Nature's Design of Hierarchical Superhydrophobic Surfaces of a Water Strider for Low Adhesion and Low-Energy Dissipation
Nature's Design of Hierarchical Superhydrophobic Surfaces of a Water Strider for Low Adhesion and Low-Energy Dissipation
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DOI：
10.1021/la103442b
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发表时间：
2010-12-21
期刊：
影响因子：
3.9
通讯作者：
Hwang, Keh-chih
中科院分区：
文献类型：
--
作者：
Su, Yewang;Ji, Baohua;Hwang, Keh-chih
研究了水腿与水面的湿粘附机理。首先，我们表明，纳米级到微米级的层次表面结构的漫游者的腿是至关重要的稳定防水性能的腿。最小结构是为了即使在恶劣的环境条件下也能保持稳定的Cassie状态而制成的，这为最小结构的尺寸设定了上限。由于不对称的表面张力，接触线处的表面结构的最大应力和最大变形取决于尺寸，这为最小结构的尺寸设定了下限。表面层次结构可以通过稳定Cassie状态，增加表观接触角，减少接触面积和接触线长度，大大减少水与腿之间的粘附。其次，建立了水下机器人的二维模型，分析了水下机器人腿在水面上的受力和离水过程。我们发现，腿的表面的超疏水性是至关重要的，以减少分离力和分离能量。最后分析了仿水机动过程中腿击水面的动力学过程。我们发现，腿的大长度，不仅减少了能量耗散在准静态的压力和拉动过程中，但也提高了能量转换的效率，从生物能到动能的动态过程中操纵的水？本研究所发现之机械原理，可为设计上级防水表面及新颖之水中机器人提供有用之指导。
The mechanics of wet adhesion between a water strider's legs and a water surface was studied. First, we showed that the nanoscale to microscale hierarchical surface structure on striders' legs is crucial to the stable water-repellent properties of the legs. The smallest structure is made for the sake of a stable Cassie state even under harsh environment conditions, which sets an upper limit for the dimension of the smallest structure. The maximum stress and the maximum deformation of the surface structures at the contact line are size-dependent because of the asymmetric surface tension, which sets a lower limit for the dimension of the smallest structure. The surface hierarchy can largely reduce the adhesion between the water and the legs by stabilizing the Cassie state, increasing the apparent contact angle, and reducing the contact area and the length of the contact line. Second, the processes of the legs pressing on and detaching from the water surface were analyzed with a 2D model. We found that the superhydrophobicity of the legs' surface is critically important to reducing the detaching force and detaching energy. Finally, the dynamic process of the legs striking the water surface, mimicking the maneuvering of water striders, was analyzed. We found that the large length of the legs not only reduces the energy dissipation in the quasi-static pressing and pulling processes but also enhances the efficiency of energy transfer from bioenergy to kinetic energy in the dynamic process during the maneuvering of the water striders. The mechanical principles found in this study may provide useful guidelines for the design of superior water-repellent surfaces and novel aquatic robots.