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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/64392


    Title: 液橋分離與液面爬升物體之研究;Separation of Liquid Bridge and Meniscus-Climbing Object
    Authors: 張雯音;Chang,Wen-yin
    Contributors: 化學工程與材料工程學系
    Keywords: 液橋;液面爬升;liquid bridge;meniscus-climbing
    Date: 2014-06-09
    Issue Date: 2014-08-11 18:13:37 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 本論文分為兩大部分,分別為液橋分離之研究與液面爬升物體之研究。

    *第一部分:液橋分離之研究
    抗指紋與抗汙機制通常會涉及兩個不同的表面之間形成的液橋,當兩平面在分開時液橋傾向潤濕其中一平面,而使得另一平面表現出抗汙的效果。本論文觀察潤濕特性對液橋被兩相異平面分開的過程之影響,進行實驗與理論模擬的研究。
    在液橋被兩板拉伸至斷裂的過程中,一般而言,在兩平面分開的初期,液橋於兩板上的接觸線皆會撤退,接下來的行為根據兩板間潤濕競爭結果的不同,可分為以下五種模型:(1) 其中一板的接觸線持續後退,另一板的接觸線保持固定不變;(2) 兩板的接觸線皆呈現持續固定的狀態;(3) 其中一板的接觸線保持固定不變,另一板的接觸線於斷裂前開始向外擴張;(4) 其中一板的接觸線持續後退,另一板的接觸線於斷裂前開始向外擴張;(5) 兩平面上的接觸線於斷裂前皆向外擴張。
    實驗結果與Surface Evolver 的模擬結果有很好的一致性,顯然地,在兩板競爭的過程中,潤濕競爭的獲勝方在斷裂前往往伴隨著兩個現象:接觸角上升與接觸線擴張;由模擬分析的結果顯示,潤濕競爭的關鍵取決於兩板的本質接觸角與接觸角遲滯,當兩平板經過壓縮與拉伸的程序後,相較於接觸角較小且接觸角遲滯也較小的平板,兩板中接觸角較大且接觸角遲滯也較大的平板會殘留較多液滴,顯示出潤濕競爭的過程中,接觸角的大小並非唯一決定最終結果之因素,接觸角遲滯亦是相當重要的影響變因。

    *第二部分:液面爬升物體之研究
    自然界一些能在水面上行走的昆蟲,本來是陸生動物,經過進化之後變成能夠適應環境在水上生活,例如水黽,這些小昆蟲大多無法靠自己的足肢爬上岸邊的彎月狀上升水面,於是發展出一種利用表面張力的方法,幫助自己輕易地上岸;藉由固定身體姿勢來使水面變形而產生側向表面張力,這些昆蟲即可獲得一自然的推進力,使自己迅速地滑上岸,此滑行行為即可稱為液面爬升(Meniscus-climbing)。
    本論文旨在深入探討具液面爬升能力的物體之運動行為,藉由改變各種不同的試片材質、形狀與密度,將試片置於懸垂液滴下方,並以高速攝影機觀察其對液面爬升行為的影響。結果顯示,根據試片條件的不同,爬升的情形亦會有顯著的差異。特別的是,具液面爬升能力的試片在爬升之前會先旋轉成垂直方向,接著再爬升至相對應的位置。此外,長度越長的試片能夠爬升的高度越高。具相同面積但形狀不同之試片,因試片長寬比的不同,可發現隨著長寬比增大,試片爬升的高度亦越高。最後,比較不同材質的試片,因密度大小的不同,可觀察到隨著密度越小,試片能爬升的高度也隨之增加。
    ;This study contains two topics: separation of liquid bridge and meniscus -climbing object.

    *PART I: Separation of Liquid Bridge
    Anti-fingerprint or anti-smudge mechanism often involves a liquid bridge formed between two dissimilar surfaces. As the two surfaces are separating, the tendency of the liquid to wet one surface renders the other anti-smudge. In this work, the wetting characteristics of the liquid bridge on two asymmetric surfaces during their separation are investigated both experimentally and theoretically. In general, the contact lines on both surfaces withdraw at the beginning of separation. Before the rupture of the liquid bridge, however, five types of wetting competition are observed: (i) While the contact line remains receding on one surface, it becomes pinned on the other; (ii) The contact line on both surfaces are pinned; (iii) While the contact line is pinned on the one surface, it starts to expand on the other; (iv) While the contact line remains receding on one surface, it start to expand on the other; (v) The contact line on both surfaces are expanded. Our experimental results are in good agreement with the simulation outcomes by Surface Evolver. Evidently, the winning surface is accompanied with the signature of contact angle increment or base diameter expansion before liquid bridge rupture. Further simulation analyses reveal that wetting competition depends on both intrinsic contact angle and contact angle hysteresis. After compression and relaxation of two surfaces, the one with higher contact angle and larger hysteresis may be more wettable than the other with lower contact angle and smaller hysteresis.

    *PART II: Meniscus-Climbing Object
    In nature, some terrestrial insects evolved to live exclusively on the water surface in order to adapt to the environment, such as water striders. They rely on surface tension for static weight support, and use a variety of means to propel themselves along the surface. When these small insects pass from the water surface to land, they have to overcome the slippery meniscus water surfaces that border the water’s edge. They are unable to climb meniscus by using their own legs, therefore developed the meniscus-climbing technique. By fixing their body posture, the water surface is thus deformed to generate lateral surface tension, and then the insects are propelled upon the meniscus surface without moving their legs. This phenomenon is so called “meniscus-climbing”.
    In this study, we investigate the behavior of the objects which have meniscus-climbing ability by testing a variety of materials, shapes and densities of the objects. In experiment, we put these objects below the pendant drop successively, and try to observe the influences caused by these conditions to the meniscus-climbing behavior by the high-speed camera. The result shows that the different conditions of objects make significant difference of climbing situations. Specifically, we observe that the objects with climbing ability rotate themselves into vertical direction just before the climbing behavior. Furthermore, the longer object could climb higher. And in the condition of the same area but different shapes, we find the larger aspect ratio, the higher object climbing. Finally, by comparing different densities of the objects, we observe that the lower density, the higher object climbing.
    Appears in Collections:[化學工程與材料工程研究所] 博碩士論文

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