| ZHENG Jiang-tao,YANG Yi-long,CHAI En-hao,LIU Qian,BIAN Yu-feng,JU Yang.Effect of Leaf Surface Microstructure on Wettability[J],52(7):288-298 |
| Effect of Leaf Surface Microstructure on Wettability |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.07.026 |
| KeyWord:microstructure wettability contact angle ESEM surface contact area |
| Author | Institution |
| ZHENG Jiang-tao |
State Key Laboratory for Fine Exploration and Intelligent Development of Coal Resources,Beijing , China;School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing , China |
| YANG Yi-long |
School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing , China |
| CHAI En-hao |
School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing , China |
| LIU Qian |
School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing , China |
| BIAN Yu-feng |
School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing , China |
| JU Yang |
State Key Laboratory for Fine Exploration and Intelligent Development of Coal Resources,Beijing , China;School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing , China |
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| Abstract: |
| 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. |
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