Experimental Investigation of Evaporating Sessile Droplets on PDMS Surface
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摘要: 利用粒子跟踪测速(particle tracking velocimetry, PTV) 技术,研究了聚二甲基硅氧烷(polydimethylsiloxane, PDMS)表面上的液滴蒸发行为.发现固液界面上的荧光微球首先向固液界面中心移动,而后发生运动反转,向三相接触线移动.其原因是由于接触线钉扎时接触线附近的蒸发通量较小,从而引起向液滴中心的流动,这种流动将微球带向液滴中心.理论分析了三相接触线的移动特征,发现其移动速度理论值与实验值在同一量级,而移动加速度的实验值较理论值偏大,造成这种偏差的原因是三相接触线处的荧光微球削弱了基底对三相接触线的钉扎作用.Abstract: Evaporation of sessile water droplets on polydimethylsiloxane (PDMS) surface was experimentally studied with the particle tracking velocimetry (PTV) technique. The fluorescent microspheres at the solid-liquid interface first moved towards the center and then back to the contact line. Because the evaporative flux near the contact line is less than that far from the line, there will be a capillary flow towards the center when the contact line is pinned. Such a flow will carry microspheres towards the center. Moving characteristics of the contact line were also investigated. It is found that the theoretical values of the moving velocity at different moments in the CCA stage is of the same order with the experimental values. However, the experimental moving accelerations were much larger than the theoretical ones because the microspheres at the contact line weaken the interaction between the PDMS surface and the contact line.
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Key words:
- droplet /
- evaporation /
- PDMS /
- contact line /
- PTV technique
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[1] 赵亚溥. 表面与界面物理力学[M]. 北京: 科学出版社, 2012.(ZHAO Ya-pu. Physical Mechanics of Surface and Interface [M]. Beijing: Science Press, 2012.(in Chinese)) [2] Picknett R G, Bexon R. The evaporation of sessile or pendant drops in still air[J]. Journal of Colloid and Interface Science,1977,61(2): 336-350. [3] Deegan R D, Bakajin O, Dupont T F, et al. Capillary flow as the cause of ring stains from dried liquid drops[J]. Nature,1997,389: 827-829. [4] ZHAO Ya-pu. Moving contact line problem: advances and perspectives[J]. Theoretical and Applied Mechanics Letters,2014,4(3): 034002. [5] Hu H, Larson R G. Marangoni effect reverses coffee-ring depositions[J]. Journal of Physical Chemistry B,2006,110(4): 7090-7094. [6] Hu H, Larson R G. Analysis of the microfluid flow in an evaporating sessile droplet[J]. Langmuir,2005,21(9): 3963-3971. [7] Petsi A J, Burganos V N. Evaporation-induced flow in an inviscid liquid line at any contact angle[J]. Physical Review E,2006,73(4): 041201. [8] Berteloot G, Pham C T, Daerr A, et al. Evaporation-induced flow near a contact line: consequences on coating and contact angle[J]. Europhysics Letters,2008,83(1): 14003. [9] Gelderblom H, Bloemen O, Snoeijer J H. Stokes flow near the contact line of an evaporating drop[J]. Journal of Fluid Mechanics,2012,709: 69-84. [10] Dhavaleswarapu H K, Migliaccio C P, Garimella S V, et al. Experimental investigation of evaporation from low-contact-angle sessile droplets[J]. Langmuir,2010,26(2): 880-888. [11] Dash S, Chandramohan A, Garimella S V. Flow visualization during droplet evaporation on hydrophobic and superhydrophobic surfaces[J]. Journal of Heat Transfer,2014,136(8): 080917. [12] Pan Z H, Dash S, Weibel J A, et al. Assessment of water droplet evaporation mechanisms on hydrophobic and superhydrophobic substrates[J]. Langmuir,2013,29(51): 15831-15841. [13] WANG Zi-qian, ZHAO Ya-pu. In situ observation of thermal Marangoni convection on the surface of a sessile droplet by infrared thermal imaging[J]. Journal of Adhesion Science and Technology,2012,26(12/17): 2177-2188. [14] Christy J R E, Hamamoto Y, Sefiane K. Flow transition within an evaporating binary mixture sessile drop[J]. Physical Review Letters,2011,106(20): 205701. [15] Hamamoto Y, Cheristy J R E, Sefiane K. The flow characteristics of an evaporating ethanol water mixture droplet on a glass substrate[J]. Journal of Thermal Science and Technology,2012,7(3): 425-436. [16] HE Ming-hao, QIU Hui-he. Internal flow patterns of an evaporating multicomponent droplet on a flat surface[J]. International Journal of Thermal Sciences,2016,100: 10-19. [17] Ido T, Murai Y, Yamamoto F. Postprocessing algorithm for particle-tracking velocimetry based on ellipsoidal equations[J]. Experiments in Fluids,2002,32(3): 326-336. [18] ZHENG Xu, KONG Gao-pan, Silber-Li Zhan-hua. The influence of nano-particle tracers on the slip length measurements by microPTV[J]. Acta Mechanica Sinica,2013,29(3): 411-419. [19] Stauber J M, Wilson S K, Duffy B R, et al. Evaporation of droplets on strongly hydrophobic substrates[J]. Langmuir,2015,31(12): 3653-3660. [20] 徐国旺, 廖明朝. 拟合圆的几种方法[J]. 武汉工业学院学报, 2002(4): 104-106.(XU Guo-wang, LIAO Ming-chao. A varity of methods of fit circle[J]. Journal of Wuhan Polytechnic University,2002(4): 104-106.(in Chinese)) [21] YU Ying-song, WANG Zi-qian, ZHAO Ya-pu. Experimental and theoretical investigations of evaporation of sessile water droplet on hydrophobic surfaces[J]. Journal of Colloid and Interface Science,2012,365(1): 254-259. [22] Weast R C, Astle M J. CRC Handbook of Chemistry and Physics [M]. 62nd ed. Boca Raton, FL: CRC Press, 1981.
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