No description available.

No description available.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23696号 / 理博第4786号 / 新制||理||1685(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 松田 祐司, 教授 柳瀬 陽一, 教授 石田 憲二 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Chiral nematic liquid crystals or cholesteric liquid crystals (CLC) can be obtained by adding a chiral dopant into a nematic liquid crystal. Liquid crystal molecules spontaneously rotate along a long axis to form helical structures in CLC system. Both pitch size and orientation of the helical structure is determined by the boundary conditions and can be further tuned by external stimuli. Particularly, the uniform lying helical structure of CLC has attracted intensive attention due to its beam steering and diffraction abilities. Up to now, studies have worked on controlling the in-plane orientation of lying helix through surface rubbing and external stimuli. However, it remains challenging to achieve steady and uniform lying helical structure due to its higher energy, comparing with other helical configurations. Here, by varying the surface anchoring, uniform lying helical structure with long-range order is achieved as thermodynamically stable state without external support. Poly (6-(4-methoxy-azobenzene-4'-oxy) hexyl methacrylate) (PMMAZO), a liquid crystalline polymer, is deposited onto the silicon substrate to fine-tune the surface anchoring. By changing the grafting density of PMMAZO, both pitch size and orientation of lying helical structure are precisely controlled. As the grafting density increases, the enhanced titled deformation of helical structure suppresses the pitch size of CLC at the same cell thickness; as the cell thickness increases, the morphology transition from long-range order stripe to small fingerprint domain is facilitated.

Eksperimentai buvo atliekami su bandinėliais gautais iš Madrido, Maskvos ir St.Peterburgo, tai yra su fotoniniais kristalais. Darbe buvo nagrinėta fotoninio kristalo opalo struktūrą ir optines savybes draustinės stop juostos srityje bei defektų valdymo būdai, keičiant elektrinį lauką. Nagrinėjamas elektrinio lauko poveikis defektams, stop juostai. Nustatyta, kad elektriniame lauke susikuria defektai, kuriuos galima valdyti nuo 0V iki 7V įtampos intervale. Išmatuoti defektinės modos perjungimo laikai kurie sieka 200 s, tai 10 kart greičiau nei stop juostos. / We did structural and spectroscopic studies of bulk and thin film synthetic opal. Demonstrate that the photonic crystal, opal have defects, but these defects may be "good" when use it to control light in stop band.

This thesis presents a series of studies of quenched random disorder (QRD) on liquid crystals. We have used high-resolution AC-Calorimetry, high-resolution X-Ray Diffraction (XRD), X-Ray Intensity Fluctuation Spectroscopy (XIFS), Turbidity, Integrated Low-Angle Light Scattering (ILALS), as well as Polarizing Microscopy to characterize the effects of a nano-colloidal dispersions of aerosils in the phase transitions of several liquid crystals. The aerosil ($SIL$) is made of 70~AA~ diameter SiO$_{2}$ particles coated with hydroxyl (-OH) groups. The coating allows the $SIL$ particles to hydrogen-bond together, to form a very low density gel in an organic solvent. This provides the quenched random disorder. The liquid crystals of interest are: octyloxycyanobiphenyl ($8OCB$), 4-extit{n}-pentylphenylthiol-4'-extit{n}-octyloxybenzoate (ar{8}$S5), 4'-transbutyl-4-cyano-4-heptyl-bicyclohexane ($CCN47$), and octylcyanobiphenyl ($8CB$). Studies have been carried out as a function of aerosil concentration and temperature spanning the following phase transitions, Isotropic to Nematic (emph{I-N}), nematic to smectic-emph{A} (emph{N-SmA}), smectic-emph{A} to smectic-emph{C} (emph{SmA-SmC}), and crystallization.

No description available.

No description available.

Esta pesquisa mostrou a viabilidade técnica da utilização de células de cristais líquidos nemáticos (CLNs) como elementos sensores eletro-ópticos de tensões elétricas eficazes (RMS). Duas foram as filosofias abordadas na concepção desses sensores: a modulação em amplitude da intensidade da luz polariza atuando em células transmissivas e a tensão de Freedericksz atuando em células reflexivas. Os sensores baseados na primeira filosofia foram denominados, nesta pesquisa, de sensores de escala de cinza (EC) e os segundos de sensores de gráfico de barras (GB). O sensor EC foi desenvolvido para aplicações em altas tensões. Este sensor é constituído por um divisor de tensão capacitivo, onde o braço de baixa tensão é composto por uma célula de cristal nemático torcida (CLNT). O sensor EC alia as vantagens dos tradicionais sistemas eletro-ópticos, tais como a imunidade às interferências eletromagnéticas (IEM); o alto isolamento elétrico proporcionado pela fibra óptica; com as vantagens de ser um sistema com um simples aparato óptico, então indutivo. O sensor GB mostrou-se mais versátil que o sensor EC. Neste sensor o braço de alta tensão do divisor de tensão capacitivo foi confeccionado na própria célula. Além disso, o sensor GB é menos sensível a influências térmicas, sendo neste caso mais indicado para aplicações de campo. Além das vantagens citadas acima, os sensores desenvolvidos apresentam as características de possuírem baixo custo, facilidade de instalação, versatilidade e empregarem tecnologia nacional. Também neste trabalho, foram estudados e determinados modelo físicos e elétricos que melhor representam o comportamento das células de CLNs. Os modelos físicos permitiram expandir o conhecimento sobre o comportamento de dispersão dielétrica presente nestes materiais devido ao movimento de impurezas iônicas; ao movimento molecular, e ao acúmulo de cargas espaciais nas interfaces entre as camadas de alinhamento e o cristal líquido, e também, auxiliaram na compreensão dos parâmetros físicos que influenciam no comportamento anisotrópico da permissividade dielétrica e da condutividade elétrica dos CLNs. Os modelos elétricos, além de auxiliarem na compreensão dos mecanismos físicos auxiliando com isso a proposição de modelos fenomenológicos, também mostraram-se uma poderosa ferramenta a ser aplicada na otimização de processos de fabricação e no desenvolvimento de dispositivos utilizados na confecção de mostradores de informação (LCDs). Estes modelos elétricos foram testados e utilizados em programas computacionais dedicados à simulação de circuitos elétricos, e puderam auxiliar sobremaneira no desenvolvimento do sensor GB. / In this research the technical viability of the usage of nematic liquid crystal (NLC) cells as sensor elements of effective electric voltage (RMS) is presented. Two approaches were adopted for the conception of these sensors: the modulation in width of the intensity of the polarized light acting in transmissive cells and the voltage of Freedericksz acting in reflexive cells. The sensors based on the first approach were termed grayscale sensors and the second were bargraph sensors. A grayscale sensor was developed for applications in high voltage. This sensor is constituted by a capacitor voltage divider, where the low voltage arm is composed of a cell of twisted nematic liquid crystal (TNLC). The grayscale sensor combines the advantages of traditional electro-optical systems, such as immunity to the electro-magnetic-interference (EMI) and the high electric insulation provided by the optical fiber; associated to characteristics of being a simple optical apparatus and a non-inductive system. The bargraph sensor has shown to be more versatile than the grayscale sensor. In this bargraph sensor the high voltage arm of the capacitor voltage divider was built in the CLNT cell itself, facilitating its use in both high and low voltages. Besides, the bargraph sensor is less sensitive to thermal influences, being in this case more suitable to field applications. In addition to the advantages mentioned above, both sensors developed showed characteristics of low cost, installation easiness, versatility and indigenous technology. Due to the need of establishing parameters for the development of the electric voltage sensor, also in this research, physical and electric models that best represent the behavior of NLC cells were obtained. The physical models allowed expanding the knowledge about the behavior of dielectric dispersion present in these materials due to the movement of ionic impurities, molecular movement, and the accumulation of space charge in the interfaces between the alignment layers and the liquid crystal. These models have also contributed to the understanding of the physical parameters that influence the anisotropic behavior of both dielectric permittivity and electric conductivity of NLCs. Besides, the electric models helped in the understanding of the physical mechanisms aiding in the proposition of phenomenological models. They have also proved to be a powerful tool to be applied in the optimization of production processes, as well as in the development of devices used in liquid crystal displays (LCDs). These electric models were tested and used in software for the simulation of electric circuits and could aid greatly in the development of bargraph sensors.

<p>In recent years portable electronic devices, such as mobile phones and personal digital assistants, have increased the demand for high performance displays with low power consumption. An interesting candidate with the potential of fulfilling these demands is the reflective single-polarizer surface controlled bistable twisted nematic liquid crystal display. The main focus of this work involves the optical properties of displays based on these bistable structures. In the investigations, the display is considered as an integrated optical system, containing not only the liquid crystal cell, but also components such as polarizers and retardation films. The specific aim of the thesis was to derive new optical modes of the reflective single-polarizer bistable twisted nematic device using the Jones matrix method to study the interaction between the polarization of light and the optically anisotropic media. The electro-optical properties of the derived modes have been studied and evaluated both theoretically and experimentally. The modes possess excellent brightness and high contrast ratio. By introducing a quarter-wave retardation film into the optical configuration, the contrast ratio can be significantly increased by preventing spectral leakage of light in the dark state. To experimentally realize the derived optical modes, special layers for the alignment of the liquid crystal molecules on the cell substrate surface have been proved needed. Therefore, also the photo-alignment technology of nematic liquid crystals on novel alignment materials has been studied with the aim to control liquid crystal cell parameters such as pretilt angle and anchoring energy, both critical for the bistable switching. The results of this thesis will increase the understanding of the optical properties of the reflective single-polarizer bistable twisted nematic liquid crystal display and will be valuable when considering this type of device for practical applications.</p>