Liquid Crystal Display Modes in a Nontilted Bent-Core Biaxial Smectic Liquid Crystal

Liquid crystal display (LCD) modes associated with the rotation of the secondary director in nontilted, biaxial smectic phase of an achiral bent-core compound are demonstrated. For LCDs, we find that at least four display modes are possible using SmAPA phase of the studied material, in which the minor directors in adjacent layers are aligned antiferroelectrically. The advantages of these modes include low driving field (1–2 V/ µm), high contrast ratio 1000:1, relatively fast switching time of 0.5 ms and continuous gray scale. The molecular short axis or the polar axis in a negative dielectric, biaxial material is oriented by the in-plane electric field by a combination dielectric biaxiality and polarity at low electric fields and polarity at higher fields

Evaluation of Electro-Optic Behaviour of Chiral Smetic Liquid Crystals Dispalys with V-shaped response

In the last years, chiral smectic liquid crystals with V-shaped electro-optic response have been reported as one of the most promising technologies for display applications. In this work,some experiments have been made in order to check electrooptical performance of this kind of materials. Particularly, frequency dependence of optical response and memory effect in transmission have been analyzed. Microscopic observations of intermediate transmission levels and measurements of apparent tilt angle and response time have been also carried out

Functional bent-core liquid crystals studied through second harmonic generation and X-ray diffraction

110 p.Los moléculas mesógenas con forma de banana (bent-core) dan lugar a nuevas fases cristal líquido con diversas funcionalidades de interés en aplicaciones tecnológicas. En esta tesis se han estudiado y caracterizado nuevos materiales tipo banana mediante microscopía óptica de polarización, generación de segundo armónico y rayos X. Más específicamente, los principales puntos desarrollados en este trabajo han sido los siguientes: Se han investigado las propiedades ópticas no lineales de dos nuevos materi mesógenos diseñados específicamente para este tipo de aplicación, uno tipo banana y otro con forma de H. Las eficiencias encontradas para el proceso de generación de segundo armónico son las más altas entre las publicadas hasta ahora para esta clase de materiales. Se ha estudiado en profundidad la transición de fase B1(columnar)-82(lamelar) mediante difracción de rayos X en muestras alineadas. A partir de los resultados hemos presentado un mecanismo que explica la sorprendentemente baja entalpía de transición y hemos propuesto una modificación para la estructura de la fase columnar. Por otro lado hemos deducido una nueva estructura antiferroeléctica local para la llamada fase B4 mediante el análisis del diagrama completo de rayos X. Asimismo, un material con una fase esméctica ópticamente isótropa es estudiado y se establece el tipo de razones que originan la formación de dicha estructura. Finalmente, y a partir de las propiedades observadas en algunos de los materiales estudiados, se proponen dos nuevas funcionalidades para estos mesógenos: fotoconductividad en compuestos con grupos TTF y un nuevo modo de operación LCD utllizando fases esmécticas y ópticamente isótropas

Grating Aligned Ferroelectric Liquid Crystal Devices

This thesis is concerned with the vertical grating alignment of ferroelectric liquid crystals (FLCs). FLCs exhibit fast electro-optic response times compared to traditional nematic devices, and so are of particular interest for use in micro-displays and liquid crystal on silicon (LCoS) spatial light modulators. Unfortunately such materials are highly susceptible to shock induced ow. This work introduces the VGA-FLC device geometry: a vertical grating aligned ferroelectric liquid crystal display. The vertical alignment gives preferential alignment to the smectic layers, and the amplitude and pitch of the grating ensure stable alignment of the c-director of the FLC. The combined effect is shown to result in a shock-stable FLC geometry. The device is addressed with in-plane electric fields, and is shown to obtain fast optical response times. The theory and physics of the device is explored, and further experiments are suggested that can be performed for device optimisation

Flexible glass substrates with via holes for TFT backplanes

This paper looks at flexible glass substrates with via holes for TFT backplane

Field-Orientation Coupling Effects in Nematic Liquid Crystal Cells

Using the continuum Landau-de Gennes model for the nematic liquid crystal (NLC) phase, we study the equilibrium behaviour of nematic cells, accounting for the coupling between external fields and nematic order. This is motivated by the substantial past theoretical and computational studies either neglecting or simplifying this coupling. Two different types of NLC cells are studied, those used to measure nematic elasticity through observation of a macroscopic optical response (Freedericksz transition) and a typical NLC light shutter used in liquid crystal display (LCD) technology. The Freedericksz cell and its associated transition are studied, comparing simulation prediction, given phenomenological parameters describing nematic elasticity, to experimental observations. This NLC cell configuration involves a relatively simple imposed electric (or magnetic) field, which is usually approximated instead of numerically determined. Particular emphasis is placed on investigating the impact of typical model approximations and parameter variance on the predicted transition point. We demonstrate that the relative values of the thermodynamic bulk constants has a pronounced effect on the transition voltage. It is shown that the coupling effect becomes significant above the Freedericksz transition point. The in-plane switching (IPS) nematic cell is studied, which involves a relatively complex electric field compared to the previous case. Approximation of the electric field is not feasible in this case, highlighting the use of a fully-coupled simulation approach. The effects of electrode placement and use of a fully coupled model versus a decoupled isotropic approximation are studied. A significant discrepancy between the predicted ON-state textures near the lower substrate of the IPS cells between the coupled and uncoupled models is observed. Finally, the utility of the model for the design and optimization of LCD cell systems is demonstrated and discussed

Properties of the Broad-Range Nematic Phase of a Laterally Linked H-Shaped Liquid Crystal Dimer

In search for novel nematic materials, a laterally linked H-shaped liquid crystal dimer have been synthesized and characterized. The distinct feature of the material is a very broad temperature range (about 50 oC) of the nematic phase, which is in contrast with other reported H-dimers that show predominantly smectic phases. The material exhibits interesting textural features at the scale of nanometers (presence of smectic clusters) and at the macroscopic scales. Namely, at a certain temperature, the flat samples of the material show occurrence of domain walls. These domain walls are caused by the surface anchoring transition and separate regions with differently tilted director. Both above and below this transition temperature the material represents a uniaxial nematic, as confirmed by the studies of defects in flat samples and samples with colloidal inclusions, freely suspended drops, X-ray diffraction and transmission electron microscopy.Comment: 30 pages (including Supplementary Information), 7 Figure

Studies of the effect of structural variation on Mesomorphic Characteristics in Thermotropic Mesogenes

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