氏名　JAIS BIN LIAS
学位の種類　博士（工学）
学位記番号　博甲第597号
学位授与の日付　平成23年8月31日
学位論文題目　Study on Application of UV-Processed Molecular Alignment in Liquid Crystal Devices　（液晶素子におけるUV処理された分子配向の応用に関する研究）

論文審査委員
　主査　准教授　木村　宗弘
　副査　教授　小野　浩司
　副査　准教授　塩田　達俊
　副査　准教授　河原　成元
　副査　本学名誉教授　赤羽　正志

• 論文目次
• 論文要旨
• 論文審査の結果の要旨

［平成23（2011）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

　page
Chapter1　p.1
Introduction　p.1
　1.1　History of Liquid Crystals　p.1
　1.2　Research Background　p.3
　1.3　Objectives of the Investigation　p.5
　1.4　Outline of This Thesis　p.6

Chapter2　p.8
Physical Properties of Liquid Crystals　p.8
　2.1　Introduction　p.8
　2.2　Thermotropic,Polymeric and Lyotropic Liquid Crystals　p.9
　2.2.1　Thermotropic Liquid Crystal　p.9
　2.2.1.1　Nematic and Cholesteric Phases　p.10
　2.2.1.2　Smetic A and Smetic C Phases　p.12
　2.2.2　Polymer Liquid Crystal　p.12
　2.3　Properties of Liquid Crystals　p.13
　2.3.1　Dielectric Constant　p.13
　2.3.2　Refractive Index　p.14
　2.3.3　Elastic Constants　p.14
　2.3.4　Viscosity　p.16

Chapter3　p.19
Optics of Liquid Crystals　p.19
　3.1　Introduction　p.19
　3.2　Light propagation in an Isotropic Medium　p.19
　3.3　Light propagation in an Anisotropic Medium　p.22
　3.4　Jones Matrix　p.26
　3.5　4x4 Matix Method　p.29
　3.6　Light transmissoin and reflection by an anisotropic plate sandwiched between isotropic media　p.35

Chapter4　p.40
Bistable Liquid Crystal Technologies　p.40
　4.1　Introduction　p.40
　4.2　Principles of Operation, Advantages and Limitations　p.40
　4.2.1　Bistable Cholesteric Display　p.40
　4.2.2　Surface Stabilized Ferroelectric Liquid Crystal （SSFLC） Display　p.41
　4.2.3　Bulk Bistable Twisted Nematic （360°BTN） Display　p.42
　4.2.4　Surface Nematic Bistability　p.43
　4.2.4.1　Zenithal Bistable Display （ZBD）　p.44
　4.2.4.2　Surface Controlled BistableNematic （BiNem） Display　p.45
　4.3　Present State and Expected Future of Bistable LC Technologies　p.46

Chapter5　p.49
Liquid Crystalline Blue Phases　p.49

Chapter6　p.58
Investigation of Liquid Crystal Alignment on Patterned-Alignment Films Processed by UV Light　p.58
　6.1　Introduction　p.58
　6.2　Liquid Crystals Alignment Method　p.60
　6.2.1　Rubing Method　p.60
　6.2.1.1　Definition　p.60
　6.2.2　Photoalignment Method　p.62
　6.3　Bistable Switching Models　p.63
　6.4　Experiment　p.64
　6.4.1　Orientation Confirmation of the Twisted-Homogeneous Bistable and Bistable HAN Cells　p.65
　6.4.2　Measurement of the Twisted Angle on the Twisted-Homogeneous Bistable Cell　p.66
　6.4.3　Measurement of the Pretilt of the Twisted-Homogeneous Bistable Cells　p.67
　6.4.4　Switching Experiment of the Twisted-Homogeneous Bistable Cell　p.68
　6.5　Result and Discussion　p.68
　6.5.1　Orientation Confirmation of the Twisted-Homogeneous Bistable and bistable HAN Cells　p.68
　6.5.2　Measurement of the Twisted Angle on the Twisted-Homogeneous Bistable Cell　p.70
　6.5.3　Measurement of the Pretilt of the Twisted-Homogeneous Bistable Cell　p.71
　6.5.4　Switching Experiment of the Twisted-Homogeneous Bistable Cell　p.72
　6.5.5　Effect of the Pattern Pitch　p.74
　6.6　Conclusion　p.75

Chapter7　p.78
Determination of Polar Anchoring Strength for Polymer-Stabilized Blue Phase Liquid Crystal Devices Processed by UV Light-SOITE Method　p.78
　7.1　Introduction　p.78
　7.2　Experimental Methods　p.79
　7.2.1　Observation of Polymer-Stabilizied Blue Phase　p.79
　7.2.2　Measurement of Poler Anchoring Energy Coefficient Aθby SOITE Method　p.80
　7.3　Result and Discussion　p.83
　7.3.1　Observation of Polymer-Stabilizied Blue Phase　p.83
　7.3.2　Measurement of Poler Anchoring Energy Coefficient Aθby SOITE Method　p.84
　7.4　Conclusion　p.87

Chapter 8　p.89
Determination of Polar Anchoring Strength for Polymer-Stabilized Blue Phase Liquid Crystal Devices Processed by UV Light-Hung' Method　p.89
　8.1　Introduction　p.89
　8.2　Experimental Method　p.90
　8.2.1　Observation of Polymer-Stabilized Blue Phase　p.90
　8.2.2　Measurement of Refractive Indices and Splay Elastic Constants, K11 aand Bend Elastic Constant, K33　p.92
　8.2.3　Measurement of Polar Anchoring Strength Wd by Hung's Method, K11 and Bend Elastic Constant, K33　p.93
　8.3　Result and Discussion　p.99
　8.4　Conclusion　p.103

Chapter 9　p.106
Conclusion　p.106

Publication and Research Activitives　p.108

Acknowledgement　p.110

　Photoalignment technique in liquid crystal devices （LCDs） fabrication processes is classified into a non-contact process which provides an anisotropy in liquid crystal （LC） alignment layer by exposing ultra violet （UV） light. The greatest benefit for using this technique is to avoid electrostatic charges and impurities on the substrate. Moreover, photoalignment can realize the structures which has the required liquid crystal director azimuth with the selected area of the cell, thus viewing angle characteristics can be improved by the pixel dividing. In this study, the photoalignment technique was applied to the fabrication of a bistable type LCD and polymer-stabilized blue phase （PSBP） LCD.
Most liquid crystal devices are monostable, which possesses only one possible state in absence of field. They requires continuous voltage application and frequent image refreshment, which is the cause of the energy consumption and limits the multiplexability. In other word, monostable devices have no intrinsic pixel memory and they need an active matrix or other external storage elements to obtain high multiplexing levels. Bistable type LCD have two （or more） stable states. Once an image displayed, the director state in each pixels is memorized for a long time, ranging from seconds up to years, until when the new image is overwritten. This intrinsic memory capability is a peculiar advantage of the bistable type LCD, provides a potential to reduce the power consumption, especially for the specific application which is unnecessary frequent update. In this study, to fabricate a bistable LCD （BLCD） by using unpolarized UV light irradiation, single-step laser patterning to photoalignment layer was proposed. Bistability can be achieved by two equilibrium configurations of LC director profile which is induced by a periodically patterned alignment layer on a substrate. The patterns were formed by stripes of alternating random planar and homeotropic anchoring in the order of 0.5 μm. In this work, two possible configurations of bistable LCD that can be obtained by combining a micropatterned surface formed with alternating random-planar- and homeotropic-alignment with planar- or homeotropic-alignment surfaces were proposed. The alignment properties of the two proposed BLCD models such as twisted angle, pretilt angle and its microscopic switching behavior and memory effect were investigated and determined. It was assumed that the formation of the two bulk orientational states will depend on the degree of depolarization of the laser light, the stripe periodicity and the effective anchoring strength of the patterned surface.
Recently, blue phase （BP） liquid crystal （LC） has attracted the attention of many researchers because of its exotic structures and properties. BP with a structure of self-assembled three-dimensional cubic structure formed by double-twisted arranged LC cylinders is usually observed in a cooling process from isotropic to chiral nematic （N*） phase LC. Such a molecular arrangement exhibits an optical isotropy, selective reflection to circular polarized light, a reflective band switched by external fields, and microsecond response. These characteristics show some potential applications of BP such as large-screen flat panel displays and tuneable photonic band gap devices.
　The very narrow stable temperature range of the BP, however, typically a few Kelvin, is a serious problem for device applications. Although, much effort has been made to expand the narrow temperature range of the BP, Kikuchi et al. firstly reported that the temperature range of the BP can be expanded over 60 ℃ by adding a small quantity of precursor polymers within the BP materials, referred to as a polymer-stabilized blue phase （PSBP）.
To realize a fast response LCD, PSBP LCD was successfully fabricated by applying the UV photoalignment technique to expand the temperature range of blue phase （BP）. As a coupling coefficient, the polar anchoring strength between the BP LC and the diacrylate type polymer was evaluated by means of the oblique incidence transmission spectroscopic ellipsometry using two methods which are SOITE method and Hung's method. In the two methods, different type of LC materials and chiral dopant were employed. As a result, the polar anchoring strength measured with SOITE and Hung's methods were determined in the order of 10-4J/m2. The polar anchoring strength also compared with the other materials which was used for polymer dispersed LCD. We found that the host BPLC materials and the diacrylate-type polymer in a PSBP LC having vertical （homeotropic） alignment. It is assumed that the strong polar anchoring strength between the BPLC and the diacrylate-type polymer allows the PSBP LC to maintain and stabilize its structure. Thus, the BP temperature range can be broadened by adopting a diacrylate-type polymer into host BPLC materials.
　The finding that the polar anchoring strength is relatively high offers an important insight with which to understand and optimize the polymer stabilization of BP.

　本論文は、「Study on Application of UV-Processed Molecular Alignment in Liquid Crystal Devices」と題し、9章より構成されている。
　第1章「Introduction」では、液晶に関する研究の歴史、液晶ディスプレイ（LCD）の特徴などについて述べている。これらの背景をふまえ、本論文の研究目的と範囲を述べている。
　第2章「Physical Properties of Liquid Crystals」では、液晶相の特徴、液晶の重要な物性定数である誘電率異方性、弾性定数異方性、粘性係数異方性についてまとめている。
第3章「Optics of Liquid Crystals」では、LCDの光学解析についてマクスウェル方程式から出発し、ベレマンの4×4行列法による透嘩率および反射率の導出について詳述している。
　第4章「Bistable Liquid Crystal Technologies」では、双安定型液晶素子の利点を述べ、これまでに研究されてきたコレステリック液晶・表面安定化強誘電性液晶、ネマティック液晶を用いたバルク双安定型および界面双安定型液晶素子を概観し、それぞれの特徴や問題点を総括している。
　第5章「Liquid Crystalline Blue Phases」では、その高速応答性から次世代ディスプレイとして期待されているブルー相液晶について、研究の歴史やブルー相出現温度範囲の拡張技術としての高分子安定化について概説している。
　第6章「Investigation of Liquid Crystal Alignment on Patterned-Alignment Films Processes by UV Light」では、UV光配向法による双安定型液晶表示素子の作製技術について詳述している。垂直配向性ポリイミド膜にストライプ状フォトマスクを介して非偏光UV光を照射することによってポリイミド膜近傍における双安定な分子配向を実現できることを明らかにし、分子配向捻じれ角およびメモリー性について評価を行った。
　第7章「Determination of Polar Anchoring Strength for Polymer-Stabilized Blue Phase Liquid Crystal Devices Processed by UV Light-SOITE Method」では、高分子安定化ブルー相（PSBP）LCDにおいてブルー相を安定化させる高分子とネマティック液晶の間の配向状態は垂直配向であることを明らかにした。続いて、高分子の応答特性を最適化するためのデバイスパラメータとして、高分子と液晶の間の極角アンカリングエネルギーに着目し、対称斜入射透過偏光解析法による高分子とネマティック液晶の間の水平配向極角アンカリングエネルギーが10^4 J/m2オーダーであることを見出した。
　第8章「Determination of Polar Anchoring Strength for Polymer?Stabilized Blue Phase Liquid Crystal Devices Processed by UV Light-Hung′s Method」では、ハイブリッド配向LCDを用いた透過偏光解析法によってPSBPにおける高分子とブルー相液晶との間の垂直配向極角アンカリングエネルギーが10^4 J/m2オーダーであることを見出した。
　第9章「Conclusions」では、本研究で得た結果を総括している。
　以上のように本論文では、実用的な観点からUV配向処理のLCD作製への応用について有用な知見を与えている。よって、本論文は工学上及び工業上貢献するところが大きく、博士（工学）の学位論文として十分な価値を有するものと認める。