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Dissertations / Theses on the topic 'Liquid crystal'
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1
Legge, Coulton Heath. "Structural modifications in liquid crystals and liquid crystal polymers." Thesis, University of Reading, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306164.
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Wu, Haixia. "Anchoring Behavior of Chiral Liquid Crystal at Polymer Surface: In Polymer Dispersed Chiral Liquid Crystal Films." Thesis, Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-04082004-154054/unrestricted/wu%5Fhaixia%5F200405%5Fmast.pdf.
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Thesis (M.S.)--Textile and Fiber Engineering, Georgia Institute of Technology, 2004.Griffin, Anselm, Committee Member; Srinivasarao, Mohan, Committee Chair; Park, Jung O., Committee Member. Includes bibliographical references (leaves 101-105).
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Cosquer, Guirec Yann. "Liquid crystals with novel terminal chains as ferroelectric liquid crystal hosts." Thesis, University of Hull, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322457.
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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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Ford, A. D. "Liquid crystal lasers." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599106.
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This thesis examines the emission properties of liquid crystal (LC) lasers. The aim is to investigate correlations between the emission properties of the laser, in particular the threshold energy and the slope efficiency, and the macroscopic physical properties of the liquid crystal host. Using the threshold gain term obtained for a distributed feedback laser in the context of the coupled mode theory, an expression for the threshold energy (Eth) is obtained, in the form Eth ∝ d + 1/Δn²d² where d is the cell thickness and Δn is the birefringence. The slope efficiency is considered to be inversely proportional to the threshold energy and thus the laser emission properties are evaluated in the context of the host physical parameters. These relationships provide fits that are in good agreement with experimental data for the threshold energy and slope efficiency dependence on cell thickness. It is shown theoretically that a threshold-less laser can be achieved for large cell thicknesses if the absorption losses are neglected. For a given cell thickness, the emission properties from a range of monomesogens, nematogen mixtures and bimesogens provide evidence that LCs with high birefringence give rise to a low threshold energy. This is in accordance with the above expression. However, examining the emission properties of a high birefringence LC laser, suggest that a high birefringence does not necessarily give rise to high slope efficiency. The slope efficiency is shown to follow the relation, ηs = P₃/Eth where P3 depends on parameters such as saturation intensity and addition loss mechanisms. One possible loss mechanism highlighted in this thesis is associated to the elastic moduli of the host LC. This parameter provides an indication of the structural integrity of the helical structure of the LC host. The bimesogen with the largest elastic moduli gives rise to a slope efficiency of 20%. In addition to the chiral nematic phase providing the host structure for the band edge laser, the emission properties from three addition LC lasers, using alternative LC phase is also shown; the one dimensional chiral smectic C phase, the three dimensional blue phase I and the random laser that utilises the high scattering texture of the smectic A phase.
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Kirby, Neil Andrew. "Liquid crystal polymers." Thesis, University of Sussex, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240445.
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Higgenbottom, Morris Scott. "Liquid crystal modulation of retroreflection : a low-power communication/location technology." Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/16695.
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Liu, Zhijian. "Photo-aligned LC cell with weak anchoring energy and specific profiles : physics & applications /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?ECED%202006%20LIU.
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Reznikov, Dmytro. "Effect of surface alignment layer on electro-optical properties of ferroelectric liquid crystal displays." [Kent, Ohio] : Kent State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1227562895.
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Thesis (Ph.D.)--Kent State University, 2008.Title from PDF t.p. (viewed Jan 5, 2010). Advisor: Philip J. Bos. Keywords: liquid crystal, smectic, display, ferroelectric. Includes bibliographical references (p. 190-194).
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Dong, Shaosheng. "Liquid Crystal Polymers And Dendritic Liquid Crystals: Synthesis, Morphology, Rheology And Binary Mixtures." online version, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1094584392.
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Fan, Yun-Hsing. "TUNABLE LIQUID CRYSTAL PHOTONIC DEVICES." Doctoral diss., University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3926.
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Liquid crystal (LC)-based adaptive optics are important for information processing, optical interconnections, photonics, integrated optics, and optical communications due to their tunable optical properties. In this dissertation, we describe novel liquid crystal photonic devices and their fabrication methods. The devices presented include inhomogeneous polymer-dispersed liquid crystal (PDLC), polymer network liquid crystals (PNLC) and phase-separated composite film (PSCOF). Liquid crystal/polymer composites could exist in different forms depending on the fabrication conditions. In Chap. 3, we demonstrate a novel nanoscale PDLC device that has inhomogeneous droplet size distribution. In such a PDLC, the inhomogeneous droplet size distribution is obtained by exposing the LC/monomer with a non-uniform ultraviolet (UV) light. An electrically tunable-efficiency Fresnel lens is devised for the first time using nanoscale PDLC. The tunable Fresnel lens is very desirable to eliminate the need of external spatial light modulator. Different gradient profiles are obtained by using different photomasks. The nanoscale LC droplets are randomly distributed within the polymer matrix, so that the devices are polarization independent and exhibit a fast response time. Because of the small droplet sizes, the operating voltage is higher than 100 Vrms. To lower the driving voltage, in Chap. 2 and Chap. 3, we have investigated a polymer-network liquid crystal (PNLC) using a rod-like monomer structure. Since the monomer concentration is only about 5%, the operating voltage is below 10 Vrms. The PNLC devices are polarization dependent. To overcome this shortcoming, stacking two cells with orthogonal alignment directions is a possibility. In Chap. 3, another approach to lower the operating voltage is to use phase-separated composite film (PSCOF) where the LC and polymer are separated completely to form two layers. Without multi-domain formed in the LC cell, PSCOF is free from light scattering. Using PNLC and PSCOF, we also demonstrated LC blazed grating and Fresnel lens. The diffraction efficiency of these devices is continuously controlled by the electric field. Besides Fresnel lens, another critical need for imaging and display is to develop a system with continuously tunable focal length. A conventional zooming system controls the lens distance by mechanical motion along the optical axis. This mechanical zooming system is bulky and power hungry. To overcome the bulkiness, in Chap. 4 we developed an electrically tunable-focus flat LC spherical lens which consists of a spherical electrode imbedded in the top flat substrates while a planar electrode on the bottom substrate. The electric field from the spherical and planar electrodes induces a centrosymmetric gradient refractive index distribution within the LC layer which, in turn, causes the focusing effect. The focal length is tunable by the applied voltage. A tunable range from 0.6 m to infinity is achieved. Microlens array is an attractive device for optical communications and projection displays. In Chap. 5, we describe a LC microlens array whose focal length can be switched from positive to negative or vise versa by the applied voltage. The top spherical electrode glass substrate is flattened with a polymer layer. The top convex substrate and LC layer work together like a zoom lens. By tuning the refractive index profile of the LC layer, the focal length of the microlens array can be switched from positive to negative or vise versa. The tunable LC microlens array would be a great replacement of a conventional microlens array which can be moved by mechanical elements. The fast response time feature of our LC microlens array will be very helpful in developing 3-D animated images. A special feature for LC/polymer composites is light scattering. The concept is analogous to the light scattering of clouds which consist of water droplets. In Chap. 6, we demonstrate polymer network liquid crystals for switchable polarizers and optical shutters. The PNLC can present anisotropic or isotropic light scattering behavior depending on the fabrication methods. The use of dual-frequency liquid crystal and special driving scheme leads to a sub-millisecond response time. The applications for display, light shutters, and switchable windows are emphasized. Although polymer networks help to reduce liquid crystal response time, they tend to scatter light. In Chap. 7, for the first time, we demonstrate a fast-response and scattering-free homogeneously-aligned PNLC light modulator. Light scattering in the near-infrared region is suppressed by optimizing the polymer concentration such that the network domain sizes are smaller than the wavelength. As a result, the PNLC response time is ~300X faster than that of a pure LC mixture except that the threshold voltage is increased by ~25X. The PNLC cell also holds promise for mid and long infrared applications where response time is a critical issue.Ph.D.
Other
Optics and Photonics
Optics
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Kim, Sang Hwa. "Fast Switching Polymer Stabilized Liquid Crystal Devices: Morphological and Electro-Optical Properties." [Kent, Ohio] : Kent State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1101220722.
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Tadeusiak, Andrezej Jan. "Fluorinated liquid crystal systems." Thesis, Durham University, 2008. http://etheses.dur.ac.uk/2259/.
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Chapter 1. An introduction to the principles of two different types of LC cell and the design of new fluorinated materials for modem LCD applications is presented here. Discussion includes reasons why fluorinated molecules have become the compounds of choice for display devices, and a history of organo-fluorine chemistry from early discovery of the element, through nucleophilic substitution and debromolithiation reactions of bromoperfluorobenzenes, to very recent developments in synthesis.Chapter 2. This chapter presents a brief overview of some of our early ideas as to how new fluorinated LCs might be made synthetically, exploiting advances in the field of organo-fluorine chemistry, utilising perfluorobenzene and bromoperfluorobenzene "scaffolds."Chapter 3. A discussion of how new "model" fluorinated LC materials were obtained via nucleophilic aromatic substitution in bromoperfluorobenzenes is presented in this chapter. The flexibility of the methodology is demonstrated through use of different substrate isomers to afford different aromatic fluorination patterns, and of different nucleophiles to create "families" of homologous materials.Chapter 4. The versatility of bromoperfluorobenzenes as substrates is exemplified in this chapter, whereby a number of isomers of these "scaffold" molecules were built upon via debromolithiation followed by reaction with electrophiles. This methodology was also applied to functionalised bromofluorobenzenes from chapter 3, and a small library of related compounds was synthesised as in the previous chapter.Chapter 5. Recent advances in metal C-F bond activation have assisted with ourdevelopment of a new synthetic route to fluorobiphenyl moieties, based on Suzuki- Miyaura chemistry and presented in this chapter.Chapter 6. Many of the novel fluorinated materials synthesised in chapters 3 to 4 were sent to SONY MSL, Stuttgart, and their properties determined by tests including electro- optical, DSC, and VHR analysis. The results are discussed and compared, and their potential for application in current LC display devices assessed.
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Draper, Michael. "Golden liquid crystal nanoparticles." Thesis, University of York, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542804.
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Verrall, Mark Andrew. "Ferroelectric liquid crystal polymers." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313194.
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Springle, Ian David. "Photoluminescent liquid crystal displays." Thesis, University of Cambridge, 1997. https://www.repository.cam.ac.uk/handle/1810/272071.
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Xu, Peizhi. "Electrooptical modes of liquid crystal for shutter and display applications /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202005%20XU.
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Zhang, Zichen. "Phase-only nematic liquid crystal on silicon devices." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610052.
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Burnham, Kikue Sugiyama. "Phototriggers for a liquid crystal-based optical switch." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/27900.
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Yeung, Fion Sze Yan. "Variable liquid crystal pretilt angles by nanostructured surfaces and their applications /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?ECED%202007%20YEUNG.
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Du, Tao. "Single cell gap transflective liquid crystal displays and the use of photoalignment technology /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?ECED%202009%20DU.
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Li, Xihua. "Bi and multi stable ferroelectric liquid crystal displays /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?ECED%202008%20LI.
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Zhou, Ying. "CHOLESTERIC LIQUID CRYSTAL PHOTONIC CRYSTAL LASERS AND PHOTONIC DEVICES." Doctoral diss., University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2706.
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This dissertation discusses cholesteric liquid crystals (CLCs) and polymers based photonic devices including one-dimensional (1D) photonic crystal lasers and broadband circular polarizers. CLCs showing unique self-organized chiral structures have been widely used in bistable displays, flexible displays, and reflectors. However, the photonic band gap they exhibit opens a new way for generating laser light at the photonic band edge (PBE) or inside the band gap. When doped with an emissive laser dye, cholesteric liquid crystals provide distributed feedback so that mirrorless lasing is hence possible. Due to the limited surface anchoring, the thickness of gain medium and feedback length is tens of micrometers. Therefore lasing efficiency is quite limited and laser beam is highly divergent. To meet the challenges, we demonstrated several new methods to enhance the laser emission while reducing the beam divergence from a cholesteric liquid crystal laser. Enhanced laser emission is demonstrated by incorporating a single external CLC reflector as a polarization conserved reflector. Because the distributed feedback from the active layer is polarization selective, a CLC reflector preserves the original polarization of the reflected light and a further stimulated amplification ensues. As a result of virtually doubled feedback length, the output is dramatically enhanced in the same circular polarization state. Meanwhile, the laser beam divergence is dramatically reduced due to the increased cavity length from micrometer to millimeter scale. Enhanced laser emission is also demonstrated by the in-cell metallic reflector because the active layer is pumped twice. Unlike a CLC reflector, the output from a mirror-reflected CLC laser is linearly polarized as a result of coherent superposition of two orthogonal circular polarization states. The output linear polarization direction can be well controlled and fine tuned by varying the operating temperature and cell gap. Enhanced laser emission is further demonstrated in a hybrid photonic band edge - Fabry-Perot (FP) type structure by sandwiching the CLC active layer within a circular polarized resonator consisting of two CLC reflectors. The resonator generates multiple FP modes while preserving the PBE mode from the active layer. More importantly this band edge mode can be greatly enhanced by the external resonator under some conditions. Theoretical analysis is conducted based on 4×4 transfer matrix and scattering matrix and the results are consistent with our experimental observations. To make the CLC laser more compact and miniaturized, we have developed a flexible polymer laser using dye-doped cholesteric polymeric films. By stacking the mirror reflecting layer, the active layer and the CLC reflecting layer, enhanced laser emission was observed in opposite-handed circular polarization state, because of the light recycling effect. On the other hand, we use the stacked cholesteric liquid crystal films, or the cholesteric liquid crystals and polymer composite films to demonstrate the single film broadband circular polarizers, which are helpful for converting a randomly polarized light into linear polarization. New fabrication methods are proposed and the circular polarizers cover ~280 nm in the visible spectral range. Both theoretical simulation and experimental results are presented with a good match.Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD
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Bin, Peng. "Liquid crystal polymer brushes and their application as alignment layers in liquid crystal cells." [S.l. : s.n.], 2000. http://ArchiMeD.uni-mainz.de/pub/2000/0094/diss.pdf.
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DEY, SONAL. "ELASTICITY OF MAIN CHAIN LIQUID CRYSTAL ELASTOMERS AND ITS RELATIONSHIP TO LIQUID CRYSTAL MICROSTRUCTURE." Kent State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=kent1385403238.
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Neupane, Krishna Prasad. "Light Scattering Studies of Orientational Order in Liquid Crystalline Tetrapodes and Lyotropic Chromonic Liquid Crystals." Kent State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=kent1239811255.
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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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Shi, Lei. "Tunable liquid crystal polarization gratings." [Kent, Ohio] : Kent State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1258988951.
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Thesis (Ph.D.)--Kent State University, 2009.Title from PDF t.p. (viewed Apr. 22, 2010). Advisor: Philip Bos. Keywords: Liquid crystal; beam steering; polarization gratings; diffraction efficiency; decentered microlens array. Includes bibliographical references (p. 216-219).
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Shafran, Matthew S. "Responsive liquid crystal polymer rods." Morgantown, W. Va. : [West Virginia University Libraries], 2008. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5598.
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Thesis (M.S.)--West Virginia University, 2008.Title from document title page. Document formatted into pages; contains viii, 71 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 63-67).
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Walker, David B. "Ferroelectric liquid crystal waveguide modulators." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/13277.
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Lee, Michael Siew Khay. "Side chain liquid crystal polysiloxanes." Thesis, University of Hull, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384846.
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Gillespie, C. "Dye doped liquid crystal lasers." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599422.
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This thesis examines the emission properties of dye-doped liquid crystal lasers, which are of interest because they have the potential to provide compact, low threshold, tunable laser sources for applications ranging from medicine to displays. The primary aim is to provide the first detailed study of the interactions between liquid crystals (LCs) and laser dyes and to examine their effect upon the emission properties of dye-doped liquid crystal lasers. Five different dyes are examined and, in all cases, the LC host (a nematic mixture, E49) is shown to have a significant effect upon the properties of the dye, through a combination of general and specific solvent-solute interactions. Lasing is demonstrated from all five dyes in the chiral nematic (N*) mesophase. Conventional xanthene laser dyes, rhodamine 6G chloride and rhodamine B chloride, are shown to be unsuitable for N*LC lasers because their ionic nature and isotropic molecular shapes limit their solubility in LC materials. Emission is shown to occur preferentially at the long wavelength reflection band edge for small degrees of alignment of the dye in the LC host. Three elongated laser dyes (DCM, PM597 and PM580) are shown to be more compatible with E49. N*LC laser samples were made using dye concentrations in the range 0.5 wt% to 2.0 wt%. For each dye, slope efficiency (ηs) values were used to calculate relative quantum efficiency values, which decreased linearly as the concentration increased. ηs is shown to peak at a characteristic value corresponding to the balance between increasing absorbance and decreasing quantum efficiency with increasing dye concentration. The largest ηs demonstrated is 32%, which corresponds to 1.0 wt% PM597. The Eth of both PM597 and PM580 is shown to increase linearly with increasing concentration, whereas the Eth of DCM shows the opposite tendency. It is proposed that the different Eth trends indicate different quantum efficiency quenching mechanisms. Lasing was demonstrated from novel bimesogenic mixtures that showed wide temperature range blue phase I* (BP I*) mesophases. The preparation and properties of the BP I* samples are described. the nature of the laser emission is shown to depend upon the input energy used. For low inputs energies (<~ 3μJ/pulse), multimode lasing is demonstrated from the BP I* texture, whereas for high input energies (> ~ 3 μJ/pulse) random lasing is demonstrated from optically induced focal conic (N*) textures in the BP I* samples.
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Kim, Wook Sung. "Scattering in liquid crystal displays." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526470.
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Wu, Yung-Hsun. "FAST RESPONSE LIQUID CRYSTAL DEVICES." Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3111.
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Liquid crystal (LC) has been widely used for displays, spatial light modulators, variable optical attenuators (VOAs) and other tunable photonic devices. The response time of these devices is mainly determined by the employed liquid crystal material. How to obtain fast response for the LC devices is a fundamentally important and technically challenging task. In this dissertation, we investigate several methods to improve liquid crystal response time, for examples, using dual-frequency liquid crystals, polymer stabilized liquid crystals, and sheared polymer network liquid crystals. We discover a new class of material, denoted as sheared polymer network liquid crystal (SPNLC) which exhibits a submillisecond response time. First, dual-frequency liquid crystals and polymer network methods are demonstrated as examples for the variable optical attenuators. Variable optical attenuator (VOA) is a key component in optical communications. Especially, the sheared PNLC VOA shows the best result; its dynamic range reaches 43 dB while the response time is in the submillisecond range at 1550 nm wavelength, which is 50 times faster than the commercial LC-based VOA. Second, we report a new device called axially-symmetric sheared polymer network liquid crystals (AS-SPNLC) and use it as LC devices. An axially-symmetric sheared polymer network liquid crystal has several attractive features: 1) it is polarization independent, 2) it has gradient phase change, and 3) its response time is fast. It can be used for polarization converter and divergent LC lens. In addition, a new method for simultaneously measuring the phase retardation and optic axis of a compensation film is demonstrated using an axially-symmetric sheared polymer network liquid crystal. This simple technique can be used for simultaneously measuring the optic axis and phase retardations of both A- and C-plates. These compensation films have been used extensively in wide-view LCD industry. Therefore, this method will make an important impact to the LCD industry.Ph.D.
Optics and Photonics
Optics
35
Lin, Yi-Hsin. "POLARIZATION-INDEPENDENT LIQUID CRYSTAL DEVICES." Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4199.
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Liquid crystal (LC) devices can be operated as amplitude modulators and phase modulators. LC amplitude modulation is commonly used in liquid crystal display (LCD) while phase-only modulation is useful for laser beam steering, tunable grating, prism, lens, and other photonic devices. Most LC devices are polarization dependent and require at least one polarizer. As a result, the optical efficiency is low. To enhance display brightness, a power hungry backlight has to be used leading to a high power consumption and short battery life. In a LC phase modulator, the polarization dependent property complicates the laser beam steering system. It is highly desirable to develop new operating mechanisms that are independent of the incident light polarization. In this dissertation, we have developed eight polarization-independent liquid crystal operation principles: three of them are aimed for displays and the other five are for phase modulators. For amplitude modulations, a new polymer-dispersed liquid crystal (PDLC) and two new dye-doped LC gels are polarizer-free by combining light scattering with dye-absorption effects. In phase modulation, we explore five device concepts: PDLC and Polymer-Stabilized Cholesteric Texture (PSCT), homeotropic LC gels, thin polymer film separated double-layered structure, and double-layered LC gels. In the low voltage regime, both PDLC and PSCT have a strong light scattering. However, as the voltage exceeds a certain level, the phase modulation is scattering-free and is independent of polarization. The homeotropic LC gels do not require any biased voltage and the response time is still fast. Although the remaining phase in these devices is small, they are still useful for micro-photonic device applications. To increase the phase change, thin polymer film separated double-layered structure is a solution. The orthogonal arrangement of top and bottom LC directors results in polarization independence. However, the response time is slow. Similarly, double-layered LC gels are not only polarization independent but also fast response due to the established polymer network.Ph.D.
Optics and Photonics
Optics
36
Jiao, Meizi. "Fast-response liquid crystal displays." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4580.
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After about five decades of extensive material research and device development, followed by massive investment in manufacturing technology, thin-film-transistor liquid-crystal-display (TFT-LCD) has finally become the dominant flat panel display technology. Nowadays, LCD performances, such as viewing angle, contrast ratio, and resolution, have reached acceptable levels. The remaining major technical challenges are response time, light efficiency, and sunlight readability. Fast response time is desired to reduce motion blur and to enable field sequential color displays using red (R), green (G), and blue (B) LEDs (light emitting diodes) without noticeable color breakup. Sequential RGB colors would eliminate the commonly used spatial color filters which in turn enhances light efficiency and resolution density by ~ 3X. In this dissertation, several new approaches for achieving fast-response LCDs are explored. From material viewpoint, the most straightforward approach for achieving fast response time is to employ a thin cell gap with high birefringence and low viscosity liquid crystal (LC). We investigated the thin cell approach theoretically and experimentally. Voltage shielding effect and anchoring energy effect of alignment layers are found to play important roles on operating voltage and response time. Simulations are carried out to understand the underlying physics and confirm the experimental results quantitatively. Another approach to realize fast response time is to explore novel device configuration. Here, we proposed a dual fringing-field switching (DFFS) mode in which small LC domains are formed following the distribution of fringing fields. Therefore, it exhibits submillisecond response time without using thin cell or overdrive/undershoot voltage method. The response time of the DFFS mode is ~20X faster than a conventional vertical aligned LCD.; In addition, high optical efficiency is achieved from the complementary top and bottom active LC domains. Two transmissive and one transflective LCDs using DFFS mode are conceived and their electro-optical properties investigated. A shortcoming of DFFS LCDs is their fabrication complexity. To keep the advantages of this fast-response mode while avoiding the requirement of double-TFTs and pixel registration, we modified the device structure to transflective LCD which uses a single TFT in each pixel and vertical aligned positive dielectric anisotropy LC. Two types of electrodes are considered: fringing-field switching (FFS) and in-plane switching (IPS). Besides fast response time and high transmittance, such a transflective LCD shows good sunlight readability. As nematic LC is gradually approaching to its limit in term of response time, polymer-stabilized blue phase (PSBP) LCD is emerging. It has potential to become next-generation display because of following revolutionary features: submillisecond response time, no need for alignment layer, good dark state and symmetric viewing angle, and cell gap insensitivity if IPS electrode is employed. In this dissertation, we studied the material-property correlation of Kerr effect-induced birefringence in nano-structured PSBP LC composites. Furthermore, a new device configuration of BP LCD with corrugated electrodes is proposed to solve two critical technical issues: high driving voltage and relatively low transmittance. The on-state voltage can be reduced from ~35 Vsubscript rms] to ~10 Vsubscript rms] which will enable TFT addressing, and the transmittance is improved from ~65% to ~85%. This new device configuration will accelerate the emergence of PSBP LCD. Wide view is another important requirement for a high-end display. Several new LCD configurations with negative A-plate and biaxial plate as phase compensation films are proposed to achieve wide view and broadband operation.; The underlying working principles are studied and detailed display performances are included in this dissertation.ID: 030422960; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 114-122).
Ph.D.
Doctorate
Optics and Photonics
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Blatch, Andrew. "Non-symmetric liquid crystal dimers." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246224.
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Pawsey, Anne Claire. "Colloids at liquid crystal interfaces." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/8969.
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This thesis presents a study of colloidal particles dispersed in thermotropic liquid crystals. It has a specific focus on colloids in the presence of an interface between the liquid crystal and an isotropic fluid. Three systems are studied: colloids trapped at a planar interface between a cholesteric liquid crystal (CLC) and an isotropic oil, nematic emulsions with interfacial colloids and the influence of colloids on the phase transition kinetics of the cholesteric blue phase. Experiments are carried out using polarising optical and confocal microscopy. By combining these techniques, the director field of the liquid crystals could be imaged in combination with precise observation of the colloid locations. Custom image analysis algorithms are developed to extract the information. In the first system, we create an interface between a cholesteric liquid crystal and an isotropic liquid. Homeotropic anchoring leads to a well aligned cholesteric layer and the formation of the fingerprint texture. Fluorescent colloidal particles with planar surface anchoring are dispersed in the CLC. A majority of these particles decorate the interface. The final distribution of particles perpendicular to the interface has a clear dependence on the particle size. In the plane of the interface, surface defects form a template for the colloids. The second system is a particle dispersion within a short pitch CLC which exhibits a blue phase. The colloidal particles and associated defects act as nucleation sites for the blue phase in the cholesteric to blue phase transition. Colloidal particles cause localised melting from the blue phase to the isotropic phase and lead to a larger temperature range for coexistence between isotropic and blue phases. Furthermore, the isotropic regions can be faceted, their shape and size is controlled by the blue phase elasticity. In the final system, a nematic emulsion is created. Droplets of nematic LC are dispersed in water. Colloidal particles initially mixed into the liquid crystal decorate the interface between the two fluids. The addition of a surfactant switches the liquid crystal alignment at the fluid-fluid interface from planar to homeotropic. This forces a change in defect structure, from two boojums at the poles to a hedgehog defect in the droplet centre. The presence of colloids affects the switching dynamics and alters the final liquid crystal alignment preventing the droplets from forming a central radial defect. There is a symbiotic relationship between the particle properties - size and anchoring at the surface - and the elastic properties of the liquid crystal in the bulk and in the presence of an interface with an isotropic fluid. How the systems respond when the balance of these factors is altered is explored throughout the thesis.
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Everitt, David R. R. "Cyclic polymer liquid crystal structures." Thesis, Sheffield Hallam University, 1990. http://shura.shu.ac.uk/19634/.
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Recent advances in liquid crystal research have included the synthesis of polymeric materials which contain liquid crystalline moieties. The work presented here concerns the study of the structure-property relationships of a particular group of liquid crystalline polymers in which the polymer backbone is cyclic, with the mesogenic moieties attached as side-chains. We have observed mesogenic phases above room temperature for materials comprising cyclic poly(dimethylsiloxane) backbones with mesogenic moieties attached by alkyl spacer units. Dielectric relaxations have been observed in the mesophases of these materials and the activation energies and extent of broadening of the relaxations have been related to the physicalstructure of the molecules. Theoretical studies have been undertaken by the use of the Metropolis Monte Carlo technique and a mean field calculation. Two models have been studied by the Monte Carlo technique in the NVT ensemble. In the first, each complete molecule was represented by a disc-like interactions potential and a tendency for the molecules to align in columns was revealed at low temperature and high density. In the second model, each mesogenic unit was represented separately, with the cyclic polymerrepresented as a constraint on the relative motions of the attached mesogens. A variety of liquid crystalline phases, from discotic nematic to calamitic nematic, were observed at low temperature as the coupling between the side-chains and the backbones was adjusted. In the mean field model energy terms were included for ring-ring interactions, mesogen-mesogen interactions and the coupling between the mesogenic moieties and the backbones. The uniaxial solution of this model also showed a shift from calamitic nematic to discoticnematic phases as the strength of the coupling was increased. Comparisons of the results of the models and the physical measurements are presented and suggestions for future work are proposed.
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Venkataraman, Nithya Leela. "Photosensitive Cholesteric Liquid Crystal Materials." Kent State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=kent1248110797.
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Lazo-Martinez, Israel Esteban. "Liquid Crystal Enabled Electrokinetic Phenomena." Kent State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=kent1397725003.
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Gimenez, Pinto Vianney Karina. "MODELING LIQUID CRYSTAL POLYMERIC DEVICES." Kent State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=kent1398039813.
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Li, Yuet Wing. "Liquid crystal pretilt angle measurement /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202003%20LIY.
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Mang, Xiaobin. "Self-assembled liquid crystal nanostructures." Thesis, University of Sheffield, 2012. http://etheses.whiterose.ac.uk/2041/.
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Self-assembly of liquid crystalline molecules has been a highly interesting research area over the past few decades. The modification of traditional rod-like liquid crystalline molecules by adding additional functional groups is an effective way to obtain novel liquid crystal phases due to the segregation of incompatible molecular components, and this has been proved by various mesophases obtained from molecules which possess special shapes and structures. More recently, liquid crystalline molecules have been introduced to functionalize metallic nanoparticles to arrange these spherical particles into ordered structures. In this case, liquid crystalline molecules are grafted onto the surfaces of nanoparticles and the strong selfassembly ability of the molecules is the driving force for the ordered arrangement of nanoparticles. This method opens a new way to build spherical nanoparticles into untraditional nanostructures. Gold nanoparticles, due to their potential of building metamaterials that possess novel optical properties, such as negative refractive index and tunable surface plasmon resonance, is of great interest in this field of research. In this thesis, the self-assembly behaviour of a number of T-shaped liquid crystalline molecules have been investigated by small angle X-ray scattering (SAXS) and grazing incidence small angle X-ray scattering (GISAXS) methods and some complicated liquid crystal phases formed by T-shaped bolaamphiphiles have been solved. These T-shaped liquid crystalline molecules, each of which is composed of a biphenyl core ended by two terminal polar groups and a relatively long lateral chain, were found to form several novel structures which have never been realized in any liquid crystalline systems reported before. Using the same experimental methods, the self-assembled nanostructures of liquid crystalline molecules functionalized gold nanoparticles (GNPs) were also investigated. Different ordered superlattice structures including both 2D and 3D ones have been obtained from these hybrid systems. The results show how the mode of self-assembly of gold nanoparticles can be controlled by changing the parameters of coating molecules. Electron density maps of these structures were reconstructed using the diffraction intensities obtained from experimental results. The corresponding model of each structure was also proposed based on the reconstructed electron density maps as well as the structures and dimensions of molecules. Moreover, some simulation work was conducted, for example diffraction intensity simulation, diffraction pattern simulation and molecular dynamic III simulation, and good agreements between experimental and simulation results have been achieved. Finally, with the help of GISAXS technique the morphologies of double layers of gold nanoparticles prepared via layer-by-layer fabrication method have been investigated. By carefully adjusting the distance between adjacent gold nanoparticle layers, a successful control of the coupling of the localized surface plasmon polariton resonance was reported recently. In this thesis the sideway correlation of gold nanoparticles and the correlation between two gold nanoparticle layers were studied. The features observed in GISAXS patterns can be interpreted very well with relatively simple models.
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Mercer, Carolyn Regan. "Liquid crystal point diffraction interferometer." Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187127.
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A new instrument, the liquid crystal point diffraction interferometer (LCPDI), has been developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point diffiaction interferometer (PDI) and adds to it phase stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wavefronts with very high data density and with automated data reduction. This dissertation describes the theory of both the PDI and liquid crystal phase control. The design considerations for the LCPDI are presented, including manufacturing considerations. The operation and performance of the LCPDI are discussed, including sections regarding alignment, calibration, and amplitude modulation effects. The LCPDI is then demonstrated using two phase objects: a defocus difference wavefront, and a temperature distribution across a heated chamber filled with silicone oil. The measured results are compared to theoretical or independently measured results and show excellent agreement. A computer simulation of the LCPDI was performed to verify the source of observed periodic phase measurement error. The error stems from intensity variations caused by dye molecules rotating within the liquid crystal layer. Methods are discussed for reducing this error. Algorithms are presented which reduce this error; they are also useful for any phase-stepping interferometer that has unwanted intensity fluctuations, such as those caused by unregulated lasers. It is expected that this instrument will have application in the fluid sciences as a diagnostic tool, particularly in space based applications where autonomy, robustness, and compactness are desirable qualities. It should also be useful for the testing of optical elements, provided a master is available for comparison.
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Haddock, Joshua Naaman. "Liquid Crystal Based Electro-Optic Diffractive Spectacle Lenses and Low Operating Voltage Nematic Liquid Crystals." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1304%5F1%5Fm.pdf&type=application/pdf.
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Gopalanarayanan, Bhaskar. "Analysis of Thermoplastic Polyimide + Polymer Liquid Crystal Blends." Thesis, University of North Texas, 1998. https://digital.library.unt.edu/ark:/67531/metadc279285/.
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Thermoplastic polyimides (TPIs) exhibit high glass transition temperatures (Tgs), which make them useful in high performance applications. Amorphous and semicrystalline TPIs show sub-Tg relaxations, which can aid in improving strength characteristics through energy absorption. The a relaxation of both types of TPIs indicates a cooperative nature. The semicrystalline TPI shows thermo-irreversible cold crystallization phenomenon. The polymer liquid crystal (PLC) used in the blends is thermotropic and with longitudinal molecular structure. The small heat capacity change (ACP) associated with the glass transition indicates the PLC to be rigid rod in nature. The PLC shows a small endotherm associated with the melting. The addition of PLC to the semicrystalline TPI does not significantly affect the Tg or the melting point (Tm). The cold crystallization temperature (Tc) increases with the addition of the PLC, indicating channeling phenomenon. The addition of PLC also causes a negative deviation of the ACP, which is another evidence for channeling. The TPI, PLC and their blends show high thermal stability. The semicrystalline TPI absorbs moisture; this effect decreases with the addition of the PLC. The absorbed moisture does not show any effect on the degradation. The addition of PLC beyond 30 wt.% does not result in an improvement of properties. The amorphous TPI + PLC blends also show the negative deviation of ACP from linearity with composition. The addition of PLC causes a decrease in the thermal conductivity in the transverse direction to the PLC orientation. The thermomechanical analysis indicates isotropic expansivity for the amorphous TPI and a small anisotropy for the semicrystalline TPI. The PLC shows large anisotropy in expansivity. Even 5 wt. % concentration of PLC in the blend induces considerable anisotropy in the expansivity. Thus, blends show controllable expansivity through PLC concentration. Amorphous TPI + PLC blends also show excellent film formability. The amorphous TPI blends show good potential for applications requiring high thermal stability, controlled expansivity and good film formability.
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Debnath, Asim. "Formulation and characterization of room temperature ferroelectric and antiferroelectric liquid crystal mixtures." Thesis, University of North Bengal, 2018. http://hdl.handle.net/123456789/2783.
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Huang, Danding. "Ferroelectric liquid crystal display based on photo-aligned azo-dye layers /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202004%20HUANGD.
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Wang, Xinghua. "Liquid Crystal Diffractive Optical Elements: Applications and Limitations." [Kent, Ohio] : Kent State University, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1122499777.
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Thesis (Ph.D.)--Kent State University, 2005.Title from PDF t.p. (viewed Sept. 14, 2006). Advisor: Philip J. Bos. Keywords: liquid crystal; diffractive optical element; optical phased array; spatial light modulator; high resolution wavefront control; aberration correction. Includes bibliographical references (p. 206-213).