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系統識別號 U0026-1012201401440600
論文名稱(中文) 聚乙烯基咔唑薄膜式液晶元件之光學與光電特性研究
論文名稱(英文) Studies of optical and electro-optical properties of poly(N-vinylcarbazole) film based liquid crystal devices
校院名稱 成功大學
系所名稱(中) 光電科學與工程學系
系所名稱(英) Department of Photonics
學年度 103
學期 1
出版年 103
研究生(中文) 劉彥岑
研究生(英文) Yen-Chen Liu
學號 L78991102
學位類別 博士
語文別 英文
論文頁數 104頁
口試委員 指導教授-傅永貴
召集委員-蔡錦俊
口試委員-李偉
口試委員-郭啟東
口試委員-許家榮
中文關鍵字 液晶  聚乙烯基咔唑  相分離  分子同分異構反應 
英文關鍵字 liquid crystals  poly(N-vinylcarbazole)  phase separation  isomerization 
學科別分類
中文摘要 本論文研究了偶氮苯材料的光及電同分異構化效應,及利用該光、電調控機制建構聚乙烯基咔唑薄膜式液晶光調控器。反式同分異構物經由光致同分異構化效應轉換為順式同分異構物,並使偶氮苯液晶自身等溫相變成各向同性態,此亦導致聚乙烯基咔唑溶解於液晶中。而液晶和聚乙烯基咔唑之相分離,則可經由快速之電、光致異構化反應或緩慢暗回復效應而引致的反向相變過程而產生。在快速之相分離反應中,聚乙烯基咔唑會吸附在樣品表面產生枝條狀結構及微米尺寸的液晶區域,形成穩定的光散射態。相反,經由慢速之暗回復過程,將生成平坦均一化的聚乙烯基咔唑表面,並且在樣品上提供了穩定穿透態。論文中亦針對順式異構物在穩定直流電壓下的濃度變化進行詳細量測與討論。而經由上述各條件所形成之聚乙烯基咔唑薄膜皆使用掃描式電子顯微鏡進行觀察與檢驗。
不同相分離機制定義了在基板表面所重建之不同聚乙烯基咔唑薄膜結構,並應用於可調式液晶光閥。光閥之穿透(散射)態,可利用緩慢(快速)之偶氮苯液晶及聚乙烯基咔唑之相分離,而產生平坦(粗糙)的聚乙烯基咔唑薄膜結構而達成。粗糙的聚乙烯基咔唑薄膜使介面液晶層形成多個微米大小的區域,而達到超性能之散射。平坦的聚乙烯基咔唑薄膜則使光閥呈現優良之穿透態,這個穿透及散射間切換可反覆的進行。此利用偶氮苯液晶及聚乙烯基咔唑製成之高散射式光調控器,其具有高對比度(370:1)。
英文摘要 This thesis investigates the photo- and electro-isomerization effects on azobenzene material and demonstrates the optically and electrically controllable liquid crystal (LC) light modulator based on the poly(N-vinylcarbazole) (PVK)-coated liquid crystal (LC) cells. The isothermal phase transition from LC to isotropic states induced by the photo-isomerization of azobenzene LCs (azo-LCs) from trans- to cis-isomers results in the dissolution of PVK into azo-LCs. The phase separation of PVK and LCs occurs by reversing phase transition through rapid electro-, photo-isomerization or slow dark-relaxation. PVK molecules are adsorbed onto the cell substrates forming branch-like PVK structures, and generates micron-sized LC domains during rapid phase separation to develop stable light scattering. However, a uniform PVK film is obtained on the surface during the slow dark-relaxation, producing stable transparency. This thesis discusses in details the variations of the population of cis-isomers as functions of amplitude of the applied DC voltage. The PVK films are examined in details using the scanning electron microscopy (SEM).
The proposed phase separation process determines the reformed PVK films on the substrates to obtain switchable LC light valves. Transparent (scattering) states can be demonstrated using uniform (rough) morphologies of PVK generated by slow (rapid) phase separation of PVK and azo-LCs from cis- to trans-isomers. Good scattering performances resulting from rough PVK surface induces micron-sized LC domains and the transparent performance resulting from the reformed uniform PVK surface can be reversibly switched. Finally, the contrast ratio of the highly efficient scattering mode light modulators based on azo-LCs and PVK films is measured to be about 370.
論文目次 摘要……………………I
Abstract……………………III
Acknowledgement……………………V
Contents……………………VI
List of tables……………………IX
List of figures……………………X

Chapter 1 Introduction……………………1
1.1 Preface……………………1
1.2 Liquid crystals……………………2
1.2.1 History of liquid crystals……………………2
1.2.2 Category of liquid crystals……………………3
1.2.3 Physics of nematic liquid crystals……………………8
1.3 Polymer dispersed liquid crystal (PDLC)……………………15
1.4 Azobenzene materials……………………17
1.4.1 Photo- and electro-isomerization……………………18

Chapter 2 Device relating theory……………………22
2.1 Organic polymers-Poly(N-vinylcarbazole)……………………22
2.1.1 Liquid crystal alignment based on the PVK film………………23
2.1.2 Relaxation and thermodynamics in polymers……………………23
2.1.3 Photoconductivity of the poly(N-vinylcarbazole)…………26
2.2 The scattering mode LC light shutters……………………27
2.2.1 Solvent-induced phase separation……………………28
2.2.2 Thermally induced phase separation……………………29
2.2.3 Polymerization induced phase separation……………………32
2.2.4 Particular thermally induced phase separation of liquid crystal and poly(N-vinylcarbazole) films……………………33

Chapter 3 Experiment preparations……………………36
3.1 Materials used……………………36
3.1.1 Liquid crystals……………………36
3.1.2 Organic polymer……………………37
3.1.3 Monomer……………………38
3.1.4 Azobenzene material……………………39
3.2 Fabrications of samples……………………40
3.3 Analyzing tools……………………42
3.3.1 Polarized optical microscope (POM)……………………43
3.3.2 Scanning electron microscope (SEM)……………………44
3.3.3 Temperature controller……………………46
3.3.4 Thermal imager……………………47

Chapter 4 Photo-isomerization-induced LC scattering based on the poly(N-vinylcarbazole) films……………………49
4.1 All-optically controllable scattering mode light modulator based on azobenzene liquid crystals and poly(N-vinylcarbazole) films……………………49
4.1.1 Introduction……………………50
4.1.2 Experiments and device properties……………………52
4.1.3 Results and discussions……………………53
4.2 Conclusions……………………65

Chapter 5 Electro-isomerization of the azobenzene liquid crystal and their application in LC-scattering device……………………67
5.1 Photo- and electro-isomerization of azobenzenes based on polymer-dispersed liquid crystals doped with azobenzenes and their applications……………………68
5.1.1 Introduction……………………68
5.1.2 Experiments and device properties……………………71
5.1.3 Results and discussions……………………72
5.2 Isothermal electrically and optically induced phase separation of liquid crystal and poly(N-vinylcarbazole) films……………………81
5.2.1 Introduction……………………81
5.2.2 Experiments and device properties……………………83
5.2.3 Results and discussions……………………84
5.3 Conclusions……………………92

Chapter 6 Conclusions and future works……………………94
6.1 Conclusions……………………94
6.2 Future works……………………96

References……………………97
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