Abstract As a result of natural selection, cicadas can easily remove water droplets, pollen or dust from their wing surface. A gradient wetting state along the wing veins is revealed for the first time in this work. That is, the Wenzel state (hydrophilic) is transitioned to the Cassie-Baxter state (superhydrophobic) from foot to apex of the wing, which is attributed to different radius, height, and gap of the nanopillars on its surface. A fog harvesting test demonstrates that the cicada wing has a remarkable fog harvesting efficiency of 6.6 g m−2 s−1, which is comparable to the values reported for representative plant and animal surfaces. Superhydrophobic region exhibits a lower adhesion force to the droplets than hydrophilic region. So the accumulated droplets easily roll off from superhydrophobic to hydrophilic regions, and the light weight state on the wing can be maintained under its slight shaking. This work may direct the design of gradient wetting surfaces by mimicking the nanopillar structure on cicada wing and explore potential application in water harvesting.

中文翻译：

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纳米柱状蝉翼表面液滴运输的梯度润湿状态和有效的雾收集

摘要 由于自然选择，蝉可以很容易地去除翅膀表面的水滴、花粉或灰尘。在这项工作中首次揭示了沿机翼静脉的梯度润湿状态。也就是说，Wenzel 状态（亲水）从翼的脚部到顶点转变为 Cassie-Baxter 状态（超疏水），这归因于其表面纳米柱的不同半径、高度和间隙。雾收集测试表明蝉翼具有 6.6 g m-2 s-1 的显着雾收集效率，与代表性植物和动物表面报告的值相当。超疏水区域对液滴的粘附力低于亲水区域。所以累积的液滴很容易从超疏水区域滚落到亲水区域，在轻微晃动的情况下，仍能保持机翼上的轻量化状态。这项工作可以通过模仿蝉翼上的纳米柱结构来指导梯度润湿表面的设计，并探索在集水方面的潜在应用。