| HU Qin,YANG Hang,JIANG Xing-liang,SHU Li-chun.Wettability Recovery Mechanism of Natural Superhydrophobic Surface after Icing Damage[J],52(9):306-312 |
| Wettability Recovery Mechanism of Natural Superhydrophobic Surface after Icing Damage |
| Received:September 05, 2022 Revised:December 20, 2022 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.09.026 |
| KeyWord:icing environment superhydrophobicity wettability recovery mechanism |
| Author | Institution |
| HU Qin |
National Observation and Research Station for Xuefeng Mountain Energy Equipment Safety, Chongqing University, Chongqing , China |
| YANG Hang |
National Observation and Research Station for Xuefeng Mountain Energy Equipment Safety, Chongqing University, Chongqing , China |
| JIANG Xing-liang |
National Observation and Research Station for Xuefeng Mountain Energy Equipment Safety, Chongqing University, Chongqing , China |
| SHU Li-chun |
National Observation and Research Station for Xuefeng Mountain Energy Equipment Safety, Chongqing University, Chongqing , China |
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| Abstract: |
| In order to reveal the wettability recovery mechanism of the natural superhydrophobic surface after icing damage, lotus leaves were placed in a low-temperature and low-pressure artificial laboratory for the icing experiment. The icing test temperature was set to −5 ℃ and the wind speed was 1 to 3 m/s. The living lotus leaves were damaged by the cycle of "icing and deicing", and then recovered at room temperature. Wettability and roughness of the samples were measured by optical contact angle meter, digital tilt angle meter and 3D confocal microscope, respectively, to evaluate the wettability and surface roughness recovery process of lotus leaves after "icing and deicing" damage, and to analyze the recovery mechanism according to the characteristics of the recovery process. The static contact angle (WCA) decreased to 105.34°-123.07°, the slip angle (SA) increased to 39.5°-70.2°, the arithmetic average surface height (Sa) decreased to 3.123-2.624 μm, and the root mean square height (Sq) decreased to 3.542-3.113 μm, respectively. The wettability and roughness varied greatly from the initial values when a single "icing and deicing" cycle was carried out. As the number of cycles increased, the change gradually slowed down. In the subsequent action, the anchoring effect was not as strong as in the first cycle, so the surface roughness was not reduced as much as in the first cycle, and the change of wettability was not significant. For lotus leaves damaged once by the cycle of "icing and deicing", the WCA recovered to more than 150° after 48 hours. The SA dropped below 10° after recovery for 24 hours. About 72 hours after three cycles of "icing and deicing", WCA and SA returned to their initial values. After five cycles of "icing and deicing" damage, lotus leaves could not complete the recovery process. Although the absolute values of the surface roughness parameters are different after different cycles of "icing-deicing" damage, the recovery of surface roughness generally has an exponential function recovery process with time, which is consistent with the typical solid diffusion model. In particular, after multiple cycles of more severe damage, wettability has a short and sharp recovery phase at the initial stage, implying that there is a factor independent of diffusion, which is considered to be the cells re-expanded, and most living cells exhibit a weak temporal power-law viscoelastic deformation under mechanical loading. The shape of the cells can be recovered over time after the removal of the mechanical load. The viscoelasticity problem at the supracellular level can be explained by long-term mechanisms, with timescales ranging from tens of minutes to hours. The recovery process of WCA and SA on the lotus leaf surface is determined by two factors:the epidermal cells expanded again and the epidermal wax layer recovered. After plant survival and local surface damage, both WCA and SA are fully recovered. WCA is more dependent on the microscopic roughness formed by plant cells and the epidermal wax layer, while SA is more dependent on the nano-roughness attached to the microscopic roughness. SA is more dependent on the restoration of nano-roughness than WCA. |
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