| ZHANG Jin-hong,SHI Kui,XU Peng,LI Qian,XUE Long-jian.Characterization of Classical Biological Surfaces with Special Wettabilities by Liquid-Solid Friction Force[J],50(7):187-193 |
| Characterization of Classical Biological Surfaces with Special Wettabilities by Liquid-Solid Friction Force |
| Received:October 16, 2020 Revised:February 14, 2021 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2021.07.019 |
| KeyWord:surface wettability contact angle sliding angle friction force MPCP |
| Author | Institution |
| ZHANG Jin-hong |
School of Power and Mechanical Engineering, Wuhan University, Wuhan , China;Department of Mechanical Engineering, Shanxi Polytechnic College, Taiyuan , China |
| SHI Kui |
School of Power and Mechanical Engineering, Wuhan University, Wuhan , China |
| XU Peng |
School of Power and Mechanical Engineering, Wuhan University, Wuhan , China |
| LI Qian |
School of Power and Mechanical Engineering, Wuhan University, Wuhan , China |
| XUE Long-jian |
School of Power and Mechanical Engineering, Wuhan University, Wuhan , China |
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| Abstract: |
| Contact angle and sliding angle are usually used to characterize the wettability of solid surfaces, though the technique has its own inherent limitations. In the current work, a newly established technique for the measurement of liquid-solid interfacial friction is employed to quantitatively characterize the classical biological surfaces with superwettabilities, including lotus leaves, rose petals and butterfly wings. The liquid-solid friction forces of these classical surfaces are characterized by the technique of MPCP (monitoring the projection of capillary position). The influences of sample drying, size and moving velocity of water droplet on the liquid-solid friction force are also discussed. When the droplet volume is increased from 2 μL to 10 μL, the static friction force, FS, of fresh lotus leaves increases from (10.01±0.75) μN to (15.99±1.99) μN, while the kinetic friction force, FK, slightly increases from (9.10±1.30) μN to (11.31±0.75) μN. The drying process increases both the FS and FK of lotus leaves that FS increases from (22.11±3.44) μN to (34.72±1.99) μN, and FK increases from (10.40±0.75) μN to (20.42±3.00) μN upon the increase of droplet volume. Different from lotus leaves, both FS and FK of rose petals increase significantly upon the droplet-volume increase, and are larger than that of the dried ones. Due to the anisotropic structures on butterfly wing, FS and FK along the DF direction of butterfly wings are significantly smaller than that along DO direction, facilitating the rolling off of water droplets. When the moving speed of the droplet increases from 0.05 mm/s to 2.05 mm/s, FS and FK do not change obviously; in contrast, FS of fresh rose petals decreases from (70.22±1.99) μN to (60.21±1.99) μN, and FK significantly decreases from (44.21±2.25) μN to (18.21±1.30) μN, while FS and FK of dried rose petals slightly decreases. The velocity dependence on butterfly wings shows directional dependence that FS and FK along DF direction are almost constant and significantly decreased in the opposite direction DO. The MPCP technology has the capability to reveal all the detailed features of a friction process and to quantitatively characterize the wettability of solid surfaces. It overcomes the drawbacks of the measurement of sliding angle which measures the instant force when water droplet starts to sliding. Moreover, the quantitative characterization of the influences of the sample drying, size and moving velocity of water droplet on the liquid-solid friction force is helpful to reveal the scientific rules that cannot be revealed by the tests of contact angle and rolling angle. |
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