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研究生： 翁韶君
Weng, Shao-Chun
論文名稱： 偶氮染料摻雜於液晶其雷射引致吸附現象之研究
Study of Laser-Induced Adsorption Phenomena of Azo Dye Doped in Liquid Crystal
指導教授： 傅永貴
Fuh, Ying-Guey
共同指導教授: 唐富欽
Tang, Fu-Ching
學位類別： 碩士
Master
系所名稱： 理學院 - 物理學系
Department of Physics
論文出版年： 2014
畢業學年度： 102
語文別： 英文
論文頁數： 98
中文關鍵詞： 液晶 、偶氮染料 、光配向 、吸附 、甲基紅
外文關鍵詞： liquid crystal, azo-dye, photo-alignment, adsorption, methyl red
相關次數： 點閱：172  下載：6 
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    • 本論文主要研究偶氮染料摻雜在液晶中藉由照射雷射光引致吸附於基板造成光配向的現象。偶氮染料（如甲基紅）經雷射光照射後於不同基板上具有不同的吸附效果，基板如素玻璃、表面鍍有銦錫氧化物之導電玻璃、表面鍍有銦錫氧化物之塑膠和表面鍍有阻水氧層之塑膠等。利用座滴法測量各基板之表面能，並利用原子力顯微鏡及化學分析電子能譜儀分析基板表面結構，瞭解不同基板何以具有不同吸附效果。結果顯示基板表面的極性表面能對於吸附效果有顯著的影響，極性表面能愈大，則吸附效果愈好。此外，不同雷射光強度也會影響吸附效果，雷射光強度愈大，則吸附速率愈高，但吸附平整度愈低。因此為了提升基板對於偶氮染料的吸附效果，將各種不同基板預先照射不同強度、不同照射時間的氧電漿，以提升基板的極性表面能並改變基板表面結構，發現可以有效提升偶氮染料的吸附效果，使光配向的良率大幅提升。

    The photo-alignment of liquid crystals by laser-induced adsorption in an azo-dye doped liquid crystal (ADDLC) is studied in this work. The adsorption efficiency of azo-dye (methyl red) in a DDLC cell fabricated using different substrates, such as as-clean glass, ITO coated glass, ITO coated PET and barrier coated PET, differs from one another. The surface energies of different substrates are investigated with sessile drop method. The result shows that surface polarity controls the nucleation and initial growth of methyl red adsorption on different surfaces while the laser intensity is responsible for the time required for complete adsorption. It is found that adsorption rate is proportional to the pumping intensity. Yet, the order of the adsorbed dye decreases with increasing laser intensity. Also, the adsorption rate on various cell substrates in order is glass, ITO PET, ITO glass and finally barrier PET. Furthermore, oxygen plasma is applied for modifying the surface condition of different substrates. The morphology of as-formed methyl red layer on different surfaces is highly influenced by oxygen plasma via the change of surface energy, the polar term especially. Therefore, the performance and efficiency of photo-alignment can be enhanced by oxygen plasma treatment.

    摘要 III Abstract IV 誌謝 VI Table of Contents VII List of Tables X List of Figures XI CHAPTER 1 INTRODUCTION 1 CHAPTER 2 REVIEW OF RELATIVE MATERIALS 4 2.1 Liquid crystals (LCs) 4 2.2 Categories of thermotropic liquid crystals 5 2.2.1 Nematic liquid crystals 5 2.2.2 Cholesteric liquid crystals 6 2.2.3 Smectic liquid crystals 7 2.3 Physical properties of liquid crystals 9 2.3.1 Order parameter 9 2.3.2 Elastic continuum 11 2.3.3 Optical anisotropy 13 2.3.4 Dielectric anisotropy 15 2.4 Dichroic dyes (DDs) 16 2.4.1 Order parameter of dichroic dyes 17 2.4.2 Categories of dichroic dyes 19 CHAPTER 3 REVIEW OF THEORIES RELATIVE TO THE STUDY 21 3.1 Light induced molecular reorientation effect 21 3.1.1 Positive Torque Effect –Jánossy Model 21 3.1.2 Negative Torque Effect – Gibbons Model 24 3.1.3 Photo-isomerization 26 3.2 Jones matrix method 27 3.2.1 Jones matrix of a twisted nematic liquid crystal film 28 3.2.2 Gooch-Tarry condition and Mauguin condition 31 3.3 Surface energy 32 3.3.1 Surface energy and wetting 32 3.3.2 Drop shape measurement method 36 3.3.3 Estimation of surface energy of liquid 37 CHAPTER 4 EXPERIMENTS 39 4.1 Materials 39 4.1.1 Nematic liquid crystal: 5CB 39 4.1.2 Azo-dye: methyl red (MR) 40 4.1.3 Polymer film: Polyvinyl alcohol (PVA) 40 4.2 Sample fabrication 41 4.2.1 Cleaning the substrates 41 4.2.2 Film preparation 43 4.2.3 DDLC mixture preparing 43 4.2.4 Sample assembling 44 4.3 Experimental methods 47 4.3.1 Absorption spectrum of DDLC sample 47 4.3.2 MR adsorption dynamics 48 4.4 Analysis approaches 49 4.4.1 Surface energy measurement 50 4.4.2 Surface configuration 51 4.4.3 Surface material analysis 54 CHAPTER 5 RESULTS AND DISCUSSIONS 57 5.1 Absorption spectra of DDLC 57 5.1.1 Probe beam polarization direction 57 5.1.2 Pump beam exposure duration 58 5.2 Single-side photo-alignment: without plasma treatment 60 5.2.1 MR adsorption dynamics on different substrates 60 5.2.2 MR adsorption dynamics via different pumping intensities 64 5.2.3 Surface energies of different substrates 67 5.2.4 Surface morphologies of different substrates 69 5.3 Single-side photo-alignment: with plasma pretreated substrates 73 5.3.1 MR adsorption dynamics on different substrates 73 5.3.2 MR adsorption dynamics via different pumping intensities 76 5.3.3 MR adsorption dynamics on substrates pretreated with different pumping intensities 80 5.3.4 MR adsorption dynamics on substrates pretreated with different plasma durations 81 5.3.5 Surface energies of different substrates 82 5.3.6 Surface morphologies of different substrates 84 5.4 Comparison of plasma-pretreated and non-treated photo-alignment 87 CHAPTER 6 CONCLUSIONS AND FUTURE WORK 91 6.1 Conclusions 91 6.2 Future work 92 Bibliographies 94

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