奈米尺度下界面活性劑的吸附與聚集之強烈競爭關係;Strong Competition between Adsorption and Aggregation of Surfactant in Nanoscale Systems

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题名:	奈米尺度下界面活性劑的吸附與聚集之強烈競爭關係;Strong Competition between Adsorption and Aggregation of Surfactant in Nanoscale Systems
作者:	黃柏榕;Huang, Po-Jung
贡献者:	化學工程與材料工程學系
关键词:	界面活性劑;奈米尺度;吸附;微胞化;surfactant;nanoscale;adsorption;micellization
日期:	2019-06-21
上传时间:	2019-09-03 12:28:01 (UTC+8)
出版者:	國立中央大學
摘要:	當兩種物質相分離所形成的分界，我們稱其為界面，而界面活性劑即為一種可改變界面性質的化合物。本研究利用多體耗散粒子動力學法，探討奈米尺度下界面活性劑的界面吸附與液相聚集之強烈競爭關係，並分別從液氣相、固液相、固液氣三相探討其影響程度。在液氣相情況下，於奈米液膜其表面張力、表面密度和臨界微胞濃度皆受到尺度所影響。隨著濃度的增加，即使已超過臨界微胞濃度，表面密度依舊持續上升。唯有當其體濃度超過臨界微胞濃度數十倍才有機會使表面達飽和。在模擬系統可以清楚的看到有吸附於液氣界面的表面微胞和存在於副層的界面活性劑。前者可減少界面活性劑疏水尾端與液體粒子的接觸，後者的界面活性劑濃度則明顯高於液相內界面活性劑濃度。奈米尺度下界面活性劑的強烈的交互作用(吸附行為與微胞化)可歸因於在宏觀系統下有相對大的表體比；事實上，可將此交互作用描述為界面活性劑在液相內和界面上數量的比例關係，其比值總小於1在奈米尺度下。接著，於固液相情形下，改變界面活性劑性質將對結果造成不同的影響；由於疏水尾端粒子與親水頭基粒子數量上的差距，使得結果有所不同。最後，於固液氣三相，不論界面活性劑的性質改變，液氣界面皆為其偏好分佈的首選目標，固液界面與液相的競爭關係則決定於其性質變化。 ;The Interface is the boundary of two incompatible material, and surfactant can change the property of interface. Strong competition between interface adsorption and bulk aggregation of surfactant in nanoscale systems was explored by Many-body Dissipative Particle Dynamics simulations. Moreover, the interface adsorption and bulk aggregation in nanoscale systems are investigated in liquid/vapor, solid/liquid and solid/liquid/vapor phases. First of all, in the system of liquid/vapor phases, the size-dependent behavior including surface tension (, surface density (, and critical micelle concentration (CMC) was illustrated by considering a nanofilm with the thickness L. It is found that in nanoscale systems as the surfactant concentration increases,  continues rising even after CMC is exceeded. The saturation level of  is achieved only when the surfactant bulk concentration is over ten times of CMC. Moreover, both surface micelles formed by adsorbed surfactant and the sublayer below the adsorbed layer are clearly identified. The former can reduce the contacts of adsorbed surfactant with water, while the latter has the surfactant concentration significantly higher than that in bulk. The strong coupling between adsorption and micellization is attributed to large surface-to-volume ratio compared to macroscopic systems, and can be simply realized by the fact that the ratio of the numbers of surfactant distributed in bulk (nbulk) and at interface (nads) is always less than unity (nbulk/nads < 1) in nanoscale systems. Besides, in the system of solid/liquid phases, the change of surfactant property would make significantly different results. Due to the majority of amount, the hydrophobic tail plays a more important role over the hydrophilic head. Nevertheless, despite the variation of the surfactant property in the system of solid/liquid/vapor phases, the liquid-vapor interface is always the priority for the surfactant to stay. However, the preference of the solid-liquid interface and bulk for surfactant would depend on its property.
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