Gradient wettability is important for some living organisms. Herein, the dynamic responses of water droplets impacting on the surfaces of four regions along the wing vein of cicada Cryptotympana atrata fabricius are investigated. It is revealed that a gradient wetting behavior from hydrophilicity (the Wenzel state) to hydrophobicity and further to superhydrophobicity (the Cassie-Baxter state) appears from the foot to apex of the wing. Water droplets impacting on the hydrophilic region of the wing cannot rebound, whereas those impacting on the hydrophobic region can retract and completely rebound. The hydrophobic region exhibits robust water-repelling performance during the dynamic droplet impact. Moreover, a droplet sitting on the hydrophobic region can recover its spherical shape after squeezed to a water film as thin as 0.45 mm, and lossless droplet transportation can be achieved at the region. Based on the geometric parameters of the nanopillars at the hydrophilic and hydrophobic regions on the cicada wing, two wetting models are developed for elucidating the mechanism for the gradient wetting behavior. This work directs the design and fabrication of surfaces with gradient wetting behavior by mimicking the nanopillars on cicada wing surface.

中文翻译：

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沿着纳米柱蝉翼从温泽尔到鲁棒的卡西-巴克斯特态的梯度润湿转变及其潜在机理

梯度润湿性对某些生物很重要。这里，水滴沿的蝉的翅脉四个区域的表面上撞击的动态响应Cryptotympana蝉法氏囊被调查。揭示了从亲水性（Wenzel状态）到疏水性并且进一步到超疏水性（Cassie-Baxter状态）的梯度润湿行为从脚到机翼的顶点出现。撞击机翼亲水区域的水滴不能反弹，而撞击疏水区域的水滴可以缩回并完全反弹。疏水区在动态液滴撞击过程中表现出强大的拒水性能。而且，位于疏水区域上的液滴在被挤压成薄至0.45mm的水膜之后可以恢复其球形形状，并且可以在该区域实现无损的液滴输送。根据蝉翼上亲水和疏水区域的纳米柱的几何参数，开发了两种润湿模型来阐明梯度润湿行为的机理。通过模仿蝉翼表面上的纳米柱，这项工作指导了具有梯度润湿行为的表面的设计和制造。