1997年,德国波恩大学植物学家Wilhelm Barthlott教授发现,当水滴滴在荷叶表面上,水滴在荷叶表面变成了滚动的水珠,带走荷叶表面的尘土等污染介质,使表面始终保持一尘不染的状态。这就是“荷叶效应”。研究发现,荷叶表面大量微米级乳突结构及纳米级低表面能蜡质晶体共同构成微纳分级结构。而足够的粗糙度与低表面能化学成分的协同作用使荷叶具有高接触角与低滚动角,呈现出超疏水自清洁状态。目前,在建筑、纺织、航空、通讯等领域均已得到应用。
“莲出淤泥而不染”。荷叶是睡莲科多年生具根茎的水生植物,喜温暖、喜水,叶类圆盾形,全缘或稍成波状,浮于水面之上,表面不易残留污染物。SEM图像显示,荷叶表面覆盖着许多直径为5-9μm的乳突结构,而且,微米级乳突结构上又覆盖着平均直径为124.3 ± 3.2 nm的纳米结构分支,构成微纳分级结构。“荷叶效应”为仿生润湿性功能表面与结构设计提供了极佳的参照。
荷叶表面微米级乳突与纳米级蜡质晶体结构间的凹槽处捕获空气,从而形成“空气垫”,产生负压,使得水滴在与表面接触过程中并未完全浸入表面的粗糙结构,具有较高的水接触角及极小的滚动角,有效阻止荷叶表面被水润湿,呈现出优异的超疏水性能及自清洁效应。
图1(a)荷叶光学图像;(b)表面微观形貌(SEM图像);(c)表面水滴滚动状态;(d)润湿机制图(Cassie模型)。
仿照荷叶效应,所制备出的仿生超疏水表面呈现出自洁、防污、防冰、减阻、防腐等特性,在建筑、纺织、航空、通讯等领域都具有十分广阔的应用及发展前景。
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Wilhelm Barthlott
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