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研究生： 黃嘉源
Huang, Jia-Yuan
論文名稱： 三酸甘油酯分子結構對潤滑薄膜之影響
The role of triacylglycerols' structure in thin lubrication films
指導教授： 許文東
Hsu, Wen-Dung
學位類別： 碩士
Master
系所名稱： 工學院 - 材料科學及工程學系
Department of Materials Science and Engineering
論文出版年： 2010
畢業學年度： 98
語文別： 英文
論文頁數： 77
中文關鍵詞： 三酸甘油酯 、潤滑劑 、吸附行為 、奈米侷限
外文關鍵詞： triacylglycerol (TAG), lubricant, adsorption, nanoconfinement
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    • 礦物性潤滑劑價格低廉，卻容易造成環境汙染。三酸甘油酯(triacylglycerols，TAGs)是天然的植物性潤滑劑，具有高黏度、高閃點、低揮發等優點。為了探討三酸甘油酯取代礦物性潤滑劑的可行性，分子動力學 (Molecular Dynamics，MD) 用來研究三酸甘油酯分子的脂肪鏈結構差異所造成的潤滑薄膜特性。研究探討的三酸甘油酯為trilauroylglycerol (LLL-TAG)、tristearoylglycerol (SSS-TAG)、trans-trioleoylglycerol (trans-OOO TAG) 以及trans-trilinolenoylglycerol (trans-LeLeLe-TAG)。前兩個三酸甘油酯為脂肪鏈不同長的飽和分子,後兩個其脂肪鏈分別各有一個及三個不飽和鍵。
    在此研究,首先確認三酸甘油酯的巨觀特性，如密度、相變溫度以及黏性。其次探討奈米尺度下，三酸甘油酯在鑽石基板的表面吸附行為。為了解界面間交互作用的動態過程，研究三酸甘油酯奈米液滴在鑽石基板表面的散佈特性。最後，探討在奈米尺度的侷限下，三酸甘油酯潤滑薄膜所展現的結構特性。
    模擬的結果顯示脂肪鏈的長度及不飽和鍵的個數會影響三酸甘油酯的物理特性。LLL-TAG有較短的脂肪鏈，其核心部分的極性分子團所受到的空間阻礙較小，因而容易彼此團聚。在相變溫度之後，由40個LLL-TAG分子所構成的奈米液滴呈現環狀結構。trans-LeLeLe-TAG分子捲曲的程度較飽和脂肪鏈的TAG分子大，且容易彼此纏繞。當三酸甘油酯靠近鑽石基板表面時，其與基板的交互作用力使其呈現類遞減正弦波的密度分布。隨著鑽石基板大於三酸甘油酯密度，三酸甘油酯逐漸呈現層狀分佈。當三酸甘油酯厚度只有單層分子時，受奈米侷限的SSS and trans-OOO TAGs 展現鑽石基板的依向性。

    Lubricant made by mineral oil is low expense, however, due to the environmental issue; plant-based lubricants attract more and more peoples’ interesting. Triacylglycerols (TAGs) are the major components of naturally occurring oils and fats and are able to produce high strength lubricant films thus become one of candidates to replace mineral-based lubricants.
    In order to assess the ability of TAG molecules to replace mineral-based lubricants, molecular dynamics simulations were performed to investigate the role of triacylglycerols’ structure in thin lubrication films. The selected triacylglycerols are trilauroylglycerol (LLL-TAG), tristearoylglycerol (SSS-TAG), trans-trioleoylglycerol (trans-OOO-TAG), and trans-trilinolenoylglycerol (trans-LeLeLe-TAG). The first two TAGs are saturated molecules with a different number of carbons in the chain, and the second two TAGs are monounsaturated and polyunsaturated molecules, respectively.
    In this study, the bulk properties of TAG bilayers are investigated and then the adsorption between triacylglycerols and diamond substrates are studied. The lubrication properties of triacylglycerol thin films are discussed by confining triacylglycerols between two diamond substrates.
    The simulation results demonstrate that the length of the aliphatic chain and number of unsaturated bond influence the physical properties of triacylglycerols. Due to lower steric hinderance, LLL-TAG demonstrates different spreading characteristics compared to the other TAGs. Trans-LeLeLe-TAG presents a higher degree of recoil and hence a great entanglement between molecules. Close to the diamond surfaces, density of confined TAGs is in form of decreasingly sinusoid-like propagating. The density becomes more localized as the thickness of TAG becomes thinner. Under nanoconfinement, SSS and trans-OOO TAGs demonstrate strong lattice-dependency when their thicknesses are only molecular monolayer at 293 K.

    中文摘要 I Abstract II 誌謝 III Contents IV List of Tables VI List of Figures VII Chapter 1 Motivation 1 Chapter 2 Review 2 2.1. Triacylglycerols 2 2.2. Surface interaction 5 2.3. Nanoconfinement 6 Chapter 3 Molecular dynamics 8 3.1. Molecular dynamics 8 3.2. Leapfrog algorithm 11 3.3. Force field 13 3.4. Potential truncation 18 3.5. Periodic boundary conditions 19 3.6. Ensemble 20 3.7. Coupling methods 21 3.7.1. Temperature coupling 22 3.7.2. Pressure coupling 23 3.8. Efficiency 24 3.8.1. The Verlet neighbor list 24 3.8.2. Linked list (Cell list) and Hybrid list 25 3.9. Parallel 26 3.9.1. Particle Decomposition 26 3.9.2. Domain Decomposition 27 Chapter 4 Simulation method 28 4.1. Selected triacylglycerols 28 4.2. Model of TAG Molecule and Diamond Substrate 29 4.3. Simulation Details 31 4.4. Data analysis method 33 4.4.1. Atomic Density Distribution (ADD) 33 4.4.2. Recoil Length (RL) 34 4.4.3. Surface coverage 35 4.4.4. Bond Orientation Distribution (BOD) 36 Chapter 5 Results and discussion 37 5.1. Adsorption behavior: High TAG density 37 5.1.1. TAG bilayer 37 5.1.2. TAG bilayer on diamond surface: High TAG density 39 5.2. Adsorption behavior: Low TAG density 46 5.2.1. TAG droplet 46 5.2.2. TAG droplet on diamond substrate 49 5.2.3. TAGs on diamond surface: Low TAG density 54 5.3. Nanoconfined TAGs 59 5.3.1. Multilayer 59 5.3.2. Monolayer 62 Chapter 6 Conclusion 74 Reference 75

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