morphology · Micro-nano hierarchical structure · Purple orchid leaf · Bionic