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液滴在纳米结构表面的润湿模式研究(Dewetting, Cassie, Partial Wenzel及Wenzel)对强化冷凝、表面自清洁、油水分离等具有重要意义, 现有文献主要研究了液滴在微柱阵列纳米结构表面的润湿行为. 本文采用分子动力学模拟, 研究了纳米结构倾角及表面浸润性对氩液滴在铂固体壁面上润湿模式及其相互转换的影响, 采用了三种纳米结构, 其倾角分别为60° (倒梯形)、90° (长方形)及120° (正梯形); 以本征接触角θe表征表面浸润性. 研究表明, 当θe < 118°时, 液滴在纳米结构表面均呈Wenzel状态, 即液体向纳米结构缝隙完全渗透; 当118° < θe < 145°时, 倒梯形纳米结构有助于液滴保持Cassie状态, 即液体不向纳米结构缝隙渗透, 正梯形纳米结构容易使液滴形成Partial Wenzel状态, 即液体向纳米结构缝隙部分渗透. 分析表明, 三种纳米结构倾角对液滴润湿模式的影响及转换满足自由能最小原理. 本文工作揭示出采用倒置纳米结构, 可使液滴更好维持Cassie模式.The wetting modes of droplet on nanostructure surface including Cassie, Partial Wenzel, and Wenzel are of great importance in enhancing the condensation heat transfer, surface self-cleaning and oil-water separation. Previous studies focused mainly on the behaviors of droplets on the surface of nano-pillar structures. In this work, the wetting behaviors of argon nanodroplet on platinum surface is investigated by the molecular dynamics simulations. The effects of nanostructure geometry parameters and characteristic contact angle θe on the wetting mode and the transition between different modes are investigated. The three-dimensional simulation box includes a bottom wall containing trapezoid wires (TWs) with different geometry parameters and other five surfaces. The TWs are populated on the wall based on the array arrangement. The periodic boundary conditions are imposed on the four side surfaces of the simulation box. The base angles of the side surface of TW with respect to horizontal plane are chosen as 60° (inverted TW), 90° (rectangular pin fin) and 120° (TW), respectively. For all the three base angles, the nanostructure surface can be completely wetted by liquid, behaving as the Wenzel mode when θe < 118°, under which the gaps of nanostructures are filled with liquid. However, when the characteristic contact angle θe is in a range of 118°–145°, the base angles of nanostructures have different effects on wetting modes. The surface with inverted TWs (60° base angle) is conducive to keeping droplet in Cassie mode, in which the liquid does not penetrate into any gap of nanostructures. The surface with rectangular pin fins behaves as either Partial Wenzel mode or Cassie mode. The transition between the two modes takes place at θe ～130°. The surface with TWs (120° base angle) keeps the droplet in Partial Wenzel mode, in which the gaps of nanostructures are partially wetted by liquid. For θe larger than 145°, the dewetting process takes place on the surface of the nanostructure, in which the droplet leaves the solid surface. We conclude that the wetting modes on nanostructured surface satisfy the minimum surface energy principle. Our work discloses a new finding that the surface with inverted TWs is easy to maintain Cassie mode, which is good for dropwise condensation applications.
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Keywords:
- droplet /
- nano-structure /
- wetting mode /
- molecular dynamics
[1] 强伟丽 2018 硕士学位论文 (大连: 大连理工大学)
Qiang W L 2018 M. S. Thesis (Dalian: Dalian University of Technology) (in Chinese)
[2] Wen R F, Zhong L, Peng B L, Xu W, Ma X H 2015 Appl. Therm. Eng. 88 265
Google Scholar
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Google Scholar
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Zhang J J 2020 Ph. D. Dissertation (Anhui: University of Science and Technology of China) (in Chinese)
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Wang W H 2018 M. S. Thesis (Haerbin: Harbin Engineering University) (in Chinese)
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图 1 (a)初始状态下的模拟系统图; (b)系统俯视图; (c) 纳米结构示意图
Fig. 1. (a) Diagram of a simulated system in initial state; (b) top view of system; (c) schematic diagram of nanostructure.
图 2 (a) Cassie, (b) Partial Wenzel, (c) Wenzel润湿状态的示意图; (d)粗糙度因子r及相面积分数f确定的示意图
Fig. 2. Sketches for (a) Cassie, (b) Partial Wenzel and (c) Wenzel wetting states; (d) schematic diagram for determining roughness factor r and phase area fraction f.
图 3 (a)无量纲势能随粒子间距的变化曲线; (b)本征接触角随表面浸润性的变化曲线
Fig. 3. (a) Variation curves of dimensionless potential energy with particle spacing; (b) change curves of intrinsic contact angle with surface wettability.
图 4 液滴在粗糙表面上三种润湿模式下的(a)—(c)密度云图及(d)—(f)接触角
Fig. 4. (a)–(c) Density nephograms and (d)–(f) contact angles of droplets in three wetting modes on rough surfaces.
图 5 (a)—(c)当φ = 60°, 90°, 120°时, 不同θe的平衡状态位型图; (d) 当φ = 60°, 90°, 120°时, 渗透率随表面浸润性的变化曲线
Fig. 5. (a)–(c) Bitmaps of equilibrium states for different θe with φ = 60°, 90°, 120°; (d) permeability curves with surface wettability with φ = 60°, 90°, 120°.
图 6 (a)当φ = 60°, 90°, 120°时, 表观接触角随θe的变化曲线; (b)液体润湿凹槽数目随θe的变化曲线, 其中, φ = 90°和120°时的曲线完全重合; (c)液体原子渗入到凹槽的数量随θe的变化曲线; (d)液滴基底圆半径随θe的变化曲线
Fig. 6. (a) Curves of apparent contact angle with θe when φ = 60°, 90°, 120°; (b) change curves of the number of liquid wetting grooves with θe, where the curves at φ = 90° and 120° are completely coincident; (c) amount of liquid atoms entering the groove varies with θe; (d) change curves of the droplet base circle radius with θe.
图 7 (a)—(c)不同φ和θe下的理论自由能值; (d)—(f)不同φ和θe下接触角的变化
Fig. 7. (a)–(c) Theoretical free energy values under different φ and θe; (d)–(f) change of contact angle under different φ and θe.
表 1 三种粗糙表面对应的结构参数
Table 1. Structural parameters corresponding to three rough surfaces.
φ/(°) w /σ s /σ h /σ r f 60 6.9 4.6 4.025 1.758 0.283 90 6.9 4.6 4.025 1.660 0.283 120 6.9 4.6 4.025 1.509 0.283 
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[1] 强伟丽 2018 硕士学位论文 (大连: 大连理工大学)
Qiang W L 2018 M. S. Thesis (Dalian: Dalian University of Technology) (in Chinese)
[2] Wen R F, Zhong L, Peng B L, Xu W, Ma X H 2015 Appl. Therm. Eng. 88 265
Google Scholar
[3] Birbarah P, Miljkovic N 2017 Int. J. Heat Mass Transfer 114 1025
Google Scholar
[4] Neinhuis C, Barthlott W 1997 Ann. Bot. 79 667
Google Scholar
[5] Lin F, Li S H, Li Y S, Li H J, Zhang L J, Zhai J, Song Y L, Liu B Q, Jiang L, Zhu D B 2002 Adv. Mater. 14 24
Google Scholar
[6] Blossey R 2003 Nat. Mater. 2 301
Google Scholar
[7] Xie J, Xu J L, Shang W, Zhang K 2018 Int. J. Heat Mass Transfer 127 1170
Google Scholar
[8] Wenzel R N 1936 J. Ind. Eng. Chem. 28 988
Google Scholar
[9] Cassie A B D, Baxter S 1944 Trans. Faraday Soc. 40 546
Google Scholar
[10] Zhuang Y X, Hansen O, Knieling T, Wang C, Rombach P, Lang W, Benecke W, Kehlenbeck M, Koblitz J 2007 J. Microelectromech. Syst. 16 1451
Google Scholar
[11] Nishino T, Meguro M, Nakamae K, Matsushita M, Ueda Y 1999 Langmuir 15 4321
Google Scholar
[12] Li Y S, Quéré D, Lv C J, Zheng Q S 2017 Mono Super Mater. 114 3387
Google Scholar
[13] Fu T, Wu N N, Lu C, Wang J B, Wang Q L 2019 Mol. Simulat. 45 35
Google Scholar
[14] Shahraz A, Borhan A, Fichthorn K A 2013 Langmuir 29 11632
Google Scholar
[15] Chen S, Wang J, Chen D 2014 J. Phys. Chem. C 118 18529
Google Scholar
[16] Wang J J, Li T, Li Y F, Duan Y R, Jiang Y Y, Arandiyan H, Li H 2018 Molecules 23 2407
Google Scholar
[17] Mao Y, Chen C L, Zhang Y 2013 Appl. Phys. A 111 747
Google Scholar
[18] Saha J K, Matin M A, Jang J, Jang J 2013 Bull. Korean Chem. Soc. 34 1047
Google Scholar
[19] Li Q, Wang B, Chen Y, Zhao Z 2016 Chem. Phys. Lett. 662 73
Google Scholar
[20] Wang J, Chen S, Chen D 2015 Phys. Chem. Chem. Phys. 17 30533
Google Scholar
[21] Marmur A 2004 Langmuir 20 3517
Google Scholar
[22] He B, Patankar N A, Lee J 2003 Langmuir 19 4999
Google Scholar
[23] Bico J, Uwe T, Quéré D 2002 Colloids Surf., A 206 41
Google Scholar
[24] Shi B, Dhir V K 2009 J. Chem. Phys. 130 204715
Google Scholar
[25] Yong X, Zhang L T 2009 Langmuir 25 5045
Google Scholar
[26] Savoy E S, Escobedo F A 2012 Langmuir 28 16080
Google Scholar
[27] Wang Z, Lin K, Zhao Y 2019 Colloid Interface Sci. 552 563
Google Scholar
[28] Zhu C Q, Gao Y R, Huang Y Y, Li H, Meng S, Francisco J S, Zeng X C 2017 Nanoscale 9 18240
Google Scholar
[29] 章佳健 2020 博士学位论文 (合肥: 中国科学技术大学)
Zhang J J 2020 Ph. D. Dissertation (Anhui: University of Science and Technology of China) (in Chinese)
[30] Niu Z X, Huang T, Chen Y 2018 Front. Phys.-Beijng 13 137804
Google Scholar
[31] Nagayama G, Kawagoe M, Tokunaga A, Tsuruta T 2010 Int. J. Therm. Sci. 49 59
Google Scholar
[32] Chen J X, Chen W Y, Xie Y J, Wang Z G, Qin J B 2017 Appl. Surf. Sci. 396 1058
Google Scholar
[33] 王文辉 2018 硕士学位论文 (哈尔滨: 哈尔滨工程大学)
Wang W H 2018 M. S. Thesis (Haerbin: Harbin Engineering University) (in Chinese)
[34] Li W, Amirfazli A 2005 J. Colloid Interface Sci. 292 195
Google Scholar
[35] Shahraz A, Borhan A, Fichthorn A K A 2012 Langmuir 28 14227
Google Scholar
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