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Micro–Nano Hierarchical Structure Enhanced Strong Wet Friction Surface Inspired by Tree Frogs
Advanced Science ( IF 15.1 ) Pub Date : 2020-08-09 , DOI: 10.1002/advs.202001125
Liwen Zhang 1 , Huawei Chen 1, 2 , Yurun Guo 1 , Yan Wang 1 , Yonggang Jiang 1 , Deyuan Zhang 1 , Liran Ma 3 , Jianbin Luo 3 , Lei Jiang 4
Affiliation  

Superior wet attachment and friction performance without the need of special external or preloaded normal force, similar to the tree frog's toe pad, is highly essential for biomedical engineering, wearable flexible electronics, etc. Although various pillar surfaces are proposed to enhance wet adhesion or friction, their mechanisms remain on micropillar arrays to extrude interfacial liquid via an external force. Here, two‐level micropillar arrays with nanocavities on top are discovered on the toe pads of a tree frog, and they exhibit strong boundary friction ≈20 times higher than dry and wet friction without the need of a special external or preloaded normal force. Microscale in situ observations show that the specific micro–nano hierarchical pillars in turn trigger three‐level liquid adjusting phenomena, including two‐level liquid self‐splitting and liquid self‐sucking effects. Under these effects, uniform nanometer‐thick liquid bridges form spontaneously on all pillars to generate strong boundary friction, which can be ≈2 times higher than for single‐level pillar surfaces and ≈3.5 times higher than for smooth surfaces. Finally, theoretical models of boundary friction in terms of self‐splitting and self‐sucking are built to reveal the importance of liquid behavior induced by micro–nano hierarchical structure.

中文翻译:

受树蛙启发的微纳米分层结构增强强湿摩擦表面

优异的湿附着和摩擦性能,无需特殊的外部或预加载法向力,类似于树蛙的脚趾垫,对于生物医学工程、可穿戴柔性电子产品等非常重要。尽管提出了各种柱表面来增强湿附着或摩擦,它们的机制保留在微柱阵列上,通过外力挤出界面液体。在这里,在树蛙的脚趾垫上发现了顶部具有纳米腔的两级微柱阵列,它们表现出比干摩擦和湿摩擦高约 20 倍的强边界摩擦力,而不需要特殊的外部或预加载法向力。微观尺度的原位观察表明,特定的微纳分级柱反过来触发三级液体调节现象,包括两级液体自分裂和液体自吸效应。在这些效应下,所有柱子上自发形成均匀的纳米厚液桥,产生强烈的边界摩擦,其比单层柱子表面高约 2 倍,比光滑表面高约 3.5 倍。最后,建立了自分裂和自吸方面的边界摩擦理论模型,以揭示微纳米分级结构引起的液体行为的重要性。
更新日期:2020-08-09
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