高分子液滴於高分子刷表面的潤濕行為

The wetting behavior of polymeric drop on polymer brush surfaces

許家豪(Chia-Hao Hsu)

指導教授 ： 諶玉真

國立臺灣大學/工學院/化學工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201701205

摘要

隨著有機太陽能電池、有機發光二極體等使用導電高分子材料的產業蓬勃發展，研究高分子於基材上的潤濕性質已成為重要課題。將高分子液體置於固態基材上會因為除潤現象而形成球冠形的液滴，此現象會降低高分子薄膜的穩定性。科學家為解決薄膜穩定度問題，對固態基材表面接枝高分子進行表面改質，所形成的結構即為高分子刷。但高分子液體在具有相同化學性的高分子刷上仍然會因為亂度效應而產生自疏性除潤現象。本研究使用耗散粒子動力學模擬方法，模擬液滴及薄膜在固體基材上的除潤現象，接著探討液滴及薄膜在高分子刷上的行為及自疏性除潤現象。

首先，我們模擬液滴的形狀並測量其接觸角，探討高分子鏈段長及親和力對液滴接觸角的影響。接著量測系統不同相態間的表面張力，並以Young’s equation對照理論及模擬的一致性。接著，我們模擬高分子刷，研究液滴在高分子刷上的行為。探討改變液體鏈段長及高分子刷鏈段長對液體接觸角的影響，藉由計算液體的滲透深度了解液體在高分子刷上的潤濕性。我們也改變高分子刷的鏈段硬度，研究高分子刷的鏈段結構是否會影響液體的潤濕性。最後，我們模擬薄膜在固態基材上的除潤現象，並對照實驗上觀察到的薄膜破裂現象及孔洞成長的動態過程，然後模擬薄膜在高分子刷上的破裂並量測孔洞成長速率，了解從液滴觀察到的潤濕性是否和薄膜破裂的孔洞成長速率結論相符。我們也計算孔洞成長速率對時間的關係，並和文獻進行對照，得到相當符合的結果。

關鍵字

耗散粒子動力學 ； 除潤現象 ； 接觸角 ； 表面張力 ； 高分子刷 ； 自疏性除潤現象

並列摘要

The study of the stability of polymeric thin films on solid substrates is of significant importance in many practical applications such as the manufactures of organic solar cells and organic light-emitting diode. However, films on nonwettable substrates tend to exhibit unstable behavior. To resolve this issue, the modification of a nonwettable surface can be accomplished by coating the surface with an appropriate monolayer. Polymer brush is a typical example of applicable candidates. However, an autophobic behavior is observed due to entropic repulsion even if the brushed layer is composed of identical molecules as those forming the films. In this work, dissipative particle dynamics is performed to study the wetting phenomena of polymeric thin films on top of solid substrates or surfaces coated polymer brush.

We start by investigating the effects of polymer length and solid-liquid affinity on the shape and contact angle of a polymeric droplet. The interfacial tensions of solid-liquid, solid-gas and liquid-gas are measured and the Young’s equation is employed to estimate the contact angle. The resulting contact angles are consistent with those obtained directly from simulations verifying that validity of our simulation work. The influences of the molecular lengths of the polymeric films and polymeric brushes on the wetting behaviors of the coated films are examined. It is found that the wettability can be improved by decreasing the molecular lengths of the polymeric films while increasing the lengths of polymer brushes. The stability of a thin film depends on the penetration length of the polymers into the brush layers. Moreover, there exists a critical value of grafting density beyond which the autophobic behavior becomes significant as grafting density increases. The rupture process of a polymer thin film has also been studied. The dewetting velocity increases with increasing grafting density. Our simulation results are consistent with the experimental observation and can be applied to improve adhesion of polymeric thin films on a solid substrate.

並列關鍵字

dissipative particle dynamic ； dewetting phenomenon ； contact angle ； surface tension ； polymer brush ； autophobicity phenomenon

參考文獻

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