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To acquire the unique behavioral characteristics that droplets impact the Janus particle (amphiphilicity) sphere surface, a series of collision experiments is conducted by using Janus particles with a diameter of 5.0 mm. These Janus particles are prepared by chemical treatment of the copper particles. Water droplets with a diameter of 2.0 mm are used to impact hydrophbilic surface, hydrophobic surface and hydropholic-hydropholic boundary of Janus particle, under four Weber numbers which are 2.7, 10, 20 and 30, the corresponing Reynold numbers are 621.8, 1191.9, 1589.2 and 2185.1. The results show that the collision process can be divided into four stages: spread, retraction, oscillation and rebound. Under different Weber numbers, the behavioral characteristics of droplets are mainly affected by the surface wettability. On the hydrophbilic surface, the droplets exhibit the spreading characteristics, with increasing time the spreading coefficient gradually increases and finally tends to be stable. As Weber number increases, the difference in spreading coefficient for droplet under adjacent Weber number gradually decreases, indicating that droplets spreading is mainly affected by inertia. On the hydrophobic surface, the spreading coefficient on the figure presents a "parabola" shape. Droplets spreading takes the same time to reach the maximum spreading coefficient under different Weber numbers. However, when droplets impact the hydropholic-hydropholic boundary, droplets show spreading and rebound behavioral characteristics simultaneously. At the beginning of droplets spreading, the spreading coefficient has almost the same value on both sides of the hydropholic-hydropholic boundary. With the increase of time, part of droplets on the hydrophobic are attracted by the hydrophbilic side surface and go into hydrophbilic side zone. In order to explain this phenomenon, the concept of line tension is introduced and the line tension on the hydrophilic side is found to be less than that on the hydrophobic side by analyzing the forces on both sides of the droplets. Based on energy balance and force analysis, it is found that the mutual conversion of droplet kinetic energy and surface energy are the key factor to make droplets spread. The droplets possess the unique behavioral characteristics and reach an equilibrium state under the combined influence of gravity, inertial force, surface tension, viscous force, and contact force.
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Keywords:
- wettability /
- droplet /
- collision /
- Janus particle
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Yang W L 2017 Ph. D. Dissertation (Beijing: North China Electric Power University) (in Chinese)
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图 1 液滴碰撞球面实验装置系统 1. 计算机; 2. 高速摄影仪; 3. 微流量液滴控制器; 4. Janus球; 5. 可调节底柱
Figure 1. Experimental set up of the droplet collision on spherical surface. 1. Computer; 2. high speed camera; 3. digitized microliter droplet dispenser; 4. Janus sphere; 5. adjustable bottom column.
图 2 不同We下液滴碰撞疏水侧球面行为的动态过程
Figure 2. Dynamic behavior of droplet collision on the hydrophobic spherical surface under different We
图 3 不同We下的动态铺展因子变化(疏水侧)
Figure 3. Dynamic spreading factor of droplet collision under different We (hydrophobic side).
图 4 不同We下液滴碰撞亲水侧球面行为的动态过程
Figure 4. Dynamic behavior of droplet collision on the hydrophilic spherical surface under different We.
图 5 不同We下的动态铺展因子变化(亲水侧)
Figure 5. Dynamic spreading factor of droplet collision under different We (hydrophilic side).
图 6 不同We下液滴碰撞亲疏水分界线行为的动态过程
Figure 6. Dynamic behavior of droplet collision on the hydrophilic-hydrophobic boundary under different We.
图 7 不同We下的动态铺展因子变化 (亲疏水分界线) (a) 液滴在Janus亲水侧的变化; (b) 液滴在Janus疏水侧的变化
Figure 7. Dynamic spreading factor of droplet collision under different We (the hydrophilic-hydrophobic boundary): (a) Dynamic spreading factor of droplet on the hydrophilic side; (b) dynamic spreading factor of droplet on the hydrophobic side.
图 8 液滴在疏水侧、亲水侧和亲疏水分界线的受力
Figure 8. Force analysis of the droplet on the hydrophobic side, hydrophilic side and hydrophilic-hydrophobic boundary.
图 9 球面的线张力效应
Figure 9. Line tension effect of sphere.
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[1] Kim S Y, Choi B G, Baek W K, Park S H, Park S W, Shin J W 2019 Smart Mater. Struct. 28 035025
Google Scholar
[2] Derby B 2010 Annu. Rev. Mater. Sci. 40 395
Google Scholar
[3] Zhou Z F, Chen B, Wang R, Wang G X 2017 Exp. Therm. Fluid Sci. 82 189
Google Scholar
[4] Gyeongrak C, Jong L, Ju C, Young J K, Yeon S C, Mark S Chang M, Kwon L, Sung K, Inpil K 2016 Sensors. 16 1171
Google Scholar
[5] Aguilar G, Vu H, Nelson J S 2004 Phys. Med. Biol. 49 147
Google Scholar
[6] 代超, 纪献兵, 周冬冬, 王野, 徐进良 2018 浙江大学学报(工学版) 1 36
Google Scholar
Dai C, Ji X B, Zhou D D, Wang Y, Xu J L 2018 Journal of Zhejiang Univ. (Engineering Science). 1 36
Google Scholar
[7] Kawahara N, Kintaka K, Tomita E 2017 Spie. 10328 1032817
Google Scholar
[8] Rioboo R, Voue M, Vaillant A, Coninck D J 2008 Langmuir. 24 14074
Google Scholar
[9] Biance A L, Clanet C, Quéré D 2004 Phys. Rev. E. 69 016301
Google Scholar
[10] Josserand C, Thoroddsen S T 2016 Annu. Rev. Fluid Mech. 48 365
Google Scholar
[11] Hamlett C A E, Atherton S, Shirtcliffe N J, Mchale G, Ahn S, Doerr S H 2013 Eur. J. Soil. Sci. 64 324
Google Scholar
[12] Kang B S, Lee D H 2000 Exp. Fluids. 29 380
Google Scholar
[13] 毕菲菲, 郭亚丽, 沈胜强, 陈觉先, 李熠桥 2012 61 293
Google Scholar
Bi F F, Guo Y L, Shen S Q, Chen J X, Li Y Q 2012 Acta. Phys. Sin. 61 293
Google Scholar
[14] 郑志伟, 李大树, 仇性启, 朱晓丽, 崔运静 2015 化工学报 5 48
Google Scholar
Zheng Z W, Li D S, Qiu X Q, Zhu X L, Cui Y J 2015 J. Chem. Ind. Eng. 5 48
Google Scholar
[15] Khurana G, Sahoo N, Dhar P 2019 Phys. Fluids. 31 072003
Google Scholar
[16] Amirfazli A, Banitabaei S A 2017 Phys. Fluids. 29 419
Google Scholar
[17] Bakshi S, Roisman I V, Tropea C 2007 Phys. Fluids. 19 032102
Google Scholar
[18] Gennes D P G 1992 Rev. Mod. Phys. 64 645
Google Scholar
[19] Mitra S, Nguyen T B, Doroodchi E, Pareek V, Joshi J B, Evans G M 2016 Chem. Eng. Sci. 149 181
Google Scholar
[20] 杨卧龙 2017 博士学位论文 (北京: 华北电力大学)
Yang W L 2017 Ph. D. Dissertation (Beijing: North China Electric Power University) (in Chinese)
[21] Clanet C, BéGUIN, CéDRIC, Richard D, QUéRé D 2004 J. Fluid Mech. 517 199
Google Scholar
[22] Khojasteh D, Bordbar A, Kamali R, Marengo M 2017 Int. J. Comput. Fluid D. 31 310
Google Scholar
[23] 汪焰恩, 周金华, 秦琰磊, 李鹏林, 杨明明, 韩琴, 王月波, 魏生民 2012 振动与冲击 31 51
Google Scholar
Wang Y E, Zhou J H, Qing Y L, Li P L, Yang M M, Han Q, Wang Y B, Wei S M 2012 J. Vib. Shock. 31 51
Google Scholar
[24] 王辉 2013硕士学位论文 (大连: 大连理工大学)
Wang H R 2013 M. S. Thesis (Dalian: Dalian University of Technology) (in Chinese)
[25] Yasmin D, Mitra S, Evans G M 2019 Miner. Eng. 131 111
Google Scholar
[26] Gennes P G D 1985 Rev. Mod. Phys. 57 827
Google Scholar
[27] Gibbs J W 1948 Nature. 124 119
Google Scholar
[28] Pethica B A 1977 J. Colloid Interf. Sci. 62 567
Google Scholar
[29] Guzzardi L, Rosso R 2007 J. Food Compos. Anal. 40 19
Google Scholar
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