奈米尺度之液滴-柱與液滴-孔洞系統的潤濕現象

本篇論文研究目的為探討在奈米尺度及無接觸線遲滯的條件下，液滴-柱及液滴-孔洞此二系統之潤濕現象。在一平滑表面上，可觀察到一奈米液滴之隨機運動行為；然而，當此液滴接觸到平滑表面上一材質與表面相同的凸起長方柱狀物時，其自由移動之能力將被限制住。無論是在親液或疏液系統，皆可觀察到液滴與柱之間存在的相互吸引力。藉由對系統施加一外力，並利用受力液滴之位移值及施加外力值，便可計算出兩種液滴脫離柱過程(與液滴是否跨越柱相關)之能量變化圖。結果顯示，所施加外力之臨界值、位能井深度值，在親液系統時皆大於在疏液系統時之值。此外，在親液系統可觀察到液滴能穩定對稱地跨坐在柱正上方；然而此狀態在疏液系統卻變得非常不穩定。另一方面，在液滴-孔洞之研究上，液滴初始即被放置在此孔洞的正上方，而根據觀察，液滴是否完全地潤濕此孔洞之條件，取決於液滴之潤濕性(接觸角)、液滴體積、孔洞大小以及孔洞內部構造。結果顯示，液滴恰巧潤濕孔洞之臨界角，會隨著液滴體積增大或孔洞大小減小而逐漸降低；而此結果也可用於解釋為何在金字塔形孔洞及倒金字塔形孔洞能觀察到截然不同的潤濕行為。

關鍵字

潤濕；液滴；接觸角； Surface Evolver

並列摘要

The wetting behavior of a nanodrop encountering a nanoprotrusion and atop a nanogroove on a hysteresis-free surface is explored by Surface Evolver. On a smooth surface, a nanodrop exhibits random motion but will be captured as it encounters a nanoprotrusion, which possesses the same wettability as that of the surface. For both lyophilic and lyophobic systems, there exists an attraction between the drop and the protrusion. The energy profiles corresponding to the detaching processes with and without crossing the protrusion is determined by the displacement of the captured drop due to the applied external force. It is found that the critical forces and the depth of the energy wells of the lyophilic system are greater than those of the lyophobic system. Furthermore, the drop symmetrically straddling on the protrusion is stable for the lyophilic system but becomes unstable for the lyophobic system. For a nanodrop placed atop a nanogroove, whether the groove can be wetted by the drop depends on the wettability (contact angle), drop volume, groove size, and the shape of the groove. It is found that the critical contact angle corresponding to the impregnation of the groove by the drop diminishes with increasing drop volume or decreasing groove size. According to this result, the observed difference in the wetting phenomena between a pyramidal groove and an inverted pyramidal groove can be elucidated.

並列關鍵字

Wetting ； Droplet ； Contact Angle ； Surface Evolver

參考文獻

[1] de Gennes, P. G.; Brochard-Wyart, F.; Quéré, D. Capillarity and Wetting Phenomena, Drops, Bubbles, Pearls, Waves; Springer: New York, 2004.

[2] J. Berthier, Microdrops and digital microfluidics. 2008: William Andrew Publishing.

[5] Wenzel, R. N. Resistance of solid surfaces to wetting by water. Ind. Eng. Chem. 1936, 28, 988-994.

[6] Cassie, A. B. D.; Baxter, S. Wettability of porous surfaces. Trans. Faraday Soc. 1944, 40, 546-551.

[7] Hong, S.-J.; Chang, C.-C.; Chou, T.-H.; Sheng, Y.-J.; Tsao, H.-K. A drop pinned by a designed patch on a tilted superhydrophobic surface: mimicking desert beetle. J. Phys. Chem. C 2012, 116, 26487-26495.

國際替代計量

奈米尺度之液滴-柱與液滴-孔洞系統的潤濕現象

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