Flexible Tri-switchable Wettability Surface for Versatile Droplet Manipulations

Smart surfaces with tunable wettability are promising due to their abilities to create diversified functionalities that the fixed surfaces cannot provide. However, limited by imprecise adjustment of structural geometry and almost conventional switching modes of wettability, it is still challenging to achieve the reversible switching between multiple wetting states. Herein, a novel tri-switchable wettability surface with an in situ switching ability is used for the manipulation of a given droplet, which consists of a stretchable substrate and a micron column array. The femtosecond laser direct writing technique is utilized to generate distinct wettability of the two components. Taking the advantage of good tensile properties, the surface morphology is adjusted in a rapid, reversible way to obtain diverse wetting performances from the lotus-like effect to rice-leaf-like anisotropy and then to the rose-petal-like effect. Based on the triplex wetting transition on the same surface, we further developed a multifunctional device to realize a range of in situ manipulations, including the surface self-cleaning, the directional transport of droplets, and the capture, the vertical transport, and release of droplets. This work paves the way for expanding the field of smart surfaces with tunable wettability beyond conventional dual-property wetting behavior and exhibits versatile manipulations of droplets for microfluidic applications.

具有可调节润湿性的智能表面前景广阔，因为它们能够创造出固定表面无法提供的多样化功能。然而，受限于结构几何形状的不精确调整以及几乎传统的润湿性切换模式，要实现多种润湿状态之间的可逆切换仍然颇具挑战。在此，一种具有原位切换能力的新型三态可切换润湿性表面被用于操控特定液滴，该表面由可拉伸基底和微米柱阵列组成。利用飞秒激光直写技术赋予这两种组件不同的润湿性。借助良好的拉伸性能，以快速、可逆的方式调整表面形貌，从而获得从类荷叶效应到类稻叶各向异性，再到类玫瑰花瓣效应的多样润湿性能。基于同一表面上的三重润湿转变，我们进一步开发了一种多功能装置，以实现一系列原位操控，包括表面自清洁、液滴的定向传输以及液滴的捕获、垂直传输和释放。这项工作为将具有可调节润湿性的智能表面领域从传统的双属性润湿行为拓展出去铺平了道路，并展示了用于微流体应用的液滴的多种操控方式。