八宝景天叶片表面润湿性测试与疏水机理分析

为探寻用于超疏水表面制备的仿生原型,测试了八宝景天(Hylotelephium erythrostictum)叶片表面对水滴的润湿性,采用扫描电镜和三维形貌干涉仪对叶片表面微形貌结构进行观测并提取特征参数,基于Wenzel方程和Cassie-Baxter方程构建模型用以分析叶片表面的疏水机理。结果表明:润湿性随叶片类型的不同而呈现差异,其中新鲜幼叶正、反表面的接触角分别为(147.25±3.79)°和(137.46±4.03)°,新鲜幼叶反面的接触角高达152.54°;叶片表面由排列连续致密且呈椭球形的凸包和交错排列成网状且形貌不规则但可辨别轮廓的蜡质晶体构成,不同类型叶片表面的凸包形貌呈现显著差异但蜡质晶体形貌未有明显区别;幼叶正、反表面的凸包具有相似的高度但分布密度和投影面积显著不同,蜡质晶体层的高度和面积比未有明显差异;微米级凸包和纳米级蜡质晶体的协同作用使叶片表面呈现疏水特性且蜡质晶体发挥关键作用。基于Cassie-Baxter方程构建的模型能够有效揭示叶片表面的疏水机理,并可为超疏水表面的仿生制备提供理论支持。

Wettability measurement and hydrophobicity mechanism analysis of leaf surface of Hylotelephium erythrostictum

To search a bionic prototype for fabrication of superhydrophobic surfaces, the wettability of water droplets on leaf surfaces of Hylotelephium erythrostictum is measured, and the micromorphology of these leaf surfaces is examined by scanning electron microscope and three-dimensional shape, and the characteristic parameter is extracted. Based on the Wenzel equation and Cassie-Baxter equation, theoretical models are proposed to analyze the leaf surface''s hydrophobicity mechanism. Results present that the contact angles change remarkably with the variation of leaf types, the contact angle of water droplets on up side and low side of the fresh young leaf are recorded as (147.25 ± 3.79)° and (137.46 ± 4.03)°, and the greatest value is recorded as 152.54° when the water droplet contact with fresh young leaf''s low side, demonstrating the fresh young leaf possesses superhydrophobic property. The leaf''s surface morphology consists of convex halls and wax coverings, the ellipsoidal convex halls from young leaf show a continuous and dense arrangement with the similar height, the significant different distribution density and projected area. The wax coverings emerge as discernible platelet-formed wax crystals with an irregular pattern and overlap each other to generate numerous cavities, and the wax crystal''s geometrical parameters from both sides of the young leaf exhibit extremely similar values. Both the micro-scaled convex halls and the nano-scaled wax crystals serve the function of making the leaf surface present hydrophobic property, but the wax crystals play an extremely important role. The theoretical model proposed based on the Cassie-Baxter equation can adequately elucidate the hydrophobic mechanism of leaf surface in Hylotelephium erythrostictum, and provides theoretical support for the bionic fabrication of superhydrophobic surface.