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受自然界启发, 仿生微结构被广泛用于调控固-液界面的性质. 研究显示, 液滴在微结构表面的各向异性浸润行为可用于实现微流动方向和速度的控制, 且其各向异性浸润与微结构的尺寸和分布等密切相关. 本文研究了微矩形凹槽尺寸对液滴各向异性浸润行为的影响规律. 结果显示, 液滴沿平行沟槽的方向具有较小的运动阻力、易铺展, 因此具有较小接触角; 而垂直于沟槽方向, 由于沟槽的阻隔作用具有较大运动阻力, 因而具有较大接触角, 并且在垂直方向液滴的浸润过程是三相线一系列钉扎和跳跃行为. 在微矩形凹槽表面, 液滴沿平行方向接触角θ//与肋板宽度R和凹槽宽度G密切相关, 其值与表面固体面积比成反比; 而垂直于沟槽方向的接触角θ⊥随肋板宽度R和凹槽宽度G变化基本保持不变. 同时各向异性液滴的变形比L/W、特征方向接触角比值θ⊥/θ// 与表面固体面积比成正比. 研究结果有助于加深理解微结构表面浸润行为的机制, 并为微矩形凹槽在微流动控制方向的应用提供技术支持.Biomimetic microstructure has been used widely in the fields of microfluidics, micro-mixers, flow drag reduction, tribology, etc. When solid surface is modified with microstructure, it will inevitably influence the solid-liquid interfacial behaviors, such as adhesion, surface wetting, shear viscous resistance, and interfacial slip. Surface anisotropic wetting can be achieved by using either of anisotropic surface microstructure and chemically heterogeneous patterned surface, or both of them. And anisotropic wetting properties can be used to control the micro-flowing behaviors, like mixing, flowing direction and speed. The effect of microstructure on the surface wetting behavior is closely related to the size, shape and arrangement of microstructure. In the paper, the influence of micro-groove size on liquid anisotropic wetting behavior is studied. The results indicate that the droplet wetting state of the patterned surface used is Cassie state. According to the experimental results, we can see that the liquid flows easily along the groove direction with small motion resistance, thus resulting in a small contact angle. While the water droplet has a higher flowing resistance in the direction perpendicular to the groove direction due to the energy barrier caused by micro-groove, thus showing a larger contact angle. Meanwhile, the water droplet shows pinning and jump behavior during the spreading in the direction perpendicular to the micro-groove direction. The contact angle along the micro-groove direction θ// increases with groove width G increasing, and decreases with ridge width R increasing, which means that the parallel direction contact angle θ// is inversely proportional to the solid fraction R/(R + G). And the experimental contact angle θ// shows good consistence with that obtained from theoretical Cassie model. While the contact angle of water droplet perpendicular to groove direction θ⊥ almost keeps no change with groove width G nor ridge width R. Both the droplet deformation ratio L/W and contact angle ratio of the two featured direction θ⊥/θ// are proportional to the solid fraction R/(R + G). The water droplet shows anisotropic wetting behaviors, which means that the liquid motion resistances are different in these directions. The high droplet deformation ratio L/W and the high contact angle ratio θ⊥/θ// correspond to the large difference in motion resistance. And surface wetting behavior has a great influence on the micro-flowing behavior. Thus, the micro-flowing behavior can be regulated by changing the microgroove size. The present research can conduce to the understanding the wetting mechanism and flowing behaviors of liquid droplet on patterned surface.
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Keywords:
- micro-groove /
- anisotropic wetting /
- contact angle /
- pinning effect
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图 1 微矩形凹槽结构示意图(a)及实际被测表面的SEM图(b)
Fig. 1. Schematic diagram of (a) micro-rectangular-groove surface and (b) the SEM images of the tested surface.
图 2 微矩形凹槽表面各向异性浸润行为
Fig. 2. Anisotropic wetting behavior on micro-rectangular-groove surface.
图 3 (a)实验测试装置示意图; (b)表面各向异性接触角表征
Fig. 3. (a) Schematic diagram of experimental tool; (b) the description of surface anisotropic wetting contact angle.
图 5 (a)微矩形凹槽宽度和(b)肋板宽度对液滴浸润行为的影响
Fig. 5. Influences of the groove width (a) and ridge width (b) of micro-rectangular-groove on the surface wetting behavior.
图 6 微结构表面固体面积比对接触角的影响
Fig. 6. Influences of solid fraction on surface anisotropic contact angle.
图 7 微结构表面液滴接触角各向异性和变形比变化规律
Fig. 7. Influences of solid fraction on the ratio of θ⊥/θ// and droplet deformation ratio L/W.
图 8 9#微结构表面液滴前进过程的实验结果(a)−(e)及示意图(f)和(g)
Fig. 8. Experimental results (a)−(e) and schematic diagrams (f) and (g) of droplet moving processes on 9# micro-rectangular groove surface.
表 1 微矩形凹槽的尺寸参数
Table 1. Parameters of micro-rectangular grooves used in the experiments.
序号 G/μm R/μm D/μm Solid fraction
R/(R + G)1 5 5 19 0.50 2 7 5 19 0.42 3 9 5 19 0.36 4 11 5 19 0.31 5 13 5 19 0.28 6 9 7 19 0.44 7 9 9 19 0.50 8 9 11 19 0.55 9 9 13 19 0.59 
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[1] Jokerst J C, Emory J M, Henry C S 2012 Analyst 137 24
Google Scholar
[2] Ballerini D R, Li X, Shen W 2012 Microfluid Nanofluid 13 769
Google Scholar
[3] Sharma R, Ragavan K V, Thakur M S, Raghavarao K S M S 2015 Biosens. Bioelectron. 74 612
Google Scholar
[4] 蒋成刚 2014 博士学位论文 (大连: 大连理工大学)
Jiang C G 2014 Ph. D. Dissertation (Dalian: Dalian University of Technology) (in Chinese)
[5] 张慧 2014 硕士学位论文 (苏州: 苏州大学)
Zhang H 2015 M. S. Thesis (Suzhou: Soochow University) (in Chinese)
[6] 王铁强 2013 博士学位论文 (长春: 吉林大学)
Wang T Q 2013 Ph. D. Dissertation (Changchun: Jilin university) (in Chinese)
[7] 蔡东海, 汪前彬, 赵天艺, 刘欢, 江雷 2014 化学通报 77 743
Cai D H, Wang Q B, Zhao T Y, Liu H, Jiang L 2014 Chemistry 77 743
[8] 乔小溪, 张向军, 田煜, 孟永钢 2017 66 044703
Google Scholar
Qiao X X, Zhang X J, Tian Y, Meng Y G 2017 Acta. Phys. Sin. 66 044703
Google Scholar
[9] 王鹏伟, 刘明杰, 江雷 2016 65 186801
Google Scholar
Wang P W, Liu M J, Jiang L 2016 Acta. Phys. Sin. 65 186801
Google Scholar
[10] Yang F C, Chen X P 2019 Chin. Phys. B 28 044701
Google Scholar
[11] Liu S S, Zhang C H, Zhang H B, Zhou J, He J G, Yin H Y 2013 Chin. Phys. B 22 106801
Google Scholar
[12] Chung J Y, Youngblood J P, Stafford C M 2007 Soft Matter 3 1163
Google Scholar
[13] Priezjev N V 2011 J. chem. Phys. 135 204704
Google Scholar
[14] Kim T I, Suh K Y 2009 Soft Matter 5 4131
Google Scholar
[15] Kim G H, Lee B H, Im H, Jeon S B, Kim D, Seol M L, Hwang H, Choi Y K 2016 RSC Adv. 6 41914
Google Scholar
[16] Chu K H, Xiao R, Wang E N 2010 Nat. Mater. 9 413
Google Scholar
[17] Wang S L, Yu N Z, Wang T Q, Ge P, Ye S S, Xue P H, Liu W D, Shen H Z, Zhang J H, Yang B 2016 ACS Appl. Mater. Interfaces 8 13094
Google Scholar
[18] Zhao Y, Lu Q H, Li M, Li X 2007 Langmuir 23 6212
Google Scholar
[19] Xia D Y, Brueck S R J 2008 Nano Lett. 8 2819
Google Scholar
[20] Yildirim A, Yunusa M, Ozturk F E, Kanik M, Bayindir M 2014 Adv. Funct. Mater. 24 4569
Google Scholar
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