本研究採用固著液滴法(sessile drop method)，將純水液滴置於聚甲基丙烯酸酯(PMMA)與聚碳酸酯(PC)平板上，並從液滴內部緩慢抽出液體，藉由改變液體汲取的速度，繼而觀察三相線與接觸角之動態變化情形。
液滴被汲取的過程中會涉及接觸角與三相線的變化，我們將這些變化區分為三個階段，包含恆定接觸半徑(constant contact radius, CCR)階段、恆定接觸角(constant contact angle, CCA) 階段和混合(mixed mode)階段。以CCR階段而言，潤濕直徑為定值，三相線固定不動，而接觸角不斷下降；當接觸角不斷降低至某一程度時，三相線會開始向液滴內部移動，此時接觸角維持不變，潤濕直徑隨時間遞減，此階段我們稱為CCA；最後在液滴消失殆盡前，後退接觸角開始降低不再維持定值，潤濕直徑繼續隨時間遞減，我們稱之為混合階段。
實驗結果顯示三相線向液滴內部移動的速度越快，位於CCA階段的後退接觸角下降的越多，對於PMMA平板而言，液滴的後退接觸角降低約5o-10o左右，而對PC平板而言，液滴的後退接觸角約降低10o -20o，另外在研磨的PC平板上完全沒有發現CCA階段，因此我們無法測得純水液滴於研磨PC平板上之後退接觸角。

This experiment shows the influence of triple line retraction velocity on receding contact angle by using sessile drop method. The experiment was performed by dropping the liquid drops on polymer PMMA (polymethyl methacrylate) and PC (poly carbonate) substrates. The suction process was then performed to reduce the droplet volume by pumping out the liquid drop using syringe pump and needle. It was found that the contact angle change when the de-wetting velocity increase.
From the experimental results, we can observe there are three stages: constant contact radius (CCR mode), constant contact angle, (CCA mode) and the mixing stage (mixed mode).
In CCR stage the wetting diameter is constant but contact angle continue to decline, when the CCA stage the contact angle is nearly constant but wetting diameter decrease. Finally, both contact angle and wetting diameter are continue to decline and retreat constantly, we call this stage is mix stage. From this experiment, we observe that in CCA stage, the greater retraction velocity will resulting smaller contact angle.
The comparison between the experimental data and the theoretical models obtained from literatures was performed to verified our conclusion that the receding contact angle is caused by the interaction between liquid molecules and substrates or viscous dissipation.

1. M. Schneemilch, R. A. Hayes, J. G. Petrov, J. Ralston, “Dynamic Wetting and Dewetting of a Low-Energy Surface by Pure Liquids”, Langmuir, 14, 7047-7051 (1998) 2. H. Eral and J. Oh,” Contact angle hysteresis: a review of fundamentals and applications”, Colloid Polym. Sci. 291, 247 (2013).
3. P.-G. de Gennes,” Wetting: Statics and dynamics”, Rev. Mod. Phys. 57, 827 (1985).
4. P. G. Pittoni, C. C. Chang, T. S. Yu, S. Y. Lin,”Evaporation of water drops on polymer surfaces: Pinning, depinning and dynamics of the triple line”, Colloids Surfaces A Phys. Eng. Asp., 432, 89–98. (2013)
5. P. G. Pittoni, H.K. Tsao, S.Y. Lin,”Water drop impingement on graphite substrates with random dilute defects”, Exp. Therm. Fluid Sci., 53, 142-146 (2014) 6. ramé-hart Information on Contact Angle
(http://www.ramehart.com/contactangle.htm)
7. P.-G. de Gennes, F. Brochard-Wyart and D. Quéré, Capillarity and wetting phenomena: drops,bubbles, pearls, waves (Springer Science & Business Media, 2013).
8. T. A.H. Nguyen, A. V. Nguyen, M. A. Hampton, Z. P. Xu, L. Huang, V. Rudolph” Theoretical and experimental analysis of droplet evaporation on solid surfaces”, Colloids Surfaces A Phys. Eng. Asp. 323, 36–49. (2008)
9. L. M. Lander, L. M. Siewierski, W. J. Brittain and E. A. Vogler,”A Systematic Comparison of Contact Angle Methods” Langmuir, 9, 2237 (1993). 10. M. Strobel, C. S. Lyons, “An Essay on Contact Angle Measurements” Plasma Processes Polym., 8, 8 (2011)
11. Biolin Scientific (http://www.biolinscientific.com)
12. J. G. Petrov, J. Ralston, M. Schneemilch, R. A. Hayes,“Dynamics of Partial Wetting and Dewetting in Well-Defined Systems”, J. Phys. Chem. B, 107, 1634-1645 (2003)
13. M. Schneemilch, R. A. Hayes, J. G. Petrov, J. Ralston” Dynamic Wetting and Dewetting of a Low-Energy Surface by Pure Liquids” Langmuir, 14, 7047-7051 (1998)
14. R. Fetzer, M. Ramiasa, J. Ralston,” Dynamics of Liquid-Liquid Displacement”, Langmuir, 25, 8069 (2009)
15. R. Fetzer and J. Ralston,” Drops and Bubbles in Contact with Solid Surfaces” J. Phys. Chem. C, 113, 8888 (2009)
16. J.-B. Dupont, D. Legendre,” Numerical simulation of static and sliding drop with contact angle hysteresis”, J. Comput. Phys., 229, 2453–2478 (2010) 17. E. Dussan,” On the Spreading of Liquids on Solid Surfaces: Static and Dynamic Contact Lines”, Annu. Rev. Fluid Mech., 11, 371 (1979).
18. G. Strcim, M. Fredriksson, P. Stenius, B. Radoev,” Kinetics of Steady-State Wetting”, J. Colloid Interface Sci.,134, 107 (1990).
19. O. N. Tretinnikov, Y. Ikada,” Dynamic Wetting and Contact Angle Hysteresis of Polymer Surfaces Studied with the Modified Wilhelmy Balance Method ” Langmuir, 10, 1606 (1994)
20. M.-Y. Zhou, P. Sheng,” Dynamics of immiscible-fluid displacement in a capillary tube“, Phys. Rev. Lett., 64, 882 (1990)
21. W. Rose and R. Heins,” Moving interfaces and contact angle rate-dependency “, J. Colloid Sci., 17, 39 (1962)
22. M.E.R. Shanahan, C. Bourg,” Effects of evaporation on contact angles on polymer surfaces”, Int. J. Adhes. Adhes., 14, 201–205 (1994)
23. C. Bourges-Monnier, M. E. R. Shanahan, ”Influence of Evaporation on Contact Angle”, Langmuir, 11, 2820–2829 (1995)
24. N. R. Morrow, M. D. Nguyen,” Effect of Interface Velocity on Dynamic Contact Angles at Rough Surfaces “, J. Colloid Interface Sci.,89, 523 (1982)
25. C. Zhang, X. Zhu, L. Zhou, ” Morphology tunable pinning force and evaporation modes of water droplets on PDMS spherical cap micron-arrays” , Chem. Phys. Lett., 508, 134–138 (2011)
26. R. Cox,“The dynamics of the spreading of liquids on a solid surface. Part 1. Viscous flow”,J. Fluid Mech., 168, 169 (1986)
27. T. D Blake, J. M. Haynes,” Kinetics of liquid/liquid displacement” J. Colloid Interface Sci., 30, 421 (1969)
28. O. V. Voinov,” Hydrodynamics of wetting”, J. Fluid Dyn. , 11, 714 (1976)
29. V. E. B. Dusean” International Symposium on Contact Angles and Wetting Phenomena”, J. Adhesion, 31,2-4 (1990)
30. T. D. Blake,; J. C. Berg, , Ed.; Marcel Dekker: New York ,P 251, (1993)
31. P. G. Petrov, J. G. Petrov, ”A Combined Molecular-Hydrodynamic Approach to Wetting Kinetics”, Langmuir , 8, 1762-1767(1992)
32. 林佳慧，”離子型界劑吸附動力學探討暨固著液滴蒸發行為之研究”，國立台灣科技大學化學工程所碩士論文 (2014)
33. de Laplace’ P. S., Mechanique Celeste, Supplement to book, 10 (1806)
34. P. G. Pittoni, C.-H. Lin, T.-S. Yu, S.-Y. Lin,” On the Uniqueness of the Receding Contact Angle: Effects of Substrate Roughness and Humidity on Evaporation of Water Drops”, Langmuir, 30, 9346−9354 (2014)
35. 王任群，”液滴撞擊石墨和聚碳酸酯板之氣泡捕捉行為研究”，國立台灣科技大學化學工程所碩士論文 (2014)