| WANG Xiang-han,WAN Yan-ling,CHU Shun-shun,XU Jin-kai,WU Qing-tang.Directional Droplet Movement Based on Spatial Quadric Pyramid Composite Surface[J],52(9):351-357, 407 |
| Directional Droplet Movement Based on Spatial Quadric Pyramid Composite Surface |
| Received:August 18, 2022 Revised:November 01, 2022 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.09.031 |
| KeyWord:WEDM brass step-by-step etching self-driven movement composite gradient Laplace pressure |
| Author | Institution |
| WANG Xiang-han |
School of Mechanical and Electrical Engineering, Changchun University of Science and Technology, Changchun , China;Key Laboratory of Cross-scale Micro and Nano Manufacturing, Changchun , China |
| WAN Yan-ling |
School of Mechanical and Electrical Engineering, Changchun University of Science and Technology, Changchun , China;Key Laboratory of Cross-scale Micro and Nano Manufacturing, Changchun , China |
| CHU Shun-shun |
School of Mechanical and Electrical Engineering, Changchun University of Science and Technology, Changchun , China |
| XU Jin-kai |
Key Laboratory of Cross-scale Micro and Nano Manufacturing, Changchun , China |
| WU Qing-tang |
Changchun Institute of Equipment and Process, Changchun , China |
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| Abstract: |
| Directional movement of liquids has a wide range of applications in fog collection, oil-water separation, microfluidics, condensation and heat exchange, protein adsorption, and cell migration. It is found that organisms such as cactus spines and spider silk have the ability to drive the directional movement of liquid droplets due to the presence of structural gradients on the surface. Inspired by this, a composite structure surface is prepared in this work. Wire electrical discharge machining (WEDM) was used to prepare a tetragonal structure on the surface of H62 brass, and wetting gradient was prepared on tetragonal surface by the stepwise chemical etching. 500 mL NaOH solution with a concentration of 2.67 mol/L was mixed with 500 ml ammonium persulfate solution with a concentration of 0.15 mol/L. The cone tip of the pyramid structure was vertically fixed at the bottom of the container, and the computer program was used to control the power device to push the syringe every 20 min to inject the same amount of mixed solution to complete the construction of the wetting gradient. Thus, the unbalanced surface tension provided by the wetting gradient and the Laplace pressure formed by the structural gradient formed a driving force, making the droplets exhibit stronger motion performance than a single gradient surface. Scanning electron microscope and high-speed camera were used to observe the microstructure of the composite surface and the movement of droplets on the surface of the specimen, respectively. At the same time, the effect laws of the lateral angle and other factors on the droplet directional movement were compared and analyzed. Under the action of the structural gradient of the unetched surface, the driving force of the droplet decreased with the increase of the angle β, so the droplet moving distance was negatively correlated with the angle β. After a certain wetting gradient was given to the surface, at the same position from the tip, the side width of the specimen increased with the increase of the angle β, so that the unbalanced tension of the wetting gradient on the droplet also increased. Therefore, compared with the unetched pyramid surface, the movement distance of the composite surface droplets increased significantly, and the increase of the droplet movement distance was positively correlated with the angle β. Finally, under the combined action of structural gradient and wetting gradient, the directional movement distance of droplets on the surface of the specimen with β=5° reached the maximum, and the maximum movement distance Lmax=6.96 mm. In conclusion, the composite surface preparation method that can maximize the droplet movement distance is explored, and the directional movement performance of droplets on the surface and its affecting factors are also studied. Compared with the single gradient surface, the composite droplet directional movement surface can obtain the longest movement distance. The preparation method of wire electrical discharge machining and chemical etching is simple and low cost, which is helpful to promote the preparation of large quantities of researches on directional movement of droplet based on composite surface, showing a good application prospect. |
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