In this thesis, based on the Onsager excluded volume interaction model, two nematic ordering problems of wormlike (semiflexible) polymer are studied: one is to investigate the isotropic-nematic interface of polymers for three typical cases&mdash;the flexible one, the rigid-rod one and the intermediate one; the other is to investigate a very long polymer confined between two infinite flat hard walls. <br /><br /> Many previous studies of the isotropic-nematic phase coexistence are mainly focused on either rigid rod-like polymers with small flexibility, or flexible polymers with large flexibility. The phase coexistence of polymers with intermediate flexibility is desired to be investigated. For these three typical cases (flexible, rigid-rod and intermediate), the profiles for density, order parameter and tension contribution were shown for different tilt angles. The interface tension was studied. The simulation results are consistent with those reported by other people. <br /><br /> We investigated the confinement of a long polymer between two flat hard walls, which are separated by a distance comparable to the effective Kuhn length of polymer chain by the wormlike chain model with or without the Onsager excluded volume interaction. Without the interaction, the results are compared with those of the Gaussian chain model. Including the interaction, the phase diagram is analyzed.

In this thesis, based on the Onsager excluded volume interaction model, two nematic ordering problems of wormlike (semiflexible) polymer are studied: one is to investigate the isotropic-nematic interface of polymers for three typical cases&mdash;the flexible one, the rigid-rod one and the intermediate one; the other is to investigate a very long polymer confined between two infinite flat hard walls. <br /><br /> Many previous studies of the isotropic-nematic phase coexistence are mainly focused on either rigid rod-like polymers with small flexibility, or flexible polymers with large flexibility. The phase coexistence of polymers with intermediate flexibility is desired to be investigated. For these three typical cases (flexible, rigid-rod and intermediate), the profiles for density, order parameter and tension contribution were shown for different tilt angles. The interface tension was studied. The simulation results are consistent with those reported by other people. <br /><br /> We investigated the confinement of a long polymer between two flat hard walls, which are separated by a distance comparable to the effective Kuhn length of polymer chain by the wormlike chain model with or without the Onsager excluded volume interaction. Without the interaction, the results are compared with those of the Gaussian chain model. Including the interaction, the phase diagram is analyzed.

In this study, a high power Q-switch pulse laser has been used as the writing beams. The laser-induced holographic gratings in the DR1-doped liquid crystal samples and the DR1-PMMA polymer thin films were investigated by changing the temperature of samples and the angles of two writing beams. The He-Ne cw laser has been used as a real-time probe beam to detect the first order diffraction signals. Without external field, the gratings are the results of concentrations and diffusions of azo dye isomers. The diffusion model has been utilized to analyze the first order diffraction signals in order to understand the mechanics of gratings and the effect of temperature and angle.

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The aim of the thesis was to identify and hence investigate the physical properties of liquid crystals that influence their potential as components of biosensor devices. Silicon surfaces presenting photolithographically fabricated arrays of 50nm thick gold spots were used as the model for a biosensor that detects the surface binding of a biological analyte. The spots ranged in diameter from 2μm to 16μm and their spatial separation varied between 5μm to 40μm. A Self Assembled Monolayer (SAM) of the thiol 3-mercaoptopropionic acid was used to control the surface chemistry of the gold. The responses of the nematic liquid crystals 5CB, E7, ZLI 1695, ZLI 1132 and MDA 01-2012 to were measured by optical microscopy. The spots were seen to induce a tilted planar alignment in the liquid crystals in their nematic phase for spot diameters down to 4μm and for all separations. Anchoring transitions between different tilt angles were observed between spots for some arrays. This was linked to a change in anchoring energy at the gold, possibly stemming from the angle of gold deposition. When heated through the nematic to isotropic phase transition cross defects were observed to nucleate on the gold spots for all spot sizes above 4μm. On cooling through the transition grid patterns of defects were observed to nucleate pinned between the spots for arrays of spots with length scales between 10μm and 20μm. The birefringence and elastic constants K11 and K33 of the liquid crystals were measured for temperatures up to their nematic to isotropic transition points. The birefringences of the liquid crystals at the transition were found to range between 0.003 and 0.007. The device thickness was varied between 7μm and 40μm. Values for the elastic constants were found to range between 1pN and 4pN. The intensity of monochromatic light (670nm) reflected from the arrays as the liquid crystals were cooled through the phase transition was found to increase for smaller values of the elastic constants and found to be highest where the grid of defects on the array was observed most clearly. The effect on the intensity of the birefringence and cell thickness was shown to be small compared to the effect of elasticity. Two possible biosensor designs are proposed. The first would identify the presence of a biological analyte at a surface by the change in alignment of a liquid crystal. This type of sensor would be optimised by carefully controlling the anchoring energy of the liquid crystal at the surface to minimise the quantity of surface binding required to induce an anchoring transition. The second would detect the presence at a patterned surface of an analyte by the defects that form over the pattern as the liquid crystal changes between the nematic to isotropic phases. This type of sensor would be optimised by choosing a liquid crystal with small elastic constants at the phase transition and by designing a patterned surface with length scales between 10microns and 20microns.

Nonlinear, nonlocal optical media has emerged as an ideal setting for experimentally observing and studying spatial optical solitary waves which otherwise cannot occur in Kerr media. Of particular interest is the eventual application to all-optical circuits. However, there is considerable work left to do on the theoretical end before this is a possibility. In this thesis we consider three problems. The first is how to solve the governing equations for optical beam propagation in the particular medium of the nematic liquid crystal (NLC), which is used as a prototypical example, exactly and approximately. In this respect we provide the first known, explicit solutions to the model as well as a comprehensive assessment on how to use variational, or modulation theory, in this context. This leads to the discovery of a novel form of bistability in the system, which shows there are two stable solitary wave solutions for a fixed power or L2 norm. We then consider how to approximate solutions for optical solitary waves propagating in a more general class of nonlocal nonlinear media using asymptotic methods. This is a long open problem and is resolved in the form of a simple to implement method with excellent accuracy and general applicability to previously intractable models. We conclude with the discovery and characterization of an instability mechanism in a coupled, defocussing nonlinear Schrodinger system. We show there is no stable, coupled, localized solution. This result is compared with the more well-studied bright solitary wave system and physical and mathematical explanations are offered.

This thesis comprises an account of research carried out into the flexoelectro-optic effect, as observed in chiral nematic liquid crystals, and its potential for application in fibre optic communications components. The flexoelectro-optic effect provides a mechanism of fast, analogue rotation of the optic axis in chiral nematic materials via the application of an electric field to the sample. In particular, bimesogenic liquid crystal materials exhibit very large flexoelectro-optic tilt angles, and a large tilt angle per unit field in comparison to other mesogenic materials. In this work a new geometry for the flexoelectro-optic effect is developed in which the chiral nematic liquid crystal is aligned with its helical axis along the normal to the cell walls and the electric field is applied in the plane of the cell. It is shown that polymer stabilization of this device by the addition of a small percentage of reactive mesogen to mixture increases greatly the ability of the device to withstand high amplitude a.c. electric fields. Applied fields of up to 6.8 V/μm are shown to induce a maximum birefringence of ∆n=0.037, due to both flexoelectric and dielectric coupling, and ∆n=0.012 due to flexoelectric coupling only in a sample based on symmetric difluorinated bimesogens. This induced birefringence is shown to consistently respond to field application and removal on the sub millisecond timescale. Polymer stabilization of the same mixtures in the uniform lying helix texture is shown to affect the electro-optic response of the samples in a manner which is dependent on the concentration of reactive mesogen used, and the temperature at which the reactive mesogen is cured. A concentration of approximately 3% weight/weight, however, has little detrimental impact on the device characteristics, and curing of the sample at the lower end of the chiral nematic temperature range is shown to allow optimization of both tilt angle and response time of the samples. The effect is also employed to demonstrate a new method of fast electrical tuning of the output wavelength from chiral nematic photonic band edge lasers. An 8nm shift was induced in these devices by a 3.5 V/μm applied field.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23452号 / 理博第4746号 / 新制||理||1680(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 石田 憲二, 教授 柳瀬 陽一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22822号 / 理博第4632号 / 新制||理||1666(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 山本 潤, 教授 佐々 真一, 准教授 荒木 武昭 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

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