Dissertations / Theses: 'Discotic liquid crystals'

1

Tearle, William Mark. "Chemically induced discotic liquid crystals." Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296362.

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Vanderstraeten, Petra Emma. "Towards redox-active discotic liquid crystals." Thesis, Heriot-Watt University, 2004. http://hdl.handle.net/10399/317.

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McBride, Lever Leon James. "Charge transport in discotic liquid crystals." Thesis, University of Leeds, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435786.

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Kruglova, Olga Viktorovna. "Discotic liquid crystals : from dynamics to conductivity /." Amsterdam : IOS Press, 2007. http://www.loc.gov/catdir/toc/fy0803/2007464234.html.

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5

Turner, J. E. "Lyotropic discotic dye/water systems." Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384089.

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Tate, Daniel James. "Applications of discotic liquid crystals in organic electronics." Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493791.

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The future development of printable organic field-effect transistors requires the development of high mobility organic semiconductors; particularly n-type and ambipolar semiconductors. This thesis is concerned with the development of discotic liquid crystal semiconductors which are suitable for such applications.

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Laschewsky, André. "Monolayers and Langmuir-Blodgett multilayers of discotic liquid crystals?" Universität Potsdam, 1989. http://opus.kobv.de/ubp/volltexte/2008/1739/.

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Contents: 1. Discotic Liquid Crystals 2. Monolayers and Langmuir-Blodgett Multilayers 3. Theoretical Considerations on the Molecular Packing of Discotic LCs in Monolayers and Multilayers 4. Spreading Experiments with Discotic LCs 5. LB-Multilayers of Discotic LCs 6. Polymeric Discotic LCs 7. Summary

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8

De, Luca Marc Dominic. "Molecular dynamics simulations of calamitic and discotic liquid crystals." Thesis, Sheffield Hallam University, 1997. http://shura.shu.ac.uk/3187/.

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Significant progress has been made in recent years in modelling liquid crystal phases using the Monte Carlo and molecular dynamics simulation techniques. We describe the technique of molecular dynamics in the microcanonical ensemble that we have used in simulations of liquid crystal systems. A review and discussion of some of the important simulations that have been performed to date on non-spherical hard particle models, soft anisotropic single site models, and realistic atom-atom based models is presented. We report the results of molecular dynamics simulation studies of a system of particles interacting via an anisotropic potential proposed by Luckhurst and Romano, scaled by part of the well depth formulation employed by Gay and Berne. The resultant hybrid Gay-Berne Luckhurst-Romano (HGBLR) potential has an approximately spherical hard core with anisotropic long range attractive interactions with a dependency on the intermolecular vector joining a pair of sites. The spherical hard core nature of individual HGBLR centres notwithstanding we have parameterised single-site HGBLR centres to represent both calarnitic and discotic mesogens. Both systems are shown to exhibit a range of mesophases on cooling from the isotropic liquid to form a crystal, including uniaxial-nematic and columnar-like phases. Unlike previous hard particle studies these ordered phases obtain because of the presence of the long range attractive interactions. A comparison between the different structures formed with the two different parameterisations is presented including graphical representations of the simulation cell . In order to more closely represent the short range anisotropic interactions of real mesogens, a 3-HGBLR-site model has been parameterised to represent the mesogen para-terphenyl. Details of the parameterisation are discussed. Two versions of this model, a twisted central site 3-HGBLR-site site model obtained from a molecular mechanics minimum energy conformation of para-terphenyl, and an all coplanar 3-HGBLR-site site model have been studied using the molecular dynamics technique. The resultant models are found to be biaxial unlike previous anisotropic single site studies utilising soft potentials. Both models appear to exhibit a variety of uniaxial and biaxial mesophases but inclusion of the twisted site appears to promote the formation of biaxial phases. A comparison of the two models is made.

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Mason, Lee Andrew. "Conduction and electrochemical properties of novel discotic liquid crystals." Thesis, University of Leeds, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.400170.

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10

Zhong, Tingjun. "The thermodynamic behaviour and miscibility of discotic liquid crystals." Thesis, University of York, 2015. http://etheses.whiterose.ac.uk/11833/.

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This thesis is concerned with the self-organization of molecules that have disc-like shapes. The disc-like molecules may have relatively rigid structures as in polyaromatic systems, or they may have amphiphilic structures with polyaromatics at their cores, and soft outer shells made up of aliphatic chains. This research seeks to explore molecular compatibility and the ensuing structures formed by such disc- like systems through the study of phase diagrams. Thus, the thermodynamic behaviour and miscibilities of discotic liquid crystal materials were investigated by the formation of Gibbs phase diagrams and calculations using the Schröder-van Laar equation for liquid crystals that have structural common features. Polyaromatics were reviewed and investigated as they are hard discs, and are as the central cores of the molecules that form discotic liquid crystals. Existing discotic materials, such as triphenylene hexa-esters, phenyl hexa-esters, phenyl hexa-alkynes, and rod-like compounds such as benzoate esters were studied and analysed using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction where appropriate, for the preparations of mixture studies. Mixture series made by triphenylene derivatives with each other, and with rod-like molecules or star-shape molecules were prepared and examined in order to investigate the potential co-miscibilities for both discotic nematic phase and hexagonal columnar phases. Mixture series made by triphenylene derivatives with polyaromatics were also prepared, and examined by POM and DSC to explore the virtual N-I phase transition temperatures for polyaromatics. These studies appear to show that nematic discotic materials are liquid crystals, whereas columnar materials exhibit 2D crystallinic soft solid phases. In addition, a novel new phase was found to form in the isotropic liquid of mixtures of polyaromatic materials, suggesting the possibility of the cubatic nematic phase being present.

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Tant, Julien. "Discotic liquid crystals as organic semiconductors for photovoltaic device applications." Doctoral thesis, Universite Libre de Bruxelles, 2004. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211134.

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Les sources d'énergie renouvelable connaissent un essor grandissant. Parmi celles-ci se trouvent les cellules photovoltaïques. Elles ont pour objet la transformation de la lumière en électricité. Les dispositifs actuels, basés sur le silicium, nécessitent des matériaux de très grande pureté et de hautes températures de mise en œuvre, les empêchant de concurrencer les principales sources d’énergie actuelles (fossile, nucléaire).

Une alternative pourrait provenir des matériaux semi-conducteurs organiques. En effet, l’utilisation de méthodes de mise en œuvre à partir de solutions pourrait permettre la fabrication de dispositifs flexibles et bon marché. Des résultats encourageants ont été obtenus avec des polymères conjugués et de petites molécules organiques. Les cristaux liquides discotiques CLDs forment une catégorie particulièrement intéressante de matériaux. Ils ont en effet la capacité de s’organiser spontanément en colonnes de molécules, formant des semi-conducteurs à une dimension. Leurs propriétés intéressantes en tant que semi-conducteurs, combinées à une mise en œuvre facile, en font de bons candidats pour de futures applications.

Dans ce travail, deux familles complémentaires de matériaux discotiques ont été développées, formant une paire de semi-conducteurs de type n et p. Leurs structures chimiques ont été étudiées en vue d'obtenir des matériaux possédant un ensemble de propriétés choisies afin d’optimiser les paramètres clefs du processus de photo-génération de charges. Ces propriétés sont les suivantes: forte absorption de la lumière dans le visible, fort caractère semi-conducteur de type n ou p, pas de phase cristalline à température ambiante, présence d'une phase cristal liquide colonne, phase isotrope en dessous de 200°C. De plus, les matériaux doivent être accessibles en un nombre minimum d’étapes d’une synthèse efficace, et ce avec un haut niveau de pureté. Ils doivent également être fortement solubles dans les solvants organiques usuels.

Cette étude comporte, pour chacune des deux familles de matériaux, le design de leur structure chimique, leur synthèse et la caractérisation de leurs propriétés physiques (thermotropes, optoélectroniques, électrochimiques). Comme possible semi-conducteur de type p, cinq dérivés tétrasubstitués de la phthalocyanine non-métallée ont été synthétisés, donnant un matériau possédant l’ensemble des propriétés recherchées. Comme possible semi-conducteur de type n, six dérivés hexasubstitués de l’hexaazatrinaphthylène ont été étudiés. L’un d’eux possède les propriétés requises.

Finalement, les propriétés optoélectroniques et photovoltaïques de mélanges des deux matériaux les plus prometteurs, ensemble ou avec d’autres matériaux, ont été étudiées. Des cellules solaires de rendement maximum de 1 % ont été obtenues pour deux dispositifs de compositions différentes.

Ces rendements, bien qu’inférieurs à ceux obtenus précédemment par d’autres groupes (jusqu’à 34 % à ce jour), sont néanmoins révélateurs des potentialités des matériaux organiques, et plus particulièrement des cristaux liquides discotiques, pour de futures applications dans le domaine des dispositifs électroniques.

Doctorat en sciences, Spécialisation chimie
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Towlson, David Stephen. "Mesophase behaviour in a system of self-assembling discotic amphiphiles." Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238552.

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13

Zeng, Erman. "Design, synthesis and characterization of columnar discotic and bowlic liquid crystals." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/12268.

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14

Stackhouse, Philip Jeffrey. "The design, synthesis and mesomorphic properties of discotic liquid crystals." Thesis, University of Hull, 2008. http://hydra.hull.ac.uk/resources/hull:1360.

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Discotic liquid crystal research is now more than 30 years old, however it is still early days compared with the well-established area of calamitic liquid crystal research which dates back for more than a century. Since the 1990’s there has been great deal of interest in discotic liquid crystal research, due to applications such as discotic compensation films for enhancing liquid crystal display (LCD) viewing angles and exciting new potential applications such as organic semi-conductors and photovoltaics.The work contained in this thesis can be broken down into three major areas: investigation of synthetic methodologies of hexasubstituted triphenylene-based discotic liquid crystals, examination of structure-property relationships within novel triphenylene-based discotic liquid crystalline materials, and the design and mesomorphic properties of novel disc-shaped molecular architectures.The investigation of the synthetic methodologies of triphenylene-based liquid crystals examined two main areas of the synthesis of triphenylene-based discotic materials: iodination reactions to generate valuable intermediates, and the oxidative strategies and methods for the generation of hexasubstituted triphenylenes. These investigations have revealed that careful control over reaction conditions can offer great selectivity in the synthesis of halogenated intermediates for the synthesis of triphenylene-based liquid crystals and that electron rich intermediate species offer the greatest scope for the synthesis of hexasubstituted triphenylenes in good yield and purity.The determination of structure-property relationships within triphenylene-based discotic liquid crystals has examined various peripheral substituents and various near-core modifications to the conventional discotic liquid crystal.A small number of novel spiral-shaped materials have been synthesised, which have revealed interesting mesomorphic properties. These materials have shown the ability to self-organise in such a manner as to fill free space around central disc units so as to generate columnar mesophases in materials which would not otherwise be expected to exhibit mesomorphism.

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15

Kulkarni, Rahul. "Unique Morphology and Structure of New Organic Porphyrin Based Discotic Liquid Crystals." University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1271041395.

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16

Al-Lawati, Zuhoor Hassan Habib. "Surface controlled alignment of discotic liquid crystals on self assembled monolayers." Thesis, University of Leeds, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.581450.

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The alignment of liquid crystal (LC) materials at surfaces is important for many applications such as those in the display industry and chemical and biological sensors. The alignment of thermotropic calamitic LC is an interesting field of research and has been studied well. However, little has been done in the area of discotic liquid crystals in general and in the field of the lyotropic discotic liquid crystal in particular. Discotic liquid crystals have gained interest recently due to their electrical conduction in one dimension, which makes them potentially useful for electronic devices such as transistors, light emitting diodes and solar cells. The alignment of discotic liquid crystals on self-assembled mono layers (SAMs) of alkanethiols has been the focus of this investigation. Both lyotropic (TP6E02M) and thermotropic (HA T11 and RJB66C) discotic liquid crystals were studied on various SAMs. Anchoring at the phase transitions was studied by tracking the shift in the Brewster angle as a function of temperature using Evanescent Wave Ellipsometry (EWE). Modelling to support the EWE experiments has been employed. For the nematic TP6E02M phase, EWE experimental results revealed random planar alignment on both CH3 and COOH functionalised alkanethiol SAMs. The shift in the Brewster angle was in good agreement with the modelling for a random planar alignment over a range of concentrations. In order to understand this behavior, EWE adsorption studies of dilute TP6E02M solutions on both high and low energy surfaces were also preformed. On each SAM a monolayer of the surfactant formed with the hydrophilic side chains of the TP6E02M molecules extending from the interface.

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Forde, Declan J. "FTIR and X-ray investigation of triphenylene based discotic liquid crystals." Thesis, Sheffield Hallam University, 2000. http://shura.shu.ac.uk/19655/.

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Novel disc like molecules based on hexa-n-alkoxy benzoates of triphenylene were synthesised at Hull university. The compounds exhibited thermotropic liquid crystalline behaviour. The compounds differed chemically based upon the number and position of methyl additions to the ester benzoate linkage. Unsymmetrical compounds based on hexa-n-alkoxy triphenylenes were also examined. A number of techniques were employed to observe and measure the physical properties of these compounds. Polarising optical microscopy was used to observe and record the phase behaviour. Typical schlieren nematic textures were often observed in the liquid crystalline phase. The transition temperatures of the phase transitions were recorded to within +/-0.1 °C. Methyl additions to the ester benzoate linkage plays a major role in determining transition temperatures and also the ranges of liquid crystal phase. X-ray diffraction investigations allowed the molecular planar spacings to be measured, use of a heating stage enabled measurements to be taken in the liquid crystalline phase. All the samples produced a diffuse broad diffraction ring in the liquid crystalline phase, indicating that the samples are not highly ordered and that they are likely to have adopted a hexagonal packing arrangement. Planar spacings measured were in the range 22 - 30A, only one sample, DB26, showed a diffraction ring corresponding to a planar spacing of 4.1A, indicating that molecular columns or partial columns were able to form from molecules stacking one on top of another. Thus methyl groups on the ester benzoate linkage disrupt the formation of columns, in turn reducing transition temperatures. A number of methods of successfully aligning the discotic materials using surface treatments are presented. Rubbed PVA and HTAB layers aligned the samples hometropically, while SiO deposited layers aligned the samples homogeneously. (The SiO deposition used an evaporation angle of 45°, a deposition angle of 5° is commonly used to obtain homotropic alignment of calamitic materials.) Methods that produced homogeonous alignment of calamitic materials produced hometropically aligned discotic materials and vice-versa. FTIR allows conformational information about a molecule to be determined. The CH[2] wagging region was investigated to determine conformational information relating to the alkyl arms. Combination of FTIR and aligned samples allowed the alignment process to be investigated, it was determined that the alignment of the molecules occurs in a series of stages, the triphenylene cores align first on cooling, followed by the ester benzoate linkages and finally the alkyl arms. Computer modelling simulations allowed various molecular conformations to be observed, combination with X-ray diffraction data allowed molecular structures to be generated. The software allowed various molecular dimensions to be easily measured and the effect and extent of interdigitation of molecular arms to be observed. The molecular dynamics calculations were only able to calculate energy minimisations for crystalline structures, but the crystalline results offered valuable insights into the liquid crystalline structures and behaviour.

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Hindmarsh, Paul. "Investigation of the structure/property relationships in triphenylene discotic liquid crystals." Thesis, University of Hull, 1996. http://hydra.hull.ac.uk/resources/hull:13390.

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This thesis presents a detailed investigation of the relationship that exists between the molecular structure and the mesomorphic behaviour in discotic liquid crystals. This was achieved by the systematic alteration of the molecular architecture of one class of discotic liquid crystals - the triphenylen-2,3,6,7,10,11-hexayl hexakis(4-alkoxybenzoate)s which were first studied in 1981. It was shown, by the systematic increase in the lateral substituents (from hydrogen through to tert-butyl, both mono- and di-substituted) in both the outer and inner regions of the peripheral phenyl rings of these triphenylene benzoates, that both the position and size of the substituents greatly affect the melting points, transition temperatures and phase morphology. Studies on lateral substitution were also conducted using polar units and these results were equally remarkable. Examination of the effects of lengthening the peripheral arms, without lateral substituents of the triphenylene benzoates was also performed and with the results obtained, it allowed at last, the construction of a complete theoretical model for the relationship that exists between the molecular structure of discotic liquid crystals and the mesophase behaviour.

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Rungsirisakun, Ratana. "Towards semiconductor junctions based on discotic liquid crystals and templated inorganic oxides." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.658559.

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This thesis is concerned with the investigation of organogelating triphenylene derivatives as templates for the sol-gel deposition of metal oxides including Ti02 and WO3. The goal was to make p-n junction devices, hybrid Ti02/triphenylene or WO3/triphenylene. Triphenylene acts as a p~type semiconductor, and the metal oxide acts as an n-type semiconductor. The photoelectrochemical properties of some prototype devices 0 were investigated. This thesis is structured in eight chapters. Chapter one reviews sol-gel chemistry which is the best route to synthesise nanostructured inorganic oxides, the use of organic templates in the sol-gel process, and the experimental techniques commonly used to characterise structured inorganic oxides. Chapter two reviews the electrochemistry of organic semiconductors, including triphenylene compounds, the electrochemistry of Ti02 and WO), and the goals of this project. In Chapter three, the gelating and silica templating properties of a well-known triphenylene, TP6E02M are investigated. TP6E02M forms gels in aqueous solution at high concentration. For the first time, cyclic voltammetry is used to characterise the solution and gel states of this compound. TP6E02M is shown to be a poor template for silica deposition. In Chapter four, the organogelating and silica templating properties of Aida-type triphenylenes (with alkyl-ethyleneoxy side chains) are investigated. These include a novel compound, TP6C 16E03M. It is shown that none of these triphenylene compounds formed gels in any of the solvents investigated. The composite silica films prepared according to Aida's method seem, however to contain fibrils. In Chapter five, the organogelating and silica templating properties of Ansell-type triphenylene (with amino acid side chains) are investigated. It is shown for the first time that organogels are formed by TP6AcAOH in DMSO, TP6AcAOH in EtOH/H20, TP6AcAOH In MeOH/H20, TP6AcAOEt in EtOH, and TP6AcDEA in MeOH. The self-assembly of TP6AcAOH is pH-switchable. All of these gels are characterised using different techniques. The gel fibres probably consist of multiple aggregated stacks of triphenylene. The silica templated with TP6AcAOEt in ethanol using water as catalyst consisted partially of rod-like nanoparticles. In Chapter six, the sol-gel synthesis of templated WO) is investigated. It is shown that Pluronic F127 can act as a template in the sol-gel synthesis of WO), affecting the morphology of the obtained product, when WCI6 is used as the reactant. We obtained aggregates of short, rod-like nanoparticles with 0.1 g F127, and aggregated spherical particles with 0.3 g F 127. In Chapter seven, hybrid triphenylene-WO) and triphenyleneTi02 devices are constructed and their photochemical properties are investigated. Neither type of devices seems to behave as a p-n junction but this may be because the partically reduced, conducting form of WO) is present, while Ti02 may be present in the wrong crystalline form. In Chapter eight, future possibilities for composite triphenylene/metal oxide devices are considered.

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McNeill, Andrew. "Discotic liquid crystals as molecular wire interconnects in 3D stacked computer chips." Thesis, University of Leeds, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410957.

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21

Chau, Sotheary. "An investigation of the effect of benzene substitution pattern on the formation of discotic phases." Thesis, Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/27672.

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22

Haslam, Simon David. "Scattering studies of discotic liquid crystals in the bulk and in thin films." Thesis, University of Bristol, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240592.

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23

Dotson, Darin Lee. "Part 1. the mesomorphic properties of arloxy-s-triazines and their analogs, Part 2. the synthesis and polymerization behavior of α-aminonitriles and related compounds." Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/39575.

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24

Scioneaux, Ashley Nicole. "Design, Synthesis and Characterization of m-Phenylene Ethynylene-Based Macrocycles as Discotic Liquid Crystals." Miami University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=miami1323375345.

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25

Gopee, Hemant. "Synthesis and characterisation of novel discotic liquid crystals based on triphenylene and phthalocyanine cores." Thesis, University of East Anglia, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398494.

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The discovery of discotic liquid crystals in 1977 by Chandrasekhar has led to an ever increasing interest in the preparation of new discotic mesogens. Research on the potential application of such systems has, however, been held back mostly by synthetic and purification difficulties to obtain enough of the required pure materials. The work described in this thesis (Chapter 2) concerns the synthesis of macrodiscotic structures which led to the formation novel discotic liquid crystalline systems. Nonplanar substituted phthalocyanines have been described by Simon and were found to be mesogenic. We expected that planarising these systems (formation of triphenylene) would have the effect of changing both the absorption (shift to longer wavelength due to extra conjugation) and the mesogenic properties (due to formation of large discs). The syntheses of triphenylenophthalocyanines were achieved using palladium catalysed aryl-aryl cross-coupling as key step in the syntheses. The end materials were characterised and tend to be mesogenic. After the successful synthesis of the triphenylenophthalocyanines, we were in a position to further extend the n-system of our phthalocyanines and the molecules targeted were perylenophthalocyanines (Chapter 3). The syntheses were achieved through a cyc1oaddition reaction as key step. In this case, however, none of the perylenophthalocyanines were liquid crystalline. 3: 1 phthalocyanines were also prepared and tend to be non-mesogenic. A senes of mixed hexyloxy-Ihexylthio-triphenylenes has also been synthesised to determine the structural features governing the formation of helical mesophases shown by HHTI (Chapter 4). It has been shown that four sulphide substituents (plus two alkoxides) are required to induce the additional, more ordered phase. Furthermore, the position of substitution is crucial for its formation. Also, the synthesis and characterization of a series of triphenylenes has been described in which 2, 4 or 6 of the alkyloxy chains of parent hexa(hexyloxy)triphenylene are replaced by heptyl chains (giving mixed alkyl-alkyloxy triphenylenes). This series provides a direct comparison to the derivatives which gives to the rare helical phase. Finally, the synthesis of a few novel triphenylene molecules expected to be on the boundaries between the traditional rod-shaped and disc-shaped structure were achieved. Some of these compounds formed discotic mesophases.

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De, Vos Thierri. "Etude théorique et par simulations d'une phase nématique confinée et torsadée de molécules discotiques." Doctoral thesis, Universite Libre de Bruxelles, 2008. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210483.

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Il est actuellement bien connu que les molécules non sphériques peuvent former des mésophases (ou cristaux liquides), c'est-à-dire des phases dont les propriétés sont intermédiaires entre celles des liquides et celles des cristaux. La mésophase la plus connue est la phase nématique. Il s'agit d'une phase caractérisée par une distribution aléatoire des centres de masse des molécules, mais dans laquelle l'orientation des molécules présente une direction préférentielle, désignée par un vecteur unité appelé le directeur du nématique. Une telle phase possède donc la fluidité d'un liquide tout en présentant, tel un cristal, une biréfringence. C'est cette dernière propriété qui est exploitée dans les applications technologiques, principalement dans les dispositifs d'affichage.

Dans un tel dispositif, le liquide nématique est contenu dans une cellule (il y a une cellule par pixel), et son directeur est manipulé à l'aide d'un champ extérieur, électrique ou magnétique. Pour une bonne compréhension du fonctionnement de ce dispositif, il est essentiel de connaître le profil du directeur à travers la cellule en l'absence de champ extérieur. Dans le cadre de ce travail, nous avons étudié un nématique torsadé, c'est-à-dire dont le directeur décrit une hélice à travers la cellule.

Ce profil est déterminé principalement par les propriétés d'ancrage du liquide nématique sur les parois solides de la cellule. En effet, celles-ci peuvent posséder une direction d'ancrage privilégiée, qui favorise l'alignement du directeur dans une direction particulière. Nous avons considéré ici le cas de directions d'ancrage planaires, c'est-à-dire que le directeur est dans le plan des parois. Alors que l'ajout de parois identiques dans le système induit toujours une non-uniformité spatiale dans la densité du nématique (en comparaison avec un nématique en coeur de phase), l'utilisation de directions d'ancrage différentes induit une non-uniformité orientationnelle dans le directeur du nématique; dans notre cas une torsion. C'est principalement ce profil de directeur torsadé qui nous intéresse ici.

L'objectif général de ce travail consiste donc à étudier les propriétés d'ancrage d'une phase nématique confinée et torsadée, d'une part par une théorie microscopique (théorie de la fonctionnelle de la densité), et d'autre part sur le plan de simulations de Monte Carlo, en particulier dans le cas où les molécules ont la forme de disques (discotiques).

Doctorat en Sciences
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Tomović, Željko. "New discotic liquid crystals based on large polycyclic aromatic hydrocarbons as materials for molecular electronics." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=975919792.

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28

Shen, Xiaodong. "Study of molecular order and dynamics in calamitic and discotic liquid crystals by ²H NMR." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0028/NQ32889.pdf.

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29

Zhang, Liang. "Synthesis and characterisation of novel nematic discotic liquid crystals based on twinned triphenylene and coronene." Thesis, University of East Anglia, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539364.

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To date, the study and application of liquid crystals (LCs) have been spread over the world. Compared to the study of calamitic nematic and discotic columnar LCs, the reports on nematic discotic (No) LCs are limited. In this thesis, we designed and synthesised a series of novel, disc-shaped twinned structures that display No mesophases. In chapter 2 we report the synthesis and mesophase behaviour of a series of triphenylene fused annulenes. Initial studies focused on the synthesis of triphenylene twins, linked through their 2,3-positions via diacetylene spacers. The resulting twin is formally antiaromatic and was found to be too unstable to isolate. Attention was then focused on the intriguing isomeric twins linked via the triphenylene 3,6-positions. Synthesis of the precursor triphenylene diacetylenes was achieved by Sonogashira coupling. Direct coupling was achieved by the catalysis of Cu(I)/Cu(II) in dry pyridine and these optimized conditions also led to isolation of higher oligomers. Stepwise syntheses gave model, open dimeric structures. Analysis of the initial twin, in which the other triphenylene beta-positions held hexyloxy-substituents, revealed the formation of a nematic discotic mesophase. XRD showed the twin adopts a nearly flat conformation and a zig-zag packing style in their crystalline state. Higher oligomers were not meso genic. In chapter 3 we extended our research on twins linked through the triphenylene 3,6-positions, now inserting aromatic groups. A 1,3-diethynylbenzene bridged twin was designed first as it was expected to lead to an unstrained twin. The closed system, which is not conjugated because of the 1,3-phenyl linkers, was achieved by the catalysis of Cu(I)/PPh3/K2C03 in dry DMF, which was applied for the subsequent coupling reactions. Nematic discotic mesophase behaviour was again observed. Formation of the conjugated, strained twin linked through 1,4-diethynylbenzene spacers was attempted but the closure of the system was not successful. Considering the importance of thiophene and its polymers, as well as the stability and angle issue, we employed 2,5-diethynylthiophene as a spacer and the resulting twin was successfully synthesized and gave a stable No mesophase. Bithiophene and 2,2' -bithienylacetylene were also introduced to the twin, and a formally aromatic, unsymmetrical twin was designed and prepared. However, the melting. temperatures of these compounds were above 300°C. Chain extension was investigated to lower the transition temperatures and finally an No mesophase was observed for some derivatives. Chapter 4 describes attempts to prepare related twins based on hexabenzocoronenes (HBCs). The precursor 2,5-diacetylene substituted HBC was synthesized via Sonogashira coupling followed by normal deprotection. The coupling of the diacetylene precursor, however, proved impossible without competing decomposition of the product.

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Leng, Siwei. "From Crystal to Columnar Discotic Liquid Crystal Phases: Phase Structural Characterization of Series of Novel Phenazines Potentially Useful in Organic Electronics." Akron, OH : University of Akron, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1247614330.

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Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Science, 2009.
"August, 2009." Title from electronic dissertation title page (viewed 9/23/2009) Advisor, Stephen Z. D. Cheng; Committee members, Alexei P. Sokolov, Gustavo A. Carri, Darrell H. Reneker, Weiping Zheng; Department Chair, Ali Dhinojwala; Dean of the College, Stephen Z. D. Cheng; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

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Naresh, Shakya Man. "Studies of Electronic Transport in Novel Smectic and Discotic Liquid Crystalline Organic Semiconductors." Kent State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=kent1289418142.

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32

Yoo, Seunghyup. "Organic solar cells based on liquid crystalline and polycrystalline thin films." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1246%5F1%5Fm.pdf&type=application/pdf.

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33

Paul, Sanjoy. "CHARGE TRANSPORT IN LIQUID CRYSTALLINE SMECTIC AND DISCOTIC ORGANIC SEMICONDUCTORS: NEW RESULTS AND EXPERIMENTAL METHODOLOGIES." Kent State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=kent1469836810.

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34

Semyonov, Alexander N. "Design, Synthesis and Characterization of Fluorescent Dyes and Liquid Crystal Semiconductors." Kent State University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=kent1153556141.

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35

Krause, Christina [Verfasser], Andreas [Akademischer Betreuer] Schönhals, Andreas [Gutachter] Schönhals, Regine von [Gutachter] Klitzing, and Mario [Gutachter] Beiner. "Structure and dynamics of discotic liquid crystals in the bulk and in the confined state / Christina Krause ; Gutachter: Andreas Schönhals, Regine von Klitzing, Mario Beiner ; Betreuer: Andreas Schönhals." Berlin : Technische Universität Berlin, 2016. http://d-nb.info/1156017475/34.

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SANTOS, Arthur Bernardo de Souza. "Cromóforos rígidos derivados de tiazol o [5, 4-d] tiazol: cristais líquidos e sais orgânicos fotocromáticos." Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/17508.

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Submitted by Irene Nascimento (irene.kessia@ufpe.br) on 2016-07-21T16:17:26Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) ATUALIZADA DISSERTAÇÃO_ARTHUR_UFPE_.pdf: 6640779 bytes, checksum: 54162674f1fcaee2b4fef8836f21cd72 (MD5)
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CNPQ
O estudo das propriedades de materiais orgânicos tem chamado atenção devido sua versatilidade estrutural e de composição que podem moldar suas propriedades físicas e químicas. Neste trabalho preparamos seis cromóforos rígidos contendo o heterociclo tiazolo[5,4-d]tiazol (Thz) como espaçador aromático, e grupos terminais piridínicos ou carboxílicos. Desta forma trabalhamos com duas linhas de pesquisa: foto-eletroquímica para os derivados piridínicos e síntese e caracterização de cristais líquidos (CLs). Investigamos as propriedades fotoquímicas e processos redox das bipiridinas X,X'-(tiazolo[5,4-d]tiazol-2,5- dil)bis(piridil) (X,X’ = 2,2’; 3,3’ ou 4,4’). Em solução, apresentaram propriedades acidocrômica via foto- e eletrodissociação de solventes clorados. A seguir, preparamos sais de trifluoracetato dos bipiridínio (viologens), que apresentaram propriedades fotocromáticas via transferência de elétron quando expostos à radiação UVB. Utilizamos os derivados carboxílicos como centros rígidos para a preparação de cristais líquidos. Escolhemos o grupo carboxilato como precursor sintético dos conectores orgânicos: éster, amida e 1,3,4-oxadiazol. Planejamos os cristais líquidos contendo tais conectores e cadeias alquílicas dodeciloxi (-OC12H25), obtendo materiais com estrutura geral: centro rígido + conectores + cadeias alcóxi. De acordo com a estrutura dos centros rígidos, preparamos treze mesógenos calamíticos (ácido tiazolo[5,4- d]tiazol-2,5-dicarboxílico), das quais seis apresentaram mesofases calamítica (comportamento esperados) e três apresentaram mesofases discóticas. O fotocromismo apresentado pelos sais de bipiridinas frente à radiação UVB nos permite sugerir aplicações como dosimetria desta radiação, presente na luz solar. As propriedades mesomórficas ainda estão em estudo. No entanto, conseguimos obter CL’s discóticos a temperatura ambiente e uma mesofase discótica nemática, bastante rara.
The study properties of organic materials has drawn attention due to its structural versatility and composition versatility, which can shape their physical and chemical properties. In this work, we prepared six rigid chromophores containing the heterocycle thiazolo[5,4-d] thiazole (Thz) as aromatic spacers, and pyridyl or carboxylic terminal groups. Hence, we have worked with two research lines: photo-electrochemistry for the pyridine derivatives and synthesis and characterization of liquid crystals (LCs). We investigated the photochemical properties and redox processes of the bipyridines X,X'-(thiazolo[5,4-d] thiazole-2,5-diyl)bis(pyridyl) (X,X' = 2,2 '; 3,3' or 4,4 '). In solution, these compounds showed acidochromic properties via photonand electrodissociantion of chlorinated solvents. Next, we prepare bipyridinium trifluoroacetate salts (viologens), which exhibited photochromic properties through electron transfer when exposed to UVB radiation. We used the carboxylic derivatives as rigid centers for the preparation of liquid crystals. We chose the carboxylate group as a synthetic precursor of organic connectors: esther, amide, and 1,3,5-oxadiazole. We plannned the liquid crystal containing these connectors and the alkoxy chains dodecyloxy (-OC12H25), obtaining materials with general structure: rigid center + connectors + alkoxy chains. According to the rigid center structure, we obtained thirteen calamitic (acid thiazolo [5,4-d] thiazole-2,5-dicarboxylic acid), six of which had mesophases calamítica (expected behavior) and three had discóticas mesophases. The photochromic presented by bipyridinium salts when exposed of UVB radiation allows suggest applications such as dosimetry of sunlight radiation. The mesomorphic properties are still under study. However, we obtained room temperatures discóticos LCs, as well as a nematic discótica mesophase which are quite rare.

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37

Holt, Lucy Anne. "Characterisation of nanoparticle-discotic liquid crystal composites." Thesis, University of Leeds, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493770.

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The work carried out in this thesis concerns the understanding of the physical properties of mixtures of nanoparticles and hquid crystals. The nanoparticles that have been used are buckminsterfullerene, carbon nanotubes and surface functionalised gold nanoparticles. The main group of liquid crystals used were discotic liquid crystals, in particular the triphenylene derivative HAT6.

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38

Rigby, Adam. "The computer simulation of discotic and rod-like phase transitions for a range of molecular shapes and sizes." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/the-computer-simulation-ofdiscotic-and-rodlike-phasetransitions-for-a-range-ofmolecular-shapes-and-sizes(9c5b9645-e4c2-440a-b0ec-3533636dd1e9).html.

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In 1970, Freiser made the theoretical prediction that a biaxial nematic phase could exist. In auniaxial nematic, only one particle axis is aligned but with a biaxial nematic, all three molecular axes are aligned. This phase is expected to occur for particle whose shape is intermediate between that of a disc and a rod. Board and bent-core particles are examples of such structures. Despite extensive experimental investigation, however, very few biaxial nematic systems have been found. Yu and Saupe [21] have shown the occurrence of a biaxial nematic phase generated for a lyotropic system. Similarly van der Pol observed a biaxial nematic phase in a colloidal suspension of board-like goethite particles [22]. For thermotropic, molecular systems, however, the situation is less clear-cut. Merkel et al., [23] and Figueirinhas et al., [24] claim that Tetrapodes have can exhibit a biaxial nematic phase, whilst Acharya et al., [25] and Prasad et al., [26] have also suggested the occurrence of this same phase with bent-core molecules, though experimental uncertainty still exist. With regards to theoretical predictions of the biaxial nematic transition, one notes in particular the work of Taylor and Herzfeld [13] on hard sphero-platelets, which predicts a rich phase diagram, notably containing an unusual discotic smectic phase. To date there are few simulations of board-like models, such as Vanakaras et al., [27] being arecent exception, developing a phase diagram for hard board-like colloids. Similarly, Escobedo[28] has produced a phase diagram of hard cuboids. We present molecular dynamics simulation results on a short range repulsive fused-hexagonmodel, somewhat resembling hard boards. Depending on the geometry of the board, we observe uniaxial and biaxial nematics, smectics A and C, a biaxial smectic phase and a columnar phase. Possibly the most interesting result is the existence of the theoretically predicted discoticsmectic. We further investigated the effect of applying both external fields and shears to several of the structures. The former, among other things, aided the alignment of the particles in the phase, removing dislocations. The shear was also seen to increase biaxial ordering, however, it also demonstrates an ability to introduce clear layer fractures, seen when shearing forces became overly dominant. An applied electrical field was able to induce isotropic!biaxial nematic and biaxial smectic switching. Finally we consider briefly less-symmetric arrangements of fused hexagons, including chiral particles. These systems proved hard to equilibrate but discotic nematic phases were observed for certain structures. Chiral clusters were also observed, however, no globally chiral phase was found. Columnar structures were also seen, but showing a weak overall alignment as columnstended to point along several directions.

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Pinto, Jason Christopher. "Field-effect transistors from discotic liquid crystal semiconductors and polymer brush dielectrics." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612816.

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Zhou, Xiaoli. "Synthesis and Characterization of Novel Discotic Liquid Crystal Porphyrins for Organic Photovoltaics." Kent State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=kent1231463813.

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41

Albrecht, O., W. Cumming, W. Kreuder, André Laschewsky, and Helmut Ringsdorf. "Monolayers of rod-shaped and disc-shaped liquid crystalline compounds at the air-water interface." Universität Potsdam, 1986. http://opus.kobv.de/ubp/volltexte/2008/1712/.

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Calamitic (rod-shaped) and discotic (disc-shaped) thermotropic liquid crystalline (LC) compounds were spread at the air-water interface, and their ability to form monolayers was studied. The calamitic LCs investigated were found to form monolayers which behave analogously to conventional amphiphiles such as fatty acids. The spreading of the discotic LCs produced monolayers as well, but with a behaviour different from classical amphiphiles. The areas occupied per molecule are too small to allow the contact of all hydrophilic groups with the water surface and the packing of all hydrophobic chains. Various molecular arrangements of the discotics at the water surface to fit the spreading data are discussed.

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42

Favre-Nicolin, Christine. "Synthèse et photopolymérisation de cristaux liquides discotiques dérivés du triphénylène." Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10053.

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Les cristaux liquides discotiques ont 20 ans. La perspective d'applications exploitant le comportement photoconducteur et les caracteristiques optiques de composes de cette famille a fortement stimule leur developpement. Ces applications requierent en general une grande stabilite mecanique et thermique des proprietes anisotropes mises en jeu. Cette these decrit l'utilisation de la photopolymerisation in-situ de molecules discotiques fonctionnalisees par des groupements acrylate pour stabiliser l'ordre present dans leurs phases liquides cristallines. Cette technique de polymerisation, deja employee avec succes pour les cristaux liquides calamitiques, consiste a d'abord aligner uniformement les monomeres liquides cristallins dans la phase choisie et a ensuite amorcer la polymerisation par voie photochimique. Pour realiser cette etude, nous avons synthetise des derives de benzoates de triphenylene avec 1 a 6 groupements acrylate par molecule. La photopolymerisation de ces monomeres orientes dans la phase nematique discotique n#d conduit, selon qu'ils ont un ou plusieurs groupements acrylate, a des polymeres lineaires a chaines laterales ou a des reseaux polymerises fortement reticules. Ces derniers ont une birefringence negative stable depuis la temperature ambiante jusqu'a plus de 200c, et dont la valeur peut etre ajustee grace a la temperature de polymerisation. Ce manuscrit detaille la synthese, les proprietes liquides cristallines, et la cinetique de polymerisation des monomeres, ainsi que les caracteristiques optiques et structurales de certains des polymeres obtenus. Nous discutons l'influence de la nature chimique des differents monomeres synthetises sur les proprietes finales des materiaux apres polymerisation, et en particulier l'effet du nombre de groupements polymerisables par molecule et celui de la longueur des espaceurs. La photopolymerisation dans les phases cholesterique n#d#* et colonnaire d#h#d, ainsi que la synthese et l'etude de derives du benzene et du phenanthrene, sont egalement abordees.

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Charlet, Emilie. "Mouillage et orientation d’un film mince de cristal liquide colonnaire : de la détermination des propriétés optiques aux applications photovoltaïques." Thesis, Bordeaux 1, 2008. http://www.theses.fr/2008BOR13653/document.

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Cette thèse est consacrée à l’étude de films minces ouverts de cristaux liquides colonnaires sur un substrat solide. Ces matériaux, capables de s’auto-organiser en de larges domaines orientés, sont généralement obtenus à partir de molécules discotiques dérivées de colorants aromatiques. Ces différentes caractéristiques, associées à une bonne mobilité de charges, permettent d'envisager l'utilisation des cristaux liquides colonnaires en film mince dans des dispositifs photovoltaïques. Afin de bénéficier de leurs bonnes propriétés optoélectroniques, les cristaux liquides colonnaires doivent être déposés en film mouillant, d’épaisseur inférieure à 100 nm, et leur orientation contrôlée. Ainsi, pour des applications photovoltaïques, un alignement homéotrope (colonnes normales au substrat) est requis. Inversement, l’orientation planaire uniaxe (colonnes parallèles au substrat), est quant à elle requise pour une utilisation de ces composés dans les polariseurs ou dans les transistors organiques à effet de champ. Dans ce travail, différentes méthodes permettant de contrôler l’alignement de films minces ouverts de cristaux liquides colonnaires ont été développées, permettant d’obtenir aussi bien un ancrage homéotrope par traitement thermique spécifique, qu’un ancrage planaire uniaxe par dépôt préalable d’une couche de téflon. Le contrôle de l’orientation a ainsi permis d’une part de produire un film mince (e ? 50 nm) mouillant en ancrage homéotrope ouvrant la voie vers des cellules solaires organiques efficaces, et d’autre part de déterminer l’ensemble des propriétés optiques (indices complexes anisotropes) de ces matériaux cristallins liquides colonnaires. La dynamique du démouillage et l’état d’équilibre d’un film mince ouvert de cristal liquide colonnaire ont également été étudiés. Les résultats expérimentaux révèlent la formation de gouttelettes anisotropes et la présence d’un film nanométrique lors du démouillage de ce film mince
This thesis deals with columnar liquid crystal studied in the geometry of open supported thin films. Columnar liquid crystals are usually made of disk-shaped molecules derived from aromatic dyes. They are efficient charge transporters with the added capacity to self-assemble in large oriented domains. Consequently, such materials may be used in photovoltaic devices. In order to benefit from their good uniaxial charge mobility, their organization has to be controlled in uniform oriented thin films in the range of thicknesses of typically 100 nm. Homeotropic alignment (columns normal to the interface) is required for solar cells whereas uniaxial planar anchoring (columns parallel to the interface) is needed for applications such as polarizers or organic field effect transistor. Different methods to monitor the alignment in open thin films have been developed in this work, which make possible to achieve either homeotropic anchoring by a specific thermal treatment, or uniaxial planar orientation using a Teflon layer. Based on these orientation skills, a uniform ultra-thin film, free of dewetting and homeotropically oriented, is achieved (down to 50 nm thick) opening the way towards efficient solar cells, and a complete study of the optical properties has been performed (with the determination of the anisotropic complex indices) for different columnar liquid crystals. The dynamics of dewetting and the equilibrium state of a thin supported film have also been investigated. Experimental results show the formation of anisotropic droplets and reveal a nanometric film during dewetting

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44

Thiebaut, Olivier. "Bicouches orientées de cristaux liquides colonnaires pour applications photovoltaïques." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2011. http://tel.archives-ouvertes.fr/tel-00591978.

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Grâce à leurs remarquables qualités de transport de charges et d'autoorganisation, les cristaux liquides colonnaires formés de molécules discotiques dérivées de colorants aromatiques sont des candidats prometteurs pour la réalisation de dispositifs photovoltaïques. Pour profiter à bien de ces propriétés, il est indispensable de maîtriser leur organisation en films minces. Un ancrage homéotrope avec les colonnes perpendiculaires au substrat est ainsi nécessaire pour conduire efficacement les charges aux électrodes. Cet alignement a été obtenu par transition d'ancrage entre un substrat solide et une cathode d'argent permettant d'obtenir des films ultra-minces (environ 25 nm d'épaisseur) homogènes orientés. Par ailleurs, une bicouche de composés discotiques intégralement alignée en ancrage homéotrope a été élaborée. A notre connaissance, ce travail constitue la première preuve de faisabilité d'une hétérojonction donneur - accepteur orientée constituée de cristaux liquides colonnaires.

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45

Ndao, Makha. "Propriétés physiques des cristaux liquides discotiques nanoconfinés." Phd thesis, Université Rennes 1, 2013. http://tel.archives-ouvertes.fr/tel-00979588.

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L'objectif de cette thèse est de mener une étude fondamentale et expérimentale des propriétés physiques des cristaux liquides discotiques colonnaires (CLDCs) confinés dans des matrices poreuses templates hautement ordonnées à l'échelle nanométrique. Les molécules des CLDCs de forme plane, composées de noyaux polyaromatiques rigides entourées de chaînes aliphatiques flexibles fonctionnalisables, sont susceptibles de s'auto-assembler dans des colonnes favorisant ainsi le recouvrement de leurs orbitales électroniques π. Ce qui fait de ces matériaux de véritables candidats pour des applications dans l'électronique moléculaire et la photovoltaïque grâce à la possibilité de migration des porteurs de charges le long de leurs colonnes. Cependant, ces applications nécessitent une bonne maîtrise des paramètres influant sur les mécanismes d'alignement dans les phases colonnaires, sur de grands monodomaines, et de préférence à température ambiante. Une méthode très prometteuse visant à optimiser les longueurs de diffusion des porteurs de charge a été récemment proposée, basée sur la formation de nanofils orientés de CLDCs par auto-assemblage dans des matrices dites " templates " (de moulage). Toutefois, les propriétés structurales, dynamiques et les effets de confinement sur ces technologies restent aujourd'hui mal connus et morcelés et pourraient constituer un véritable verrou scientifique pour leur réalisation. Notre étude s'est portée sur les CLDCs commerciaux (HPT) et le Py4CEH (moins connus) qui sont confinés dans des alumines poreuses (AAO) et du silicium poreux (Sip) de diamètres de pores de quelques dizaines de nm. Les diagrammes de phase ont été d'abord étudiés par DSC puis les effets structuraux ont été approfondis grâce à la diffusion de neutrons. Dans les géométries confinées, nous observons une dépression des températures de transition, un élargissement du domaine de stabilité de la phase colonnaire et l'ouverture d'une hystérèse amplifiée dans les pores de plus petite taille. Un ordre orientationnel très élevé a été trouvé dans les phases colonnaires bulk par la RMN du solide et la structure des systèmes confinés colonnaires, dominée par une distribution radiale avec un ancrage homéotrope a été déterminée. La dynamique moléculaire a été étudiée par diffusion quasiélastique de neutrons. Elle est affectée par le confinement : la dynamique de grande amplitude est fortement ralentie, tandis que la dynamique rapide locale devient régie par une distribution très large de temps caractéristiques.

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Mejia, Mejia Andres Fernando Fernando. "Discotic Colloids." Thesis, 2013. http://hdl.handle.net/1969.1/151142.

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Many materials and biological systems in nature are suspensions composed of disks, such as clay, asphaltenes, and red blood cells. Despite their natural abundance and wide industrial application, disks are least studied compared to spheres and rods, due to the lack of model systems. In our research, disks at micro-scale were mass-produced with unprecedented uniformity in size and shape, and unique flexibility in the control of lateral size, lateral size polydispersity, shape, and aspect ratio (ξ = diameter/thickness). This dissertation focuses on two main areas: the study of the discotic colloidal liquid crystal phase transitions and the application of disk-like colloidal systems as Pickering emulsion and Pickering foam stabilizers. First, we engineered two discotic colloidal systems made from organic and inorganic materials. The former is made of α-eicosene, which is an alkene of 20 carbons. The latter is composed of nano-sheets from exfoliated zirconium phosphate (α-ZrP). Both discotic systems were used to experimentally investigate the liquid crystalline phase transitions (Isotropic-Nematic, Isotropic-Cubic and Isotropic-Columnar). Also, the nematic crystalline phase was studied in detail by embedding it in a translucent and thermo-sensitive hydrogel. This was possible since nematic textures could be formed instantly by ZrP nano-sheets due to their high diameter-thickness ratio. Second, we developed Pickering emulsions and Pickering foams stabilized by high-aspect-ratio nano-sheets. We have also demonstrated for the first time the fabrication of the thinnest amphiphilic Janus and Gemini nano-sheets, which are either surface- or edge-modified plates with a thickness at atomic scale. These nano-sheets were obtained by exfoliating α-ZrP crystals grafted with a coupling agent of hydrophobic molecules on their edges and outer surfaces. Extending this work, we studied crucial fundamental mechanisms that allow Pickering interfacial stabilization, including the effect on the adsorption properties of particle aspect ratio, concentration, and hydrophobicity. Our study is of great interest in the scientific community due to the difficulty in generating a discotic colloidal system of controllable parameters.

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Chang, Ya-Wen. "Discotic Liquid Crystals and Polymersomes: Molecule Goniometers." Thesis, 2012. http://hdl.handle.net/1969.1/ETD-TAMU-2012-08-11635.

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Controlling the assembly of amphiphilic molecules and micron-sized, disk-shaped particles at different length scales into ordered structures enables bottom-up organization which is of great interest to emerging technologies based on structured materials. The primary object of this work is the investigation of structure forming components - Zirconium phosphate (ZrP) discotic particles and polymersomes/ amphiphiles on their self-assembly and interactions. The effect of bilayer architecture of polymersomes on surface reactivity was investigated via fluorescent probing method. Established through complementary experiments, correlation between reactivity and molecule diffusivity in polymer-rich environment revealed the mechanism of reduced reactivity when tethered reactive groups are located deeper within the hydrophilic polymer layer. The phase diagram of charged nanoplatelets was constructed as a function of particle concentration, surface cation moiety, and ionic strength. Influence of surface cation on the isotropic-nematic transition was done by measuring the transition boundaries of discotic suspensions prepared by acid-base exfoliation reaction with a series of exfoliating agents. Furthermore, a novel phase transition was found, where platelet-platelet interaction was influenced synergistically by ionic strength and ion exchange. At low pH, directional inter-platelet attractions lead to the formation of low volume fraction colloidal gels. Alternative surface modification approaches, including biomolecule deposition and alkyl chain grafting were explored. Finally, self-assembly of platelets in emulsions and oil-water interface was examined. Surface modification was applied to link surface properties to stable emulsion-forming ability in mixed surfactant-particle system. Emulsion uniformity was achieved by microfluidic flow focusing method. Surface engineering and interaction control was demonstrated throughout this work to be viable approaches to the fundamental understanding of collective behaviors of individual building blocks.

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Chiang, Cheng-Yan, and 江征晏. "The Self-Assembly of Discotic Liquid Crystals." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/5bc43k.

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碩士
國立中山大學
光電工程研究所
95
Discotic liquid crystals (DLCs), which consist of disc-like molecules, are known to be able to form nematic and columnar mesophases through self-assembly. Because of the high electric charge mobility in one-dimension, DLCs are found to have uses in making electronic and photonic devices, such as organic light emitting diode, photovoltaic and molecular wires. In order to achieve better performance of these applications, it is essential to obtain the desired alignment of the DLCs. The purpose of this study is to investigate the stacking of disk-like molecules and to control their alignment. The materials used in the present studies are HDBP-8 and LC10. In this thesis, we will show that the stack of disk-like molecules is strongly influenced by temperature. We will also discuss how the molecules stacking is influenced by surface free energy. The disk-like molecules tend to stack with face-on when the surface free energy of the substrates is high. On a surface with lower surface free energy, molecules tend to stack with edge-up. In the latter part of the research, substrates are specially treated to have different surface free energies, and molecular stack on these substrates is observed.

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49

Guey, Chen Fuh, and 陳富桂. "Design and Synthesis of Metallomesogens Discotic Liquid Crystals." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/17535208154328045943.

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Abstract:

碩士
國立中央大學
化學學系
83
Four series of disc-like mono- and dicopper complexes were prepared to demonstracte the formation of discotic liquid crystals. The metallic complexes are prepared by reaction of the substituted o-hydroxydibenzoylmethane as ligands with appropriate metal salts. These compounds all exihibit liquid crystalline behavior, upon heating which melts to give birefringent fluid phases with columnar superstructure as is often observed for disc-like molecules. DSC analysis shows a large enthalpy (10.0-30.5 Kcal/mol) for the crystal-to liquid crystal transition at lower temperature (75-95 degree-C) and a relatively low enthanlpy (0.5-2.0 Kcal/mol) for the liquid crystal-to- isotropic transition at higher temperature (220-260 degree-C). Dicopper complexes as expected. Induction of liquid crystallinity of these metallic complexes is controlled by weak intermolecular dative coordination. Thermal stability of these complexes is senstive to the the number and the carbonlength of the side chains. when slowlyeir isotropic phases, these compounds display pseudo focal conic textures with linear bifringent defects, indicating hexagonal columnar structures. the mesophase structure for these complexes is characterized as Dhd by DSC analysis and optical texture. Detailed XRD experiment is in process to conform the structure of mesophase.

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50

Chang, Lun-hao, and 張倫豪. "Preparation and Electro-Optical Property of Discotic Liquid Crystals." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/73479331002497263211.

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碩士
國立中山大學
光電工程學系研究所
100
In this thesis we synthesize discotic liquid crystal materials. After demonstrating the molecular structures by 1H-NMR of Acid-6, we measure the properties of this material. We use discotic liquid crystal Acid-6 and measure its’ properties. It shows the properties of Acid-6 which is having the ability of absorbing visible light. By UV-Vis spectrum, we can realize the absorption band is located at 400 nm and confirm that it is able to be a photo-sensitized dye. Besides, the property of discotic liquid crystal is the self-assembly ability, the molecular can assemble into hexagonal columnar structure by themselves, which enable discotic liquid crystal to have better mobility. The DSSCs have good power conversion efficiency with using discotic liquid crystals Acid-6. We can measure its’ mobility to know the component with which the most appropriate.

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