叶片表面微细观结构对润湿性的影响

目的 探究叶片表面微细观结构对其润湿性的影响因素，以及控制机理。方法 以银杏（Ginkgo biloba,G. biloba）、二乔玉兰（Magnolia soulangeana, M. soulangeana）和二球悬铃木（Platanus acerifolia, P. acerifolia）3种处于落叶期初段的叶片样本为研究对象，测量3种叶片正背面的接触角，结合环境扫描电子显微镜图像，对比分析不同叶片正面和背面微细观结构及其对接触角的影响。结果 实验结果表明，落叶期初段银杏、二乔玉兰和二球悬铃木叶片正面均表现出弱亲水性，接触角分别为54.40°～66.80°、57.93°～74.87°、55.73°～82.23°。在银杏叶片背面，无论是顺纹理还是逆纹理方向，均表现出疏水特征，顺纹理方向的接触角为122.63°～135.10°，逆纹理方向的接触角为103.03°～134.13°。二乔玉兰和二球悬铃木的背面为中性润湿，接触角分别为82.87°～96.37°、90.50°～97.47°。结论 不同类型叶片的表面微结构显著不同，同种类型叶片正背面微结构也表现出较大差异。3种叶片背面接触角均...

Effect of Leaf Surface Microstructure on Wettability

Understanding wettability property of a solid material is crucial in surface processing technology and surface engineering. Previous researches show that the wettability of a material is far from a constant value but influenced by the environmental factors such as temperature and humidity, and the surface roughness such as surface microstructure and hierarchical structures. Recent bionics studies, such as the nearly spherical droplet on lotus leaf and the upward water transport on the peristome surface of Nepenthes alata, have inspired researchers to understand the affecting factors on the surface wettability and thus develop artificial surfaces with practical applications. The microstructure of a material surface, especially the hierarchical microstructure or the multiscale microstructure, is one of the main factors affecting the wettability. However, a leaf at its different growth stages shows varied wettability. Moreover, the wettability of upper surface and backside surface of the same leaf usually shows notable difference. There is still not a consensus of the controlling mechanism of leaf surface microstructure on its wettability. In this study, the contact angle on the upper surface and backside surface of Ginkgo biloba, Magnolia soulangeana and Platanus acerifolia leaves in their early deciduous period was measured. Combined with the multiscale microstructure observation by environmental scanning electron microscopy (ESEM), the effect of leaf surface microstructure on wettability was investigated. The typical microstructures on the upper surface and backside surface of the leaves at different scales were characterized firstly. Then, the effect of leaf surface microstructure on wettability was investigated. The basic assumption was that the material property of the upper surface and backside surface of one leaf was the same. It was found that the upper surfaces of the three plants leaves showed weak hydrophilicity in their early deciduous period, the contact angles ranged from 54.40°-66.80°, 57.93°-74.87° and 55.73°-82.23° respectively. The backside surface of Ginkgo biloba leaf showed hydrophobic characteristics along the directions in parallel and perpendicular to the texture directions and the contact angles ranged from 122.63°-135.10° and 103.03°-134.13° respectively. The backside surfaces of Magnolia soulangeana and Platanus acerifolia leaves showed neutral wettability and the contact angles ranged from 82.87°-96.37° and 90.50°-97.47° respectively. As the ESEM results show, the microstructures in the leaves of the three investigated plants exhibit large differences. For the same leaf, the microstructure morphologies in its upper side surface and backside surface show distinct differences, especially for the Ginkgo biloba. The difference between the leaf microstructures is thus considered as the main reason that leads to the distinct wettability between the upper surface and backside surface. Higher levels of microstructure complexities in the backside surface of leaves, such as the stoma structures, account for the higher contact angles measured on the backside surface for the three kinds of leaves. Among them, the contact angle measured on the backside surface of Ginkgo biloba leaf is much larger than that on its upper surface. It is considered that the hierarchical microstructure in the backside surface of Ginkgo biloba leaf leads to its hydrophobic property, even though its upper surface shows weak hydrophilicity. The study elaborates the effects of microstructure on wettability, which can shed light on the design and fabric of biomimetic multifunctional surfaces for different wettability needs.