氏名　Thet Naing Oo
学位の種類　博士（工学）
学位記番号　博甲第436号
学位授与の日付　平成19年8月31日
学位論文題目　Study of Alignment of Nematic Liquid Crystals at Patterned Surfaces　（パターン表面におけるネマティック液晶の配向に関する研究）
論文審査委員
　主査　教授　赤羽　正志
　副査　教授　小野　沽司
　副査　准教授　安井　寛治
　副査　准教授　河合　晃
　副査　准教授　木村　完弘

• 論文目次
• 論文要旨
• 論文審査の結果の要旨

［平成19（2007）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

Chapter 1.　Introduction　p.1
　1.1　Historical Perspective of Liquid Crystals　p.1
　1.2　Overview of Alignment of Liquid Crystals　p.3
　1.3　Objectives　p.7
　1.4　Outline of this thesis　p.7
Chapter 2.　Physical Properties and Optics of Liquid Crystals　p.11
　2.1　Molecular Structure and Chemical Compositions　p.11
　2.2　Lyotropic, polymeric, and Thermotropic Liquid Crystals　p.13
　2.2.1　Lyotropic Liquid Crystals　p.13
　2.2.2　Polymeric Liquid Crystals　p.13
　2.2.3　Thermotropic Liquid Crystals　p.14
　2.3　Physical Properties of Liquid Crystalline Materials　p.18
　2.3.1　Anisotropy　p.18
　2.3.2　The Magnetic Susceptibility　p.19
　2.3.3　Refrative Indices　p.20
　2.3.4　Dielectric Constants　p.22
　2.3.5　The Frank-Oseen Elastic Energy　p.26
　2.3.6　Elastic Constants　p.27
　2.3.7　Viscosity　p.30
　2.4　Optics of Liquid Crystals　p.31
　2.4.1　Light propagation in an isotropic medium　p.32
　2.4.2　Light propagation in an anisotropic medium　p.34
　2.4.3　Jones matrix　p.38
　2.4.4　4×4 matrix method　p.41
　2.4.5　Light transmission and reflection bye an anisotropic plate sandwiched between isotropic media　p.47
Chapter 3.　Surface Phenomena and Alignment of Liquid Crystals　p.54
　3.1　Introduction　p.54
　3.2　Surface Energy　p.55
　3.2.1　Wetting of Solid Substrate　p.55
　3.2.2　Orientation by interface__Anchoring　p.57
　3.2.3　Surface Energy and Anchorage of a Nematic Liquid Crystal　p.58
　3.3　Alignment Mechanism of Nematic Liquid Crystals　p.60
　3.3.1　Surface Tension and the Director Orientation in Nematics　p.60
　3.3.2　Liquid Crystal Orientation　p.63
Chapter 4.　Investigation of Surface Alignment of Liquid Crystal Multilayers Evaporated Patterned Polyvinylcinnamate Film　p.72
　4.1　Introduction　p.72
　4.2　Concept of the three-dimensional suface profiler　p.76
　4.3　Experiment　p.78
　4.4　Result nad Discussion　p.79
　4.5　Cobclusions　p.85
Chapter 5.　Investigation of Surface Alignment of Liquid Crystal Multilayers Evaporated Patterned Polyimide Film　p.89
　5.1　Introduction　p.89
　5.2　Experiment　p.90
　5.3　Results and Discussion　p.92
　5.4　Conclusions　p.97
Chapter 6.　Investigation of Surface Alignment of Liquid Crystal at Micropatterned Polyyimide Surface: Exposure Type I　p.100
　6.1　Introduction　p.100
　6.2　Finite Element Method　p.102
　6.2.1　Element charateristics and displacement functions　p.102
　6.2.2　Applying Finite Element modeling to exposure type I　p.106
　6.2.3　Calculation model　p.108
　6.2.4　Effect of elastic constant ratio k33/k11 and the stripe width area ratio　p.110
　6.3　Experment, Results and Discussion　p.116
　6.3.1　Alignment direction of liquid crystal on photo-treated PI-VA surface　p.116
　6.3.2　Surface Patterning　p.117
　6.3.3　Measurement of anchoring energies and pretilt angles　p.118
　6.3.4　Switching consideration of a micropatterned liquid crystal cell　p.131
　6.4　Conclusions　p.139
Chapter 7.　Microscopic Investigation of Memory Effect found in Micropatterned Nematic Liquid Crystal Cells　p.143
Reference　p.86

The alignment of liquid crystals （LCs） induced by surfaces is interesting both from fundamental and technological points of view. The substrate-induced alignment of LCs is essential for the understanding of substrate-LC interactions and the design and fabrication of new LC display devices. Most past studies on the substrate aligning effect have been focused on the uniform treatment of the substrate surfaces. Recently, textured inhomogeneous surfaces （on scales of the order of 100 μm down to ?100 nm） have been designed for the patterned alignment of LCs. The patterned alignment technique generates different surface alignment orientations on a micro- or nanometer length-scale. The patterned alignment technique also provides unique control of the LC orientation both near the alignment surface and in the bulk of the LC layer. Moreover, the surface patterning also facilitates to reveal a clear picture of different alignment mechanisms/states at the same substrate surface. In this study, alignment of nematic LCs at patterned surfaces has been investigated to explore new alignment mechanisms or orientational states and to achieve novel functions such as bistability and multistability. The main objective of this work is to investigate alignment of nematic liquid crystals at patterned surfaces designed through an approach using photomask technique and a photoalignment layer. The photomask technique enables discontinuously varying periodic boundary conditions. In this work, we proposed a single-step ultra-violet light or laser patterning on a photoalignment layer using a photomask technique. Surface patterning was done in two ways: large scale patterning （on length scale of 100 μm） and sub-micron scale patterning （on length scale of 0.5 μm）.
With regard to the large scale patterning, the surface alignment of LC multilayers evaporated on periodically patterned substrate surface was visualized by means of a three-dimensional surface profiler. It was observed that the photoinduced anisotropy of periodically patterned photoalignment film can be visualized as a topographically different LC multilayers. The surface alignment of liquid crystal multilayers evaporated on two different practically used photoalignment films （polyvinylcinnamate and polyimide） has been demonstrated for the first time by means of the novel surface profiler, opening a new area of research in surface alignment of liquid crystals. From the practical viewpoint, the open air molecular deposition on photo-patterned alignment film can be a potential technique to realize a functional surface. As a molding technique, the basic concept is quite unique compared with the printing technique because the open air molecular deposition can be looked upon as a non-contact molding technique. For visualization purpose, polarized microscopy cannot provide vertical information without combining another analysis. The strong point of the surface profiler is that a nano-scale vertical profile with millimeter range can be measured. It is also remarkable that the surface profiler is applicable not only to the hard material but also to the soft material such as gel and liquid crystal due to its non-contact measurement procedure and thus our research shows that this technique turns out to be a useful technique in its own way.
In regard to a sub-micron scale patterning, firstly a two-dimensional finite element method （FEM） was used to analyze nematic LC alignment on a micropatterned surface. The patterns were formed by stripes of alternating planar and homeotropic anchorings. There are two types of exposure patterns where the preferred azimuthal alignment on the planar stripes is either perpendicular （exposure type I） or parallel （exposure type II） to the stripes. To realize these surfaces and verify FEM simulation experimentally, micropatterned surfaces were fabricated using a photomask with 0.5 μm Line and Space, in order to obtain a period of 1 μm since the characteristic length scale of the surface pattern should be in the mesoscopic （nanoscopic） regime between the molecular and the optical length scales. From both theoretical and experimental results, it was found that important controlling parameters are length scale of the pattern, elastic constants of LC materials used and stripe width area ratio between different/competing surface potential areas to achieve uniform LC alignment via non-uniform surface alignment potentials. From experimental results, it was also found that the area ratios of two equilibrium states depend on LC materials used, cell history, cell configuration and other physical parameters such as polar and azimuthal anchoring strengths.
Several kinds of memory effects in LC cells have been reported and widely discussed thus far. They are interesting from the viewpoint of fundamental research as well as for improving the quality of existing LC display devices. These memory effects can be generally classified into two groups. The first group is concerned with surface memory effects （SME） without applying external fields. The second group is concerned with memory effects under the influence of applied external fields. This type of memory effect maintains the field-induced orientation of LCs caused by external fields after the field is removed. In this thesis, we demonstrate two kinds of memory effects by using a micropatterned surface. The purpose of this investigation is to examine memory alignment of nematic LCs on isotropic, untreated indium-tin-oxide （ITO） substrates by imprinting a counter-alignment i.e. a micropatterned alignment on the ITO surface with the help of a temperature gradient effect. We also studied switching behavior of this memory-induced LC cell. It was confirmed that we succeeded in imprinting a high tilt on the ITO substrate and the imprinted pretilt angle on the ITO substrate was lower than that on the counter-micropatterned substrate.

　本論文は、「Study of Alignment of Nematic Liquid Crystals at Patterned Surfaces（パターン表面におけるネマティック液晶の配向に関する研究）」と題し、異種配向処理を周期的に施したパターン表面における液晶配向を研究したもので、9章より構成されている。
　第1章「Introduction」では、本研究の背景および研究目的と意義について述べている。
　第2章「Physical Properties and Optics of Liquid Crystals」では、液晶の物性、特に本研究に密接に関係しているネマティック液晶の弾性理論と光学特性について概説している。
　第3章「Surface Phenomena and Alignment of Liquid Crystals」では、液晶デバイスにおいて最も重要なプロセスである基板の表面配向処理法について述べ、液晶の表面配向メカニズムについて述べている。
　第4章「Investigation of Surface Alignment of Liquid Crystal MultilayersEvaporated on Patterned Polyvinylcinnamate Films」、第5章「Investigation of Surface Alignment of Liquid Crystal Multilayers Evaporated on Patterned Polyimide Films」では、325nmHe-Cdレーザ光を100μm line and space のフォトマスクを通して、それぞれ、Polyvinylcinnamate、垂直配向用Polyimidを塗布した基板に照射して作成したパターン表面における液晶配向を3次元サーフェスプロファイラーで初めて観測している。その結果を、偏光顕微鏡観察結果と比較検討し、液晶表面配向の観察における3次元サーフェスプロファイラーの有用性を明らかにしている。
　第6章「Investigation of Alignment of Nematic Liquid Crystals at Micropatterned Polyimide Surface: Exposure Type I」では、サブミクロンサイズで垂直配向領域と水平配向領域を交互に設けたパターン表面での液晶配向を有限要素法によって解析し、この構造が液晶の双安定性配向を示すことを明らかにしている。また、325nmHe-Cdレーザ光を0.5μm line and space のフォトマスクを通して垂直配向用Polyimideに照射し（偏光方向がlineに垂直）、実際に垂直配向領域と水平配向領域を交互にストライプ状に設けたパターン表面を作製し、その基板と、対向基板として均一配向（水平配向、垂直配向）基板を用いた液晶セルで双安定配向を確認している。
　第7章「Microscopic Investigation of Memory Effect found in Micropatterned Nematic Liquid Crystal Cells」では、第6章で述べたパターン基板の表面配向が、対向基板である無処理ITO基板にどのように転写されるかを調べている。
　第8章「Investigation of Alignment of Nematic Liquid Crystals at Micropatterned Polyimide Surface: Exposure Type II」では、第6章と同様な研究を325nmHe-Cdレーザ光をその偏光方向がlineに平行になるように照射したパターン表面について行っており、この場合も双安定配向が得られることを示している。
　第9章「Conclusions」では本研究で得られた結論をまとめている。
　以上のように、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。