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標題: | 利用原子力顯微術觀察水和疏水石墨界面的氣體結構 Gas Structures at the Interface between Water and Hydrophobic Graphite Observed by Atomic Force Microscopy |
作者: | Yi-Hsien Lu 呂奕賢 |
指導教授: | 張嘉升(Chia-Seng Chang) |
關鍵字: | 原子力顯微術,疏水,石墨,氣體結構,奈米氣泡,頻率調制模式,峰值輕敲力模式, Atomic Force Microscopy,Hydrophobic,Graphite,Gas Structures,Nanobubbles,Frequency-Modulation Mode,Peak-Force Tapping Mode, |
出版年 : | 2014 |
學位: | 博士 |
摘要: | 氣體的熱力學性質一般主要透由氣體的體相相圖來理解。然而,侷限在奈米空間中的氣體結構觀察卻難以由古典熱力學原理來瞭解。在本篇論文中,我們採用先進的原子力顯微鏡技術研究水和水和疏水性固體界面(高定向裂解石墨)的氣體結構。當水中氣體含量低於飽和溶解度時,在石墨和水的界面我們可觀測到由條狀結構構成的規則層狀結構的成核成長。當水中氣體含量超過飽和溶解度時,我們發現了有序的磊晶層狀結構、無序的薄餅層狀結構和帽型奈米結構;它們的存在以及細微的結構和水中氣體濃度以及氣體種類相關。我們比較了不同成像模式對這些氣體結構的觀察,包含頻率調制、振幅調制和峰值力輕敲模式。頻率調制可獲得最正確的表面形貌訊息,而峰值力輕敲模式可探測較底層的結構。我們也探討這些界面結構的力學特性和它們的物理本質。從這些觀察中,我們認為疏水性固體表面對水中溶解的氣體分子提供了一個低化學勢能的吸附位置;而這些界面氣體結構可藉由界面水進一步穩定。在室溫的環境下,當氣體分子被限縮在一個足夠小的空間中,它們可以聚集成為凝態結構;而在這樣的狀況下,氣體的熱力學性質主要是根據界面的交互作用所決定的。在結晶性的固體表面,這樣的氣體甚至可能成為固態結構。 The thermodynamic properties of gases have generally been understood primarily thorough phase diagrams of bulk gases. However, observations of gases confined in a nanometer space have posed a great challenge to understand using classical thermodynamics. In this thesis, we investigated interfacial gas structures between water and a hydrophobic solid surface, highly ordered pyrolitic graphite, by using advanced atomic force microscopy techniques. Nucleation and growth of bright patches at the graphite-water interface was observed when the gas concentration was below the saturation level. The bright patches, suspected to be caused by adsorption of N2 molecules at the graphite-water interface, were composed of domains of an ordered row-like structure. When the gas concentration was above the saturation level, ordered epitaxial layer(s), disordered pancake-shaped layers and cap-shaped nanostructures were observed; their existence and detailed structures could be dependent on the concentration and type of gas in water. Comparison of different imaging modes, including the frequency-modulation, the amplitude-modulation, and the PeakForce tapping techniques, on the interfacial gas structures were performed. We demonstrate that the frequency-modulation mode can yield the most accurate topographic information while the Peak-Force tapping mode are able to determine the underlying structures. Mechanical properties and physical essences of these interfacial structures are also discussed. We propose that hydrophobic solid surfaces provide low-chemical-potentials sites at which gas molecules dissolved in water can be adsorbed. The structures are probably further stabilized by interfacial water. Gas molecules can agglomerate into a condensed form when confined in a sufficiently small space under ambient conditions. The ordering and thermodynamics properties of the confined gases are determined primarily according to interfacial interactions. The crystalline solid surface may even induce a solid-gas state. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/56664 |
全文授權: | 有償授權 |
顯示於系所單位: | 物理學系 |
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