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Ferris, Andrew J. PhD. "Chiral Induction and Defect Structures in Liquid Crystal Systems." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case159293629900968.
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Kasch, Nicholas. "Liquid crystal-polymer composites and the stabilisation of defect phases." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/liquid-crystalpolymer-composites-and-the-stabilisation-of-defect-phases(ee813754-56cd-493c-a631-d58b06d03c00).html.
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A simple method for increasing the stable temperature range of the liquid crystalline blue phase is demonstrated, by mixing a non-mesogenic polymer of low molecular weight into the blue phase material. In a mixture of cholesteryl benzoate and cholesteryl nonanoate the addition of polystyrene increased the stable blue phase range from 0.5K to 12K. This was measured strictly on heating from the chiral nematic phase through the blue phase in order to minimise non-equilibrium effects, and is one of the largest ranges so measured. The stability range can be closely tuned by changing the polymer concentration and molecular weight. The maximum range found by adding a particular compound seems only to depend on its saturation point in the liquid crystal, and the dependence of the range on concentration is non-linear. These features were explained by a numerical model of a blue phase unit cell incorporating the mean field Flory-Huggins and Maier-Saupe theories where the polymer could fill the high energy defect regions. Two of the oligomers which are shown to stabilise the blue phase are fluorescent, at 450nm and 500nm respectively, and it is proposed that tests on these mixtures could reveal photonic effects caused by the concentration of the fluorophores in the blue phase defect regions. The twist-grain boundary (TGB) phase is present in mixtures of cholesteryl oleyl carbonate and cholesteryl nonanoate over a range of up to 0.3K. The addition of polystyrene has no effect on the stability of the TGB phase. Conventional, in situ UV-initiated polymer stabilisation does not appear to stabilise the TGB phase, but is capable of stabilising over at least 30K the micron-size filaments which appear in the TGB phase when it is heated from the smectic phase in a cell with homeotropic alignment. Some notes are made on the causes and structure of this filament texture, and it is observed that the filaments tend to grow with a characteristic curvature. It is shown theoretically that the correct material could stabilise the TGB phase similarly to the polymers in the blue phase, by extending the previous model to include the Kobayashi-McMillan theory of smectic ordering. A second theoretical model of chirality around the transition to the smectic phase is then presented which takes account of fluctuations, based on an analogy with the state of a smectic-forming material infiltrated into an aerogel. A phase resembling the TGB phase emerges from this model. The model gives two first order transitions in accordance with experiments on the TGB phase, and reflects other experimental pitch and calorimetry measurements too. The electrochemical polymerisation of an acrylate monomer in the nematic and smectic-C* phases is investigated. 30-100V is applied across a cell containing the liquid crystal-monomer mixture, with no additional initiating compound. In both phases, the texture during polymerisation is frozen in by the polymer formed. In a nematic phase in a cell with initially planar alignment, the director in the field off state can be observed to tilt toward the homeotropic over a number of hours. In the ferroelectric case, as well as the textural freezing there is a somewhat reversible agglomeration of polymer strands into micron-scale structures. Scanning electron microscopy reveals a range of structures on both electrode surfaces, including in the nematic case corrugations with a periodicity of 500-750nm. There is no evidence of a polymer network spanning the thickness of the cell - rather the liquid crystal seems to be realigned by a polymer film at the electrode surfaces.
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Afghah, Seyedeh Sajedeh. "MODELING SKYRMIONS, DEFECT TEXTURES, AND ELECTRICAL SWITCHINGIN LIQUID CRYSTALS." Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1532952208004472.
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Zhang, Chiqun. "Theory and Computation of Line Defect Fields in Solids and Liquid Crystals." Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/1058.
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The theory and computation of line defects are discussed in the context of both solids and liquid crystals. This dissertation includes four parts. The Generalized Disclination theory is discussed and applied to numerous interfacial and bulk line defect problems. An augmented Oseen-Frank energy as well as a novel 2D-model is proposed and demonstrated for disclination dynamics in liquid crystal. A model based on kinematics and thermodynamics is devised to predict tactoid dynamics during the process of the isotropic-nematic phase transition in LCLC. In the first part of the thesis, the utility of the notion of generalized disclinations in materials science is discussed within the physical context of modeling interfacial and bulk line defects. The Burgers vector of a disclination dipole in linear elasticity is derived, clearly demonstrating the equivalence of its stress field to that of an edge dislocation. An explicit formula for the displacement jump of a single localized composite defect line in terms of given g.disclination and dislocation strengths is deduced based on the Weingarten theorem for g.disclination theory at finite deformation. The Burgers vector of a g.disclination dipole at finite deformation is also derived. In the second part, a numerical method is developed to solve for the stress and distortion fields of g.disclination systems. Problems of small and finite deformation theory are considered. The fields of various line defects and grain/phase boundary problems are approximated. It is demonstrated that while the far-field topological identity of a dislocation of appropriate strength and a disclinationdipole plus a slip dislocation comprising a disconnection are the same, the latter microstructure is energetically favorable. This underscores the complementary importance of all of topology, geometry, and energetics (plus kinetics) in understanding defect mechanics. It is established that finite element approximations of fields of interfacial and bulk line defects can be achieved in a systematic and routine manner, thus contributing to the study of intricate defect microstructures in the scientific understanding and predictive design of materials. In the third part, nonsingular disclination dynamics in a uniaxial nematic liquid crystal is modeled within a mathematical framework where the kinematics is a direct extension of the classical way of identifying these line defects with singularities of a unit vector field representing the nematic director. We devise a natural augmentation of the Oseen-Frank energy to account for physical situations where infinite director gradients have zero associated energy cost, as would be necessary for modeling half-integer strength disclinations within the framework of the director theory. A novel 2D-model of disclination dynamics in nematics is proposed, which is based on the extended Oseen-Frank energy and takes into account thermodynamics and the kinematics of conservation of defect topological charge. We validate this model through computations of disclination equilibria, annihilation, repulsion, and splitting. In the fourth part, the isotropic-nematic phase transition in chromonic liquid crystals is studied. We simulate such tactoid equilibria and dynamics with a model using degree of order, a variable length director as state descriptors, and an interfacial descriptor. We introduce an augmented Oseen-Frank energy, with non-convexity in both interfacial energy and the dependence of the energy on the degree of order. A strategy is devised based on continuum kinematics and thermodynamics. The model is used to predict tactoid dynamics during the process of phase transition. We reproduce observed behaviors in experiments and perform an experimentally testable parametric study of the effect of bulk elastic and tactoid interfacial energy constants on the interaction of interfacial and bulk fields in the tactoids.
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Murray, Bryce S. Murray. "Anchoring-Induced Topological Defects in Nematic Liquid Crystals: Core Relaxation Mechanisms and Electro-Optics." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1531143058239933.
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Angelo, Joseph S. Angelo. "Direct Mechanical Observation of Surface Anchoring and Disclinations Using Dynamically Reconfigurable Liquid Crystal Cell." Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1532646624675951.
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Schulz, Benjamin, Daniela Täuber, Jörg Schuster, Thomas Baumgärtel, and Borczyskowski Christian von. "Influence of mesoscopic structures on single molecule dynamics in thin smectic liquid crystal films." Universitätsbibliothek Chemnitz, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-122240.
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Mesoscopic structures in liquids have an impact on the diffusion dynamics of the constituting molecules. Smectic 8CB liquid crystals on silicon wafers show the formation of mesoscopic structures on the μm scale at a film thickness of 200 nm. Depending on the kind of substrate (thermally grown or native SiOx), we observed the formation of focal conic domains (FCDs) and a new type of terraced holes, respectively. Dynamics are described via single perylene diimide tracer molecule tracking of translational diffusion and in the case of FCDs by a combination of translation and rotation detected via fluorescence correlation spectroscopy. Tailoring perylene diimide molecules such that the optical transition dipole moment follows the liquid crystal director allows mapping out FCDs and investigating the dynamics within a single FCD.
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Jiang, Miao. "DESIGNS AND APPLICATIONS OF PLASMONIC METAMASKS FOR TOPOLOGICAL DEFECT ENGINEERING AND MANUFACTURING OF PANCHARATNAM FLAT OPTICAL ELEMENTS." Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1533742796947775.
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Schulz, Benjamin, Daniela Täuber, Jörg Schuster, Thomas Baumgärtel, and Borczyskowski Christian von. "Influence of mesoscopic structures on single molecule dynamics in thin smectic liquid crystal films." Soft Matter, 2011,7, S. 7431-7440, 2011. https://monarch.qucosa.de/id/qucosa%3A19943.
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Mesoscopic structures in liquids have an impact on the diffusion dynamics of the constituting molecules. Smectic 8CB liquid crystals on silicon wafers show the formation of mesoscopic structures on the μm scale at a film thickness of 200 nm. Depending on the kind of substrate (thermally grown or native SiOx), we observed the formation of focal conic domains (FCDs) and a new type of terraced holes, respectively. Dynamics are described via single perylene diimide tracer molecule tracking of translational diffusion and in the case of FCDs by a combination of translation and rotation detected via fluorescence correlation spectroscopy. Tailoring perylene diimide molecules such that the optical transition dipole moment follows the liquid crystal director allows mapping out FCDs and investigating the dynamics within a single FCD.
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Wang, Mengfei Wang. "Photo-alignment of orientationally patterned surface for disclination generation and optical applications." Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent153273906099599.
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Kurz, Günter. "Hydrodynamics of defects in nematic liquid crystal films." Thesis, King's College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313591.
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Barboza, Raouf. "Solitons spatiaux et vortex optiques dans les cristaux liquides nématiques." Phd thesis, Université Nice Sophia Antipolis, 2013. http://tel.archives-ouvertes.fr/tel-00949652.
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Les cristaux liquides ont été tout le long un terrain fertile pour la recherche scientifique, des mathématiques à la science des matériaux, à l'optique. Leur utilisation ne se limite pas seulement à l'optique d'afficheurs mais s'étend à l'optique non linéaire, par exemple, à la commutation et au routage de faisceaux optiques. En raison de leur extrême sensibilité aux champs électriques, et ce sur une plage de fréquences allant du continu aux fréquences optiques, ils sont aussi utilises comme milieu non linéaires aptes à générer des faisceaux optiques auto-confinés, appelés solitons spatiaux optiques, à de très faibles puissances. Ces faisceaux ont la propriété de se propager sans diffraction, du fait que cette dernière est compensée par l'auto-focalisation non linéaire du milieu, avec formation de guides d'onde auto-induites. Dans les cristaux liquides nématiques, ces guides d'ondes peuvent à leur tours confiner et guider d'autres signaux optiques et peuvent être reconfigurés, soit optiquement, soit électriquement, du fait que la trajectoire des solitons peut être contrôlée par d'autres champs, ouvrant ainsi la voie à la manipulation tout-optique. Récemment, les cristaux liquides nématiques ont été également utilisés avec succès dans l'optique dite singulière, dans laquelle le paramètre clef est la singularité topologique portée par la phase de l'onde électromagnétique. Dans cette thèse, je rendrai compte de mon travail sur les solitons optiques spatiaux et les singularités optiques dans les cristaux liquides nématiques.
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Pourmatin, Hossein. "Computational Multiscale Methods for Defects: 1. Line Defects in Liquid Crystals; 2. Electron Scattering in Defected Crystals." Research Showcase @ CMU, 2014. http://repository.cmu.edu/dissertations/458.
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In the first part of this thesis, we demonstrate theory and computations for finite-energy line defect solutions in an improvement of Ericksen-Leslie liquid crystal theory. Planar director fields are considered in two and three space dimensions, and we demonstrate straight as well as loop disclination solutions. The possibility of static balance of forces in the presence of a disclination and in the absence of ow and body forces is discussed. The work exploits an implicit conceptual connection between the Weingarten-Volterra characterization of possible jumps in certain potential fields and the Stokes-Helmholtz resolution of vector fields. The theoretical basis of our work is compared and contrasted with the theory of Volterra disclinations in elasticity. Physical reasoning precluding a gauge-invariant structure for the model is also presented. In part II of the thesis, the time-harmonic Schrodinger equation with periodic potential is considered. We derive the asymptotic form of the scattering wave function in the periodic space and investigate the possibility of its application as a DtN non-reflecting boundary condition. Moreover, we study the perfectly matched layer method for this problem and show that it is a reliable method, which converges rapidly to the exact solution, as the thickness of the absorbing layer increases. Moreover, we use the tight-binding method to numerically solve the Schrodinger equation for Graphene sheets, symmetry-adapted Carbon nanotubes and DNA molecules to demonstrate their electronic behavior in the presence of local defects. The results for Y-junction Carbon nanotubes depict very interesting properties and confirms the predictions for their application as new transistors.
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KIM, YOUNGKI. "TOPOLOGICAL DEFECTS IN LYOTROPIC AND THERMOTROPIC NEMATICS." Kent State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=kent1437488066.
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Cronin, Thomas. "Liquid crystal biosensors." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/liquid-crystal-biosensors(428e3ba0-bf7e-4dda-9eae-c44c9713c7bb).html.
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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.
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Tang, Xingzhou. "Defect structure and dynamics in liquid crystals." Kent State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=kent1595437628350299.
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Rafayelyan, Mushegh. "Singular beam shaping from spin-orbit flat optics." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0583/document.
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Dans ce travail nous avons résolu deux problèmes principaux de la mise en forme topologique de faisceau paraxial pour les composants plans : la modalité et le polychromatisme.Nous les résolvons en introduisant de nouveaux concepts d’éléments optiques à interaction spin orbite,à savoir la “q-plate modale” et la “q-plate Bragg-Berry”. D’un côté, la q-plate modale convertit un faisceau gaussien incident en un faisceau de Laguerre-Gauss pour un indice radial et un indice d’azimut donnés, ce qui par conséquent dépasse les capacités des q-plates conventionnelles qui ne modifient que le degré de liberté azimutal, c.à.d. le moment orbital angulaire de la lumière. À des fins expérimentales, deux approches ont été développées : une basée sur des lames de verres nanostructurées artificiellement, l’autre sur des défauts topologiques de cristaux liquides auto-organisés naturellement. D’un autre côté, la q-plate Bragg-Berry consiste en une fine couche inhomogène de cristaux liquides chiraux (cholestériques) devant un miroir, ce qui fournit une mise en forme de faisceau spin-orbite pleinement efficace sur une large bande spectrale du faisceau incident, contrairement au q-plates conventionnelles qui ne sont fabriqués que pour une longueur d’onde donnée. Par ailleurs, nous obtenons une mise en forme de faisceau spin-orbite ultra-large bande en induisant une modulation de la structure supramoléculaire torsadée des cristaux liquides cholestériques selon la direction de propagation de la lumière. Nous montrons également que la présence du miroir derrière permet un puissant contrôle spatio-temporel des propriétés vectorielles de la polarisation du champ lumineux générées par la q-plate Bragg-BerryIt is well-known that paraxial coherent electromagnetic fields can be completelycharacterized in terms of their radial and azimuthal spatial degrees of freedom in the transverse planethat add to the polarization degree of freedom and wavelength. In this work we address two mainissues of paraxial beam shaping that are the modality and the polychromaticity in the context of flatopticsthat we address by introducing novel concepts of spin-orbit optical elements. Namely, the‘modal q-plate’ and the ‘Bragg-Berry q-plate’. On the one hand, modal q-plate converts an incidentfundamental Gaussian beam into a Laguerre-Gaussian beam of given radial and azimuthal indices,hence going beyond the capabilities of conventional q-plates that only control the azimuthal degreeof freedom, i.e. the orbital angular momentum content of light. Towards experimental realization ofmodal q-plates, two approaches are developed: one based on artificially nanostructured glasses andanother based on naturally self-organized liquid crystal topological defects. On the other hand,Bragg-Berry q-plate consist of mirror-backed inhomogeneous thin film of chiral liquid crystal(cholesteric) that provides fully efficient spin-orbit beam shaping over broad spectral range of theincident beam, in contrast to the conventional q-plates that are designed for single wavelength.Furthermore, ultra-broadband spin-orbit beam shaping is achieved by inducing an extra modulationof the supramolecular twisted structure of the cholesteric liquid crystal along the propagationdirection. We also show that the presence of a back-mirror allows a powerful spatio-temporal controlof the polarization vectorial properties of the light fields generated by Bragg-Berry q-plate
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De, Luca Gino. "Computational modelling of nematic liquid crystal defects in devices and fiber processing." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103377.
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This thesis uses multiscale computational modelling to find the fundamental principles that govern defects forming during the operation of new electro-optical devices and the processing of spider silk fibers. The generalized approach developed in this thesis bridges engineering devices and biological processes based on liquid crystalline materials.Three types of defects are encountered: inversion walls, lines and points. Inversion wall defects are found in the electro-optical device when a nematic thin film undergoes a temperature-induced surface anchoring transition. Point defects naturally occur in the tubular extrusion duct of spiders, while line defects present close topological connections with point defects and are widespread in many high-performance industrial fibers. Three models are used in this thesis and their usage is dependent on the characteristics of the defects studied.
In the case of inversion wall defects, computational modelling is used to verify, complement and analyze experimental measurements made with fluorescence confocal polarizing microscopy by our collaborator at the Georgia Institute of Technology. The various simulation results agree and explain very well experimental observations and provide a thorough understanding of the wall defects behavior. A computational technique is developed to enable the precise determination of the interaction between the liquid crystal and the device substrate. Understanding the behavior of wall defects and estimating interfacial properties are indispensable to the development and optimization of the electro-optical device as they affect properties like temperature of operation, switching voltages and response time.
Computational modelling is also used to investigate the behavior of nematic point defects confined in cylindrical cavities as observed along spiders' spinning apparatus, and to examined textural connections with other well know structures seen in industrial fibers. The various scenarios investigated include: interactions between point defects, topological transformations between point, line and ring defects as well as interactions between ring defects. The simulation results agree and complement previous investigations but also offer a new fundamental understanding on the nature and stability of defects in cylindrical cavities. Understanding the behavior of nematic point and line defects in cylindrical geometries is important as they play a fundamental role in the processing of natural and industrial high-performance fibers.
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Mehta, Ketan. "NLCViz tensor visualization and defect detection in nematic liquid crystals /." Master's thesis, Mississippi State : Mississippi State University, 2006. http://sun.library.msstate.edu/ETD-db/ETD-browse/browse.
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Lewis, Alexander. "Defects in liquid crystals : mathematical and experimental studies." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:56930aaf-43a5-46bb-9987-109b22950a97.
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Nematic liquid crystals are mesogenic materials that are popular working materials for optical displays. There has been an increased interest in bistable liquid crystal devices which support two optically distinct stable equilibria. These devices typically exploit a complex geometry or anchoring conditions, which often induces defects in the equilibria. There remains a great deal to be understood about the structure of the defects and how they stabilize multiple equilibria in modern devices. This thesis focuses on four problems: the first three explore the effect of confinement and defects on nematic equilibria in simple geometries, with the aim of exploring multistability in these geometries; the fourth problem concerns the fine structure of point defects, essential for future modelling of nematic equilibria in more complex geometries. Firstly, we study nematic liquid crystals confined to two-dimensional rectangular wells using the Oseen-Frank theory. Secondly, we study equilibria within a semi-infinite rectangular domain with weak tangential anchoring on the surfaces. Thirdly, we study nematic equilibria within two-dimensional annuli. We derive explicit expressions for the director fields and free energies of equilibria within these geometries and discuss the stability of the predicted states. These three problems are motivated by the experimental work on colloidal nematic liquid crystals, which we interpret in the context of our results. Finally, we study the fine structure and stability of the radial hedgehog defect in the Landau-de Gennes theory with a sixth order bulk potential, relevant to the observability of global biaxial phases in a model with higher order potential terms.
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Kelly, Gavin. "An analytical and numerical investigation of liquid crystal defects." Thesis, University of Strathclyde, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431822.
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Hazelwood, Lee David. "Theories of defect structures found in smectic-A liquid crystals." Thesis, University of Southampton, 1998. https://eprints.soton.ac.uk/50642/.
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This thesis consists of four studies describing the physical and mathematical modelling of some defect structures found within smectic-A liquid crystalline phases. The first study extends the simple static chevron theories to include variations of both nematic and smectic elastic constants. In the second study the dynamics of chevron formation are investigated. The dynamics are governed by smectic-A hydrodynamics and can be separated into two processes known as mass flow and permeation. Chevron evolution as a result of each process is presented. The symmetry of the chevron structure leads to the existence of two stable polarities. The boundaries between domains of opposing polarities are known more commonly as zig-zag defects. Investigations into the boundary structure is the subject of the third study. The chevron structure is an example of a small angle grain boundary located in the centre of the cell. The structure of large angle tilt grain boundaries are expected to be composed of a different interface structure. This possibility is considered in the fourth study.
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Sasa, Shin-ichi. "Defect Chaos in Electro-Hydrodynamic Convection of Nematic Liquid Crystals." 京都大学 (Kyoto University), 1991. http://hdl.handle.net/2433/168803.
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本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものであるKyoto University (京都大学)
0048
新制・課程博士
理学博士
甲第4702号
理博第1300号
新制||理||722(附属図書館)
UT51-91-E73
京都大学大学院理学研究科物理学第一専攻
(主査)教授 蔵本 由紀, 教授 恒藤 敏彦, 教授 福留 秀雄
学位規則第5条第1項該当
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Jones, Christopher D. "Domains, defects, and de Vries: Electrooptics of smectic liquid crystals." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3284490.
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Nemitz, Ian R. "Liquid Crystals: Surfaces, Nanostructures, and Chirality." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1480686661255562.
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Gunther, Janelle. "Defects in liquid crystal polymers : their origins and behavior in magnetic and flow fields." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/43466.
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Darmon, Alexandre. "Cristaux liquides sur interfaces courbes : élasticité, structure et topologie." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066673.
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Nous présentons des résultats expérimentaux et théoriques sur les cristaux liquides en géométrie courbe. Nous étudions des coques de cristal liquide cholestérique dont la géométrie sphérique impose la présence de défauts topologiques. Ceci en fait un terrain de jeu idéal pour étudier la nature de ces singularités et leurs interactions. Nous observons un total de cinq configurations de défauts différentes, un atout remarquable dans le contexte d’auto-assemblage dans lequel ce projet s’inscrit. Les efforts combinés d’expériences et de simulations numériques nous permettent de décrire avec précision la structure des défauts. La complexité qui caractérise ces nouvelles structures est inhérente à la nature cholestérique de ces mésophases frustrées. Nous montrons qu’il est possible d’induire des transitions entre les différentes configurations, et examinons la dynamique qui y est associée. Nous établissons un modèle théorique qui rend compte de la position des défauts dans les différentes configurations. Nous discutons de l’équilibre subtil entre les interactions élastiques répulsives et le gradient d’épaisseur attractif qui résulte de la nature non-concentrique des coques. En outre, la confrontation du modèle aux expériences nous permet d’estimer les énergies associées aux nouvelles structures de défauts observées. Enfin, nous abordons les géométries toroïdales, et montrons que des transformations de formes peuvent nous permettre d’étudier la genèse et l’annihilation de défauts topologiquesWe present experimental and theoretical results on liquid crystals confined to curved geometries. We study cholesteric liquid crystal shells, the geometry of which imposes the presence of topological defects. This system constitutes an ideal playground to study the nature of these singularities and their interactions. We report a total of five different defect configurations, a remarkable feature in the context of self-assembly in which this work is set. Combining experiments and numerical simulations, we are able to accurately describe the inner structure of all observed defects. The complexity of these new structures is related to the cholesteric nature of the liquid crystal. We show that it is possible to induce transitions between the different configurations, and investigate the associated dynamics. We establish a theoretical model that successfully predicts the equilibrium defect positions in all configurations, and discuss the subtle balance between repulsive elastic interactions and attractive thickness gradients, arising from the eccentricity of the shells. Confronting the model to the experimental data, we are able to estimate the energies of nontrivial defect structures. Finally, we investigate toroidal geometries, and show how shape transformations can be interesting to study the genesis and annihilation of topological defects
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Kim, Min Su. "Liquid Crystalline Amorphous Blue Phase: Tangled Topological Defects, Polymer-stabilization, and Device Application." Kent State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=kent1448894363.
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Sengupta, Anupam. "Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://hdl.handle.net/11858/00-1735-0000-000E-00FA-B.
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Culbreath, Christopher Michael. "Artificial Microscopic Structures in Nematic Liquid Crystals Created by Patterned Photoalignment And Controlled Confinement: Instrumentation, Fabrication and Characterization." Kent State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=kent1424375624.
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Missaoui, Amine [Verfasser], and Ralf [Gutachter] Stannarius. "Dynamics of topological defects in freely floating smectic liquid crystal films and bubbles / Amine Missaoui ; Gutachter: Ralf Stannarius." Magdeburg : Universitätsbibliothek Otto-von-Guericke-Universität, 2021. http://d-nb.info/1239811543/34.
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Senyuk, Bohdan. "Dielectric Response of Liquid Crystals Formed by Bent-Core and Chiral Molecules." Kent State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=kent1290017391.
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Pardaev, Shokir A. "LIGHT SCATTERING STUDIES OF DEFECTS IN NEMATIC/TWIST-BEND LIQUID CRYSTALS AND LAYER FLUCTUATIONS IN FREE-STANDING SMECTIC MEMBRANES." Kent State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=kent1497022792130101.
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Vallvé, Antón Maria dels Àngels. "Sistemes nanoestructurats mitjançant monocapes de Langmuir." Doctoral thesis, Universitat de Barcelona, 2010. http://hdl.handle.net/10803/48668.
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Els treballs presentats en aquesta tesi fan referència a sistemes amb estructures d’escales nanomètriques. L’estructura d'aquests sistemes s’obté mitjançant la formació de monocapes de Langmuir, dipositant dissolucions de molècules amfifíliques o suspensions de partícules col•loïdals sobre la superfície de l'aigua.
Per una banda, s’han preparat monocapes de Langmuir de la molècula fotosensible 8Az3COOH. Mitjançant la tècnica de Langmuir-Blodgett, aquestes monocapes han estat transferides sobre substrats sòlids que, posteriorment, s’han utilitzat per a formar cel•les de cristall líquid. Aquestes permeten visualitzar les estructures transferides, similars a les observades en la monocapa de Langmuir, però no presenten fotosensibilitat. Les monocapes de Langmuir de 8Az3COOH també s’han utilitzat per a estudiar la dinàmica de les estructures i els defectes observats mitjançant microscòpia d’angle Brewster en la monocapa de Langmuir.
Per altra banda, també s’han preparat monocapes de Langmuir-Blodgett de partícules col•loïdals de diòxid de silici per obtenir cristalls col•loïdals bidimensionals amb propietats fotòniques.The works of this thesis are related to systems with structures in the nanoscale. The structure of these systems is obtained by preparing Langmuir monolayers, spreading solutions of amphiphilic molecules or suspensions of colloidal particles on the water surface. On the one hand, Langmuir monolayers of the photosensitive molecule 8Az3COOH have been prepared. These monolayers have been transferred on solid substrates by the Langmuir-Blodgett technique. Later, these substrates have been used to build liquid crystal cells. These cells allow us to visualize the transferred structures, which are similar to those observed in the Langmuir monolayer, but they do not show photosensitivity. The Langmuir monolayers of 8Az3COOH have also been used to study the dynamics of the structures and the defects observed by Brewster angle microscopy in the Langmuir monolayers. On the other hand, Langmuir-Blodgett monolayers of silica particles have been prepared in order to obtain two-dimensional colloidal crystals with photonic properties.
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Souza, Iberê Oliveira Kuntz de 1991. "Geometria dos defeitos topológicos em materiais esméticos sobre superfícies curvas." [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/276959.
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Orientadores: Ricardo Antonio Mosna, Guillermo Gerardo Cabrera OyarzunDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Nesse trabalho estudamos configurações geométricas de um cristal líquido bidimensional sobre substratos curvos. Em particular, estamos interessados na fase esmética-A desses materiais, em que as suas moléculas são organizadas em camadas. Isso é interessante pois grande parte das propriedades de um cristal líquido, como as propriedades ópticas e elásticas, é afetada pela curvatura do seu substrato. Diferentemente dos esméticos no plano euclidiano, em superfícies curvas a presença de curvatura gaussiana dá origem a defeitos topológicos e grain boundaries na estrutura dos esméticos. Mostrarei essa interação entre curvatura e defeitos topológicos em algumas superfícies no limite em que a contribuição à energia devido a compressão das camadas é muito maior do que as contribuições provenientes de outros tipos de deformação. Nesse regime, o estado de menor energia é obtido quando as camadas esméticas são igualmente espaçadas. Isso faz com que o vetor diretor siga as geodésicas da superfície, o que leva a uma interessante analogia entre esméticos e óptica geométrica. Além disso, é bem conhecido na comunidade de óptica que lentes planas de índice de refração não-uniformes podem ser tratadas como superfícies curvas, cujas geodésicas se propagam da mesma forma que a luz se propaga na lente. Com isso, pode-se fabricar, em princípio, superfícies com propriedades ópticas específicas e, dessa forma, construir texturas esméticas com diferentes defeitos e singularidades a partir da extensa literatura conhecida de lentes
Abstract: We study geometrical configurations of liquid crystals defined on curved bidimensional substrates. We are particularly interested in the smectics-A phase, whose molecules are organized in layers. This is an interesting problem since many of the liquid crystal characteristics, such as its optical and elastic properties, are affected by the curvature of its substrate. Differently from the planar case, in curved surfaces the presence of Gaussian curvature induces topological defects and grain boundaries in the smectic structure. We will illustrate this interplay between curvature and topological defects for different surfaces in the limit where the energy contribution due to the compression of the layers is much larger than the contributions from other types of deformations. At this regime, the ground state is obtained when the smectic layers are uniformly spaced. In this case the normals to the layers follows geodesics of the surface. This leads to an interesting analogy between smectics and geometric optics. Moreover, it is well known in the optics community that flat lenses with nonuniform refractive index can be treated as curved surfaces, where their geodesics propagate in the same way that light propagates in the lens. Therefore, one can manufacture, in principle, surfaces with specific optical properties and construct smectic textures with different topological defects and singularities by using the extensive literature of known lenses
Mestrado
Física
Mestre em Física
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Lamy, Xavier. "Autour des singularités d’applications vectorielles en physique de la matière condensée." Thesis, Lyon 1, 2015. http://www.theses.fr/2015LYO10085/document.
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Cette thèse est consacrée principalement à l'analyse mathématique de modèles issus de la physique des cristaux liquides et de la supraconductivité. Ces modèles ont en commun de faire intervenir des systèmes elliptiques dont les solutions présentent des singularités : défauts optiques dans les cristaux liquides, défauts de vorticité en supraconductivité. Les cristaux liquides se composent de molécules allongées qui, tout en étant distribuées « au hasard » comme dans un liquide, tendent à s'aligner dans une direction commune : cet « ordre d'orientation » leur confère des propriétés optiques similaires à celles d'un cristal, à l'origine de leurs nombreuses applications industrielles. On démontre différents résultats liés à la symétrie locale de cet alignement autour des singularités. On présente aussi dans cette thèse différents résultats liés au modèle de Ginzburg-Landau pour les supraconducteurs de type II, et aux « défauts de vorticité » : points isolés autour desquels la supraconductivité est détruite. Une dernière partie de cette thèse traite de la caractérisation de la régularité d'une fonction f à travers la vitesse de convergence de f ∗ ρε pour un certain noyau ρ. Dans un travail commun avec Petru Mironescu, on s'intéresse à la question de la régularité des noyaux ρ qui permettent une telle caractérisationThe present thesis is devoted mainly to the mathematical analysis of models arising in the physics of liquid crystals and superconductivity. A common feature of these models is that one has to deal with elliptic systems whose solutions have singularities: optical defects in liquid crystals, vorticity defects in superconductivity. The rod-like molecules in a liquid crystals, while being (as in a liquid) “randomly” distributed, tend to align in a common direction: this “orientational order” enhances crystal-like optical properties, which are responsible for their many industrial applications. We demonstrate different results related to the local symmetry of this alignement near singularities. We also present some results related to the Ginzburg-Landau model for type II superconductivity, and to “vortices”: isolated points at which superconductivity is destroyed. The last part of this thesis addresses regularity characterization for a function f through the convergence rate of f ∗ ρε, for some kernel ρ. In a joint work with Petru Mironescu we study the minimal regularity of ρ that allows such characterization
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Selmi, Mayada. "Textures à la surface libre de cristaux liquides smectiques : étude en géométrie films librement suspendus et sur substrats structurés." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0098/document.
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Ces travaux concernent l’étude expérimentale des textures se développant dans les ménisques de films smectiques de cristaux liquides thermotropes. Ces fluides complexes nous servent de système modèle pour l’étude des couplages élasto-capillaires qui se manifestent dans certaines conditions par des déformations périodiques de l’interface cristal liquide-air. Dans un premier temps, à partir de l’étude détaillée de la topographie de l’interface par une méthode interférométrique, nous caractérisons les différents types de structures, puis, identifions les principaux paramètres impliqués dans le processus d'apparition des défauts dans le ménisque de films libres suspendus. Ces résultats nous servent de base pour discuter des mécanismes physiques qui génèrent les différents types de défauts observés. Nous regardons en particulier, comment la diminution d’épaisseur de couche associée à une transition de phase va induire une instabilité mécanique responsable de l’apparition des ondulations de l’interface. Dans un deuxième temps, afin d’aller plus loin dans la compréhension des mécanismes, nous avons utilisé des films minces de cristaux liquides déposés sur des substrats solides microstructurés par des plots fabriqués par des techniques photolitographiques. Une telle géométrie permet de générer un ménisque autour de chaque plot et surtout de faire varier un plus grand nombre de paramètres comme par exemple l’ancrage sur le substrat via un traitement chimique de surface. L’ensemble de nos résultats apportent un éclairage nouveau sur la caractérisation et la compréhension des déformations spécifiques aux ménisques de fluides complexesThe present work is an experimental study of the textures that appear in the meniscus of free standing smectic films with thermotropic liquid crystals. These complex fluids serve as model systems to investigate elasto-capillary phenomena which, under certain conditions, manifest themselves through periodic deformations of the liquid crystalair interface. In the first part of the thesis, we focus our attention on meniscus structures whose interfacial topographies are thoroughly characterized thanks to an in-house optical interferometry technique. Our study allows us to identify the main parameters involved in the development of meniscus structures and to discuss the physical mechanisms that are likely to be responsible for their formation. In particular, we show how a phase transition-induced layer shrinkage triggers a mechanical instability leading to interfacial undulations of the smectic free surface. In the second part of the manuscript, we address the case of thin liquid crystal films deposited on solid patterned solid substrates. The latter consist of regular arrays of microposts fabricated through photolithographic techniques. Such a geometry allows a meniscus to be formed around each micropost and makes it possible to examine the influence of other parameters such as the anchoring conditions on the solid substrate. The results gathered so far are able to shed some light on the characterization and the understanding of the specific deformations and textures that appear in the menisci of complex fluids
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Hénon, Sylvie. "Microscopie à l'angle de Brewster : transitions de phases et défauts d'orientation dans des films monomoléculairess." Phd thesis, Université Pierre et Marie Curie - Paris VI, 1993. http://tel.archives-ouvertes.fr/tel-00001113.
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La microscopie à l'angle de Brewster est une nouvelle et tres puissante technique d'étude des films monomoléculaires à la surface de l'eau. Son principe est basé sur les propriétés de réflectivité des interfaces. Elle est sensible à l'épaisseur, la densité et l'anisotropie optique des films. Cette technique a été appliquée à l'étude de couches adsorbées à la surface de solutions aqueuses d'acides gras (acides palmitiques et myristiques). Ces couches traversent pendant leur formation des transitions de phases. Le nombre, la nature et la morphologie de ces phases dépendent de nombreux paramètres dont le pH. Nous avons entre autres observé des phases optiquement anisotropes, contituées de molécules inclinées par rapport à la normale à la solution.Ces phases sont sans doute des mésophases "verrouillées", c'est à dire que la direction des molécules est fixée par rapport aux directions intermoléculaires. Elles présentent différents types de défauts d'orientation, dont des structures en étoile. L'existence de telles structures est expliquée par application d'un modèle d'élasticité continue développé pour l'étude des films minces de cristaux liquides smectiques. Des structures en zig-zag, en spirales et en bandes de largeur déterminée ont également été observées. Nous avons également étudié les couches d'un polymère (le PDMS) à la surface de l'eau. Nous y avons observé la séparation latérale en domaines de densités de surface différentes, à la fois dans le régime monocouche et le régime multicouches.
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Oliveira, Breno Ferraz de. "Estudos numéricos da formação e dinâmica de defeitos topológicos em cristais líquidos nemáticos." Universidade Federal da Paraíba, 2012. http://tede.biblioteca.ufpb.br:8080/handle/tede/5713.
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In this work we study numerically the generation and dynamics of topological defects in nematic liquid crystals. Our study is based on a Ginzburg-Landau model describing the evolution of the orientational order of a liquid crystal in terms of a symmetric, traceless, second-rank tensor. This phenomenological model allows studies of nematic phases at scales ranging from few nanometers to few micrometers (mesoscopic scale). Within this framework we developed a software named LICRA (Liquid CRystal Algorithm) that combines standard finite difference algorithm for the spatial derivatives with a Runge-Kutta temporal integration to solve the relaxational equations of nematodynamics without thermal fluctuations and hydrodynamic flow. Using this software we investigate the coarsening dynamics of defects of two- and three-dimensional uniaxial nematic liquid crystals. The time dependences of the structure factor and characteristic length scale were computed. The characteristic length scale is expected to grow as a power law in time, L ∝ tα. From dimensional analysis α = 1/2 and we found α = 0, 45±0, 01 in two-dimensions and α = 0, 350±0, 003 in three-dimensions. Furthermore, in all cases Porod s law is satisfied for large values of wave number k. We also investigate, using LICRA, the coarsening dynamics of liquid crystal textures in a two-dimensional nematic under applied electric fields. We consider both positive and negative dielectric anisotropies and two different possibilities for the orientation of the electric field parallel and perpendicular to the two-dimensional lattice. We determine the effect of an applied electric field pulse on the evolution of the characteristic length scale and other properties of the liquid crystal texture network. In particular, we show that different types of defects are produced after the electric field is switched on, depending on the orientation of the electric field and the sign of the dielectric anisotropy. Finally, we present the effect of the rotation of an external electric field on the dynamics of half-integer disclination networks in two and three dimensional nematic liquid crystals with a negative dielectric anisotropy. We show that a rotation of π of the electric field around an axis of the liquid crystal plane continuously transforms all half-integer disclinations of the network into disclinations of opposite sign via twist disclinations. We also determine the evolution of the characteristic length scale, thus quantifying the impact of the external electric field on the coarsening of the defect network.
Neste trabalho estudamos numericamente a formação e dinâmica de defeitos topológicos em cristais líquidos nemáticos. Nosso estudo é baseado no modelo de Ginzburg- Landau, o qual descreve a evolução da ordem orientacional de um cristal líquido em termos de um tensor de segunda ordem simétrico e com traço nulo. Este modelo fenomenológico permite estudar a fase nemática em escalas que vão de poucos nanômetros até poucos micrômetros (escala mesoscópica). Para tal estudo numérico, desenvolvemos um programa de computador que denominamos de LICRA (Liquid CRystal Algotithm). Este programa combina o algoritmo de diferença finita para calcular derivadas espaciais com a integração temporal de Runge-Kutta para resolver a equação de relaxação da nematodinâmica, sem a presença de flutuações térmicas e fluxos hidrodinâmicos. Usando este programa de computador investigamos a dinâmica de coalescência em duas e três dimensões em um cristal líquido nemático uniaxial. Tanto o fator de estrutura quando a escala de comprimento característico foram calculadas no tempo. Espera-se que esta escala cresça como uma lei de potências do tempo, L ∝ tα, onde, a partir de uma análise dimensional, α = 1/2. Encontramos os valores de α = 0, 45 ± 0, 01 em duas dimensões e α = 0, 350 ± 0, 003 em três dimensões. Além disso, em todos os casos verificamos que a lei de Porod é satisfeita para número de ondas k de grandes valores. Utilizando LICRA, investigamos também a dinâmica de coalescência de cristais líquidos nemáticos em duas dimensões submetidos a um campo elétrico externo. Consideramos a anisotropia dielétrica positiva e negativa e duas diferentes possibilidades de orientação do campo elétrico: paralelo e perpendicular ao plano da rede bidimensional. Determinamos os efeitos de um pulso de campo elétrico na evolução da escala do comprimento característico e as alterações nas texturas dos cristais líquidos. Em particular, mostramos que os diferentes tipos de defeitos que são produzidos após o campo elétrico ser aplicado dependem da orientação do campo elétrico e do sinal da anisotropia dielétrica. Finalmente, apresentamos os efeitos da rotação de um campo elétrico externo na dinâmica de uma rede de defeitos semi-inteiros em cristais líquidos nemáticos em duas e três dimensões com anisotropia dielétrica negativa. Mostramos que, girando o campo elétrico por um ângulo π ao redor de um eixo pertencente a plano da rede, ocorre uma transformação contínua de todas as desclinações semi-inteiras da rede em desclinações com sinal oposto. Esta transformação é intermediada por desclinações do tipo torção. Além disso, determinamos a evolução da escala de comprimento característico quantificando o impacto do campo elétrico externo na dinâmica de coalescimento da rede.
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Pereira, Erms Rodrigues. "Física dos cristais líquidos e gravitação : pontos de encontro." Universidade Federal da Paraíba, 2011. http://tede.biblioteca.ufpb.br:8080/handle/tede/9546.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
Aspects of the physics of nematic liquid crystals are studied in this thesis from the viewpoint of riemannian geometry through analogue models of gravitation. The topics chosen for study were: geometric and wave optics, elastic waves, hydrodynamics and heat conduction. The main analogue model used is based on the interpretation of Fermat’s principle as a process to obtain null geodesics, where the liquid crystalline material is seen as a riemannian manifold. This approach predicts that the metric effectively felt by the light ray depends on the configuration of molecules in the liquid crystal and on the parallel and perpendicular refractive indexes to the axis of symmetry of the liquid-cristal molecule. It is known that, for the particular case of the existence of topological defects within the material, effective metric similar to cosmological defects (like global monopoles and cosmic strings) are obtained. This thesis develops itself on the situation where there are topological defects of hedgehog type and (k = 1, c = 0) disclination type in the nematic phase of the liquid crystalline material. The first problem studied, as a review, deals with the wave optics, with respect to the light diffracted by the cited defects. Since plane waves of small wavelength have identical trajectories to light rays, the use of analog model is therefore justified. Thus, we show that light scattered by these defects generates a characteristic diffraction pattern, being the location given by an algebraic expression dependent on the parallel and perpendicular refractive indexes to the axis of symmetry of the molecule. We also show how theses patterns depend on the temperature of the material. The second studied problem deals with the geometrical optics and hydrodynamics of the nematic liquid crystals. From a molecular configuration similar to a (k = 1, c = 0) disclination, we let the material flow radially towards the axis of the defect. Then, using the hydrodynamic fact that velocity gradients in the material locally change the refractive index of the molecule, we find the velocity profile that must exist around the defect so that the metric actually experienced by light traveling in the plane perpendicular to the axis the defect is the Schwarzschild one in the equatorial plane, with the Schwarzschild radius interior to the object. We found that the absolute values of the velocity of liquid crystalline fluid can be order of a few meters per second, differing greatly from the values obtained by Gordon metric for an isotropic fluid under identical conditions. The third studied problem deals with the elastic oscillations in the presence of topological defects. Similarly to the first problem, the trajectory of the sound is obtained by an elastic version of Fermat’s principle and, then, compared with a null geodesic. We show how topological defects influence the sound trajectories and the sound diffracted by them. The fourth problem deals with the heat conduction in the vicinity of defects. Considering that the defects come from an addition or removal of portion of the material, letting the medium relaxes elastically, effective metric of the space disturbed by the defect are found, with expressions similar to those obtained by the analogous model based on Fermat’s principle. These metrics generate a modified thermal conductivity tensor, allowing the study of the temperature field in this situation. We show that, depending on the values of parallel and perpendicular thermal conductivity to the axis of symmetry of the molecule and on the defect in question, the temperature gradient can be accentuated or attenuated on the defect, allowing control of the response thermal temperature of the material, according to the presence of defects. Encouraging a greater understanding of the physics of liquid crystals and its use as a background in analogue models of gravity is the main theme of each analyzed problem.
Aspectos da física dos cristais líquidos nemáticos são estudados nesta tese do ponto de vista da geometria riemannina, por meio de modelos análogos de gravitação. Os tópicos escolhidos para estudo foram: óptica geométrica e ondulatória, ondas elásticas, hidrodinâmica e condução de calor. O principal modelo análogo empregado baseia-se na interpretação do princípio de Fermat como um processo de obtenção de geodésicas nulas, onde o material líquido-cristalino é visto como sendo uma variedade riemanniana. Esta abordagem prevê que a métrica efetivamente sentida pelo raio luminoso dependa da configuração das moléculas dentro do cristal líquido e dos índices de refração paralelo e perpendicular ao eixo de simetria da molécula líquido-cristalina. É sabido que, para o caso especial da existência de defeitos topológicos dentro do material, métricas efetivas semelhantes às de defeitos cosmológicos (como monopolos globais e cordas cósmicas) são obtidas. Esta tese desenrola-se sobre a situação onde existem defeitos topológicos do tipo ouriço e do tipo desclinação (k = 1, c = 0) na fase nemática do material líquido-cristalino. O primeiro problema estudado, em caráter de revisão, trata da óptica ondulatória, no que concerne a difração de luz pelos defeitos citados. Uma vez que ondas planas de comprimento de onda pequeno possuem trajetórias idênticas aos raios luminosos, o emprego do modelo análogo é justificado. Assim, mostramos que a luz espalhada por esses defeitos gera padrões de difração bem característicos, sendo a localização dada por expressão algébrica dependente dos índices de refração paralelo e perpendicular ao eixo de simetria da molécula líquido-cristalina. Também mostramos de que forma esses padrões dependem da temperatura do material. O segundo problema estudado trata da óptica geométrica e da hidrodinâmica dos cristais líquidos nemáticos. A partir de uma configuração de moléculas semelhantes à de uma desclinação (k = 1, c = 0), permitimos que o material flua radialmente na direção do eixo do defeito. Em seguida, fazendo uso do fato hidrodinâmico de que gradientes de velocidade no material modificam localmente os índices de refração da molécula, encontramos o perfil de velocidade que deve existir em torno do defeito para que a métrica efetivamente sentida pela luz, que viaja no plano perpendicular ao eixo do defeito, seja a de Schwarzschild no plano equatorial, com raio de Schwarzschild interior ao objeto. Encontramos que os valores absolutos da velocidade de fluido líquido-cristalino podem ser da ordem de alguns metros por segundo, diferindo enormemente dos valores obtidos pela métrica de Gordon para um fluido isotrópico em condições idênticas. O terceiro problema estudado aborda as oscilações elásticas na presença de defeitos. Semelhantemente ao primeiro problema, a trajetória do som é obtida por uma versão elástica do princípio de Fermat e, então, comparada com uma geodésica nula. Mostramos como defeitos topológicos influenciam nas trajetórias sonoras, assim como no som difratado por eles. O quarto problema trata da condução de calor na vizinhança de defeitos. Considerando que os defeitos são resultantes de uma adição ou remoção de porção de material, dando-se seguimento a uma relaxação elástica do meio, métricas efetivas do espaço perturbado pelo defeito são encontradas, com expressões semelhantes às obtidas pelo modelo análogo baseado no princípio de Fermat. Essas métricas geram um tensor condutividade térmica modificado, dando cabo ao estudo do campo de temperatura nessa situação. Mostramos que, dependendo dos valores da condutividade térmica perpendicular e paralela ao eixo de simetria da molécula líquido-cristalina e do defeito em questão, o gradiente de temperatura pode ser acentuado ou atenuado sobre o defeito, permitindo o controle da resposta térmica do material à temperatura, de acordo com a presença de defeitos. Suscitar um entendimento maior da física dos cristais líquidos e de seu emprego como background em modelos análogos de gravitação é o tema principal de cada um dos problemas analisados.
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Chia-LienMa and 馬嘉蓮. "Morphology and defect of cholesteric liquid crystal microdroplets suspending on microfibres." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/9rnu65.
Full textAbstract:
碩士國立成功大學
光電科學與工程學系
105
The orientation of liquid crystals (LC) and the formation of topological defects of LCs in confined geometries are determined by nematic elasticity, chirality, and surface anchoring. In this study, we report the deformations of the inner orientation in cholesteric LC (CLC) microdroplets with short- and long-pitch deposits on polymeric fibers. Two kinds of surface anchoring, namely, perpendicular anchoring at the air–CLC droplet interface and planar anchoring at the fiber–CLC droplet interface, coexist in this system. This thesis is divided into three parts. In the first part, we observed the equilibrium structures of the CLC microdroplets that were thermally cooled down from isotropic phase to chiral nematic phase. The alignment model of LC molecules under temperature change is proposed. The second and third parts of this study discuss the photo-dependent deformations of the azo-CLC microdroplets, which are composed of azo-LC-doped CLCs or azo-chiral-doped CLCs. UV irradiation-induced trans to cis isomerization of the azo-materials can disturb the orientations of the LCs and thus the isothermal phase transition or the pitch variations of the CLCs inside the microdroplets, resulting in inner deformations and alterations of the disclinations in the microdroplets. The photo-controlled deformations and defects of the CLC microdroplets on polymeric fibers presented in this work can not only be used to achieve topological remote control, but can also be applied in nanoscience and biomedical studies, as well as in developing devices based on topologically structured soft media.
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Wen, Chien How, and 簡浩文. "The Investigation of Defect Improving For Optically Compensated Bend Liquid Crystal Display." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/16262335039462422597.
Full textAbstract:
博士長庚大學
電子工程學系
99
Abstract OCB (Optically Compensated Bend) mode LCD has advantages in wide viewing angle and fast response time, and therefore can meet all LCDs' demands as the next generation display with perfect and high quality frame. However, in the OCB mode operating process, there are still essential problems to be overcome. The arrangement of liquid crystal molecules in cells are splayed in beginning, but it is operated in bend arrangement with fast responding. In topology, the turning phenomena of arrangements in splay and bend are not continuous. Therefore, there is a threshold voltage (VC) between these two states. This process needs some time to stabilize, and is called warm-up time. In this investigation, we used many newly invented processes, such as eximer laser, plasma, ion beam, double-structure, and high pretilt angle solve the warm-up time problem to OCB. The OCB advantages in fast response time have been preserved. We also compared with different new processes to reveal the best parameters ( Eximer laser 250±50mJ/cm2, Plasma 600mm/s, Ion beam 165ev, Double-structure and high pretilt angle 45。〜61。) for OCB research.
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Wang, Hsiao-Tsung, and 王筱从. "Ultralow-Threshold Lasing Based on a One-Dimensional Photonic Crystal Structure with a Liquid-Crystal Defect Layer." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/93272954465191813743.
Full textAbstract:
碩士國立交通大學
照明與能源光電研究所
102
In this thesis, a structure enabling enhancement of the local intensity of defect modes in the photonic bandgap is demonstrated by using asymmetric one-dimensional (1-D) photonic crystal (PC) with a liquid-crystal (LC) defect layer. The asymmetric PC structure consists of two multilayer substrates with overlapped bandgaps in the band edges. Owing to the high photon density of states at the photonic band edge, the resulting defect modes exhibit strong resonance in the overlapped region, giving a transmittance of five to ten times higher than that of a symmetric counterpart. Further, a comparison of the characteristics of defect-mode lasing was made between the asymmetric and symmetric 1D PC structures consisting of a dye-doped LC defect layer. We found that the lasing threshold of the asymmetric 1D PC structure to be twenty times lower than that of the symmetric one. The lasing peak can also be controlled by the applied voltage. Therefore, this asymmetric structure holds promise for high-power tunable PC lasers and high-contrast narrow band-pass filter. Besides, the central reflection wavelength can be tuned to the near-infrared region by modulating the optical thickness of the single layer coating in the multilayer for potential applications in tunable optical communication devices.
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Chuang, Chia-Tai, and 莊家泰. "The Improvement of Rubbing Process Defect of Thin-Film Transistor Liquid Crystal Display." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/10492034915265393581.
Full textAbstract:
碩士國立高雄第一科技大學
機械與自動化工程研究所
99
This is a case study to do improvements of Rubbing process Defect of TFT- ( Thin Film Transistor) Liquid Crystal Panel. It is a study on Rubbing process cloth supplies over run times improvement of defect and improves the quality for TFT-LCD Panel. The six sigma has many researches and case studies as an effective skill for a project improvement.The research follows six sigma “DMAIC” procedure using DOE(design of experiment) to analyze the defect of Rubbing Mura. Through the procedure of the research , the defect of yield decreases from “30.33~33.89%” to 0.%~0.5%.That is the defect and the quality of cell form from the rubbing process，is improvement dramatically.
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Lin, Chi-Wen, and 林淇文. "Alignment Defect Free Half-V Switching Mode Ferroelectric Liquid Crystal Devices and Their Applications." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/47392990190908482413.
Full textAbstract:
博士國立交通大學
光電工程學系
99
Many studies have confirmed that the fast response of surface-stabilized ferroelectric liquid crystal (SSFLC) is suitable for fast switching devices. However, the lack of a continuous gray scale limits the potential for display application. Half-V switching FLC mode (HV-FLC) with its intrinsic continuous gray scales is more suitable for the driving of active matrix thin-film-transistors (AM TFT). The major drawback in HV-FLC devices is the horizontal chevron alignment defect. This is due to the presence of both spontaneous polarization (PS) up and down domains when the HV-FLC device cools down from its N*-SmC* phase transition. Resolution of the alignment defect remains a challenge to overcome before the potential for display application of HV-FLC can be realized. In this dissertation, the origin of the horizontal chevron alignment defect is explained by considering the physical aspect of the FLC’s free energy. The PS up and PS down domains co-exist because of the same minimum total free energy in the symmetrical cell in which the top and the bottom alignment surfaces have the same polar surface interaction coefficients. As a result, a defect-free alignment texture is only achievable when the orientation of the FLC’s PS direction is the same. According to HV FLC’s total free energy, a large difference in the polar surface energy term under asymmetrical alignment conditions may hold the key to lowering the FLC’s free-energy level. Two approaches to solve the alignment problem caused by surface pre-treatment were identified. Firstly, by applying rubbing and plasma alignment techniques on both top and bottom substrates, the alignment strength which differentiates values were controlled. Secondly, by using alignment layers with opposite sign of surface polarities, the sign of was changed. The asymmetrical alignment techniques were applied to control the anchoring energy and surface polarity and to validate theoretical predictions. Using the asymmetric alignment technique, based on double-side striped electrodes, the electrically tunable FLC grating, approaching calculated diffraction efficiency is demonstrated. FLC’s alignment in the ITO patterned non-uniform surface is studied. The width of thin striped electrodes is designed smaller than half of the grating pitch to compensate for the fringe field effect and thus improve the diffraction efficiency. Good FLC alignment is able to be achieved by small cell gap, certain pitch design, and surface polarity control asymmetric cell. The remaining unsolved issue in display applications is the cell process limitation in manufacture. The cell gap of most TFT-LCDs is controlled larger than 3 µm. The minimum cell gap requirement is, at least, 2 times greater than SSFLC cell. We studied a potential approach which can be applied to minimize the alignment defects in the cell gap 3.5 µm.
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Wen, Jian-Zhi, and 溫健智. "Alignment Defect Free, Full Phase Modulation Ferroelectric Liquid Crystal Device and It’s Driving waveform." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/3cxu86.
Full textAbstract:
碩士國立交通大學
光電工程研究所
106
Many studies have confirmed that the fast response of surface-stabilized ferroelectric liquid crystal (SSFLC) is suitable for fast switching devices. However, the lack of a continuous gray scale limits the potential for display application. In order to get the continuously gray scale, we changed the input waveform to measure the R3206-50 cell E-O properties at 532 nm under 10 V and 10 Khz square wave. When we changed the square wave duty cycle from 50% to 90%, the HV-FLC cell E-O properties had also changed the transmittance corresponds to duty cycle continuously. The major drawback in HV-FLC devices is the horizontal chevron alignment defect. In the PVA-PI asymmetrical surface polarity hybrid cell, the layer structure of HV -FLC appeared in uniform direction and the horizontal chevron defects were completely suppressed After utilizing asymmetrical hybrid cell, contrast ratios and horizontal chevron defects of R3206–50 were greatly improved
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Tang, Wen-Cheng, and 湯文正. "Surface Defect Detection and Classification for Coating Brightness Enhancement Film in Liquid Crystal Display." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/nxhjut.
Full textAbstract:
碩士國立臺北科技大學
工業工程與管理系所
94
This paper develops an automatic optical inspection (AOI) system to inspect the surface defects such as Mura, bubble, streak, and contamination on Coating Brightness Enhancement Film (BEF). At first, using histogram equalization and local statistic parameter to enhance the contours of surface defects. Then, using the Otsu threshold method to segment the area of defect and obtain their locations and shapes of the defects. Once the location and shape of a surface defect is addressed, best fitting ellipse algorithm are utilized to extract the geometric features such as the number of the defective groups, area, length of major axis, length of minor axis, and the ratio calculated by the lengths of the major and minor axes. Finally, the back-propagation neural network, probabilistic neural network, and K-nearest neighbor method are used to classify the defect types. Experimental results have shown that the proposed method is able to achieve 100% identification rate by appropricate classification method and parameters.
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Lee, Ming-Jiu, and 李銘周. "Analysis and Classification of In-line Defect Inspection for Thin Film Transistor Liquid Crystal Display." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/45817767495209791135.
Full textAbstract:
碩士中原大學
機械工程研究所
96
Over the last decade, thin-film-transistor liquid-crystal-display (TFT-LCD), as display, has grown rapidly, and has almost replaced the market of cathode ray tube (CRT) monitor. The total value of photoelectric industry has exceeded the one of semiconductor. It has been a glaring industry that the government promotes actively. The manufacturing process of TFT-LCD, including array process, cell process and module assembly process, will be introduced in this technical report. Through the introduction, the importance of inline defect inspection in array process will be pointed out and detailed. In current practice, there are several equipments used for in-line inspection: automatic optical inspection (AOI) machine, micro-review machine, macro/micro machine, and critical-dimension overlap machine. These machines are used for inspecting various kinds of defects in different processes of the manufacturing. The defects are classified and analyzed according to the corresponding engineering. Therefore, the task of in-line inspection is able to enhance the yield rate and increase the business benefit. To achieve the goals of inspection efficiency, yield enhancement, and the production-cost reduction, the future works for inline inspection will be focused on automation and knowledge management. As for the inspection equipment, the key issues will be focused on several points, including how to enlarge the size of equipment, how to improve the accuracy of the measurement, and how to lift the efficiency. These are adapt to the large-size LCD panels, and are the future trends for the design of inspection equipment. In the final we will discuss the future works including the knowledge management and the automatic defect classification. In TFT-LCD manufacturing, there are some unknown defects actually. Due to unknown defects, a high and satisfactory defect classification rate can not be obtained. For solving this problem, it is necessary to develop a knowledge management system to improve the defect classification accuracy. In addition, several techniques, such as image processing, statistical texture extraction, data mining and neural network-based classification, can be used and integrated to achieve the goal of real-time defect recognition. The above-mentioned refers to the automatic defect-classification system.
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Kao, Hsiang-I., and 高祥益. "A Study on the recognition of defect patterns of ITO electrode lines of liquid crystal display." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/98679921248609614252.
Full textAbstract:
碩士國立高雄應用科技大學
機械與精密工程研究所
92
During the fabrication process of addressing electrodes on the ITO films that are deposited on the glass substrate of liquid crystal display, the electrode defects after lithography and etching, such as “open” and “short”, are usually found out through the use of pin-type detector. The defects are then classified and counted manually, which relies heavily on the expert experience. In this study the defect phenomena are investigated first, defect features and the related process factors are sorted out. For recognizing the LCD electrode defect, the method of moment invariant and backpropagation neural networks are applied.
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Chang, Yin-Hsien, and 張引獻. "A Study on Polyimide Process Improvement of Cell Form Defect for Liquid Crystal on Silicon Panel." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/20372975848445038419.
Full textAbstract:
碩士國立高雄第一科技大學
機械與自動化工程所
97
This is a case study to use six sigma skills do improvements on the LCoS (Liquid Crystal on Silicon) display industry. According to CES (Consumer Electronics Show) on 2009 , domestic and foreign well-known research institution as digitimes and TSR(Techno System Research) reveal to the investigation result of the technical application products of mini-projection, the technological development potentiality of the miniature projection is great. Therefore can know development and improvement of mini-projection is lasting and necessary. In order to make famous in mini-projection technology for LCoS. And it is a study on polyimide process improvement of defect and improves the quality of the projection image for LCoS Panel. The six sigma had been proved by many researches and case studies as an effective skill for a project improvement. The research follows six sigma “DMAIC” procedure to use DOE(design of experiment) to analyze the defect of polyimide for LCoS. And it concludes through the procedure of the research, we can improve the defect of cell form for polyimide process and improves the quality of the projection image. Give the best parameters standardization and release to the procedure of manufacture, improves the cell form defect in an all-round way.