468 research outputs found

    Handbook Of Liquid Crystal Research

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    Synthesis And Characterization Of Some Calamitic Liquid Crystals Consisting Of Cholesterol, Rod-Like Imine And Biphenyl-4-Carboxylate Components [QD923. H111 2006 f rb].

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    Sebanyak tujuh siri hablur cecair kalamitik berjaya disintesis dan dicirikan. Kesemua hablur cecair tersebut dibahagikan kepada tiga jenis yang berlainan berdasarkan struktur teras masing-masing, sama ada komponen kolesterol, imina aromatik berbentuk rod atau bifenil-4-karbosilat. Seven series of calamitic liquid crystals were successfully synthesized and characterized. These liquid crystals are categorized into three different types according to their core structure; either a cholesterol, rod-like aromatic imine or biphenyl-4-carboxylate component

    Synthesis And Characterization Of Hydrogen Bonded Side Chain Liquid Crystalline Polymers

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    Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2011Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2011Son yıllarda, supramoleküler sıvı kristaller gibi, yeni sıvı kristal malzemelerin hazırlanmasında hidrojen bağı uygulamaları hızla gelişmektedir. Supramoleküler sıvı kristaller, moleküler türlerin, hidrojen bağları gibi kovalent olmayan moleküller arası kuvvetler vasıtasıyla oluşturdukları komplekslerdir. Mesojenik özellikler, çeşitli proton verici ve proton alıcı gruplarla kolayca değiştirilebilir ve başlangıç türlerinin özelliklerinden farklı yeni sıvı kristal özelliklere sahip supramoleküler yapılar elde edilebilirler. Hidrojen bağlı sıvı kristal malzemeler, gösterge, biyomalzeme ve elektro-optik malzemeler için çeşitli uygulama potansiyeline sahiptirler. Bu çalışma, hidrojen bağ alıcı olarak üç farklı polimerin ve hidrojen bağ verici olarak üç farklı 4 -(n-hidroksi alkoksi)-4-siyanobifenil türevlerinin (n=6,8,11) hazırlanarak, H-bağlı yan zincir sıvı kristal polimer sentezinde kullanımlarını tanımlamaktadır. İlk aşamada, hidrojen bağı alıcı polimerler poli(vinil imidazol) ve poli(4-vinil piridin), monomerlerinin serbest radikal polimerizasyonu ile hazırlanmıştır. Poli(vinil pirolidon) ticari olarak elde edilmiştir. Hidrojen bağı verici bileşikler, farklı sayıda metilen grubu içeren hidroksi halojenürler ile hidroksi siyano bifenil mesojenlerinin reaksiyonu ile sentezlenmiştir. İkinci aşamada, hidrojen bağ verici bileşiklerin hidroksil grubu ile hidrojen bağ alıcı polimerlerin imidazol, pirolidon ve pridin grupları arasındaki H-bağı etkileşimleri vasıtasıyla istenilen H-bağlı yan zincir sıvı kristal polimerler hazırlanmıştır. Hidrojen bağı oluşumu FT-IR spektroskopisi yöntemiyle kanıtlanmıştır. Sıvı kristal özellikleri saptamak ve 4 -(n-hidroksi alkoksi)-4-siyanobifenil türevlerinin ve hidrojen bağlı polimerlerinin sıvı kristal fazlarını belirlemek için, Diferansiyel Taramalı Kalorimetre (DSC) ve Polarize Optik Mikroskop (POM) kullanılmıştır. Hidrojen bağı ve dipolar etkileşiminin birleşimi sıvı kristal davranışların oluşumuna neden olmuştur.Recently, the application of hydrogen bonding in the formation of new liquid crystalline materials, ie. supramolecular liquid crystals has been rapidly developed. Supramolecular liquid crystals are molecular complexes generated from complexation of molecular species through non-covalent intermolecular forces, e.g. hydrogen bonding. The mesogenic properties can be easily modified by several proton donors and proton acceptors, and new liquid crystalline properties, which are different from those of their original moieties, can be obtained by supramolecular structures. Hydrogen bonded liquid crystalline materials have various potential in the fields of display, biomaterials and materials for electro-optical applications. This study describes the preparation of three different polymers as hydrogen bond acceptor and three different 4 -(hydroxyalkoxy)-4-cyanobiphenyl derivatives (n=6,8,11) as hydrogen bond donor. In the first step, poly(vinyl imidazole)(PVI) and poly(4-vinyl pyridine) (PVP) hydrogen bond acceptors were prepared by free radical polymerization of related monomers. Poly(vinyl pyrrolidon) was purchased commercially. The hydrogen bond donors were synthesized by the reaction of hydroxy halides having different number of methylene unit with hydroxy cyano biphenyl mesogens. In the second step, the hydrogen bond donors were attached to the proton acceptor polymers through H-bond interactions between the hydroxyl group of hydrogen bond donors and imidazole, pyrrolidone and pyridine groups of the hydrogen bond acceptors to yield the desired side chain liquid crystalline polymers. The formation of H-bond was confirmed by using FTIR spectroscopy. To confirm the liquid crystalline nature and to identify the phases of 4 -(hydroxyalkoxy)-4-cyanobiphenyl derivatives and corresponding H-bonded polymers, differantial scanning calorimetry (DSC) and polarising optical microscopy (POM) were employed. The co-operation of hydrogen-bonding and dipolar interactions resulted in the formation of LC behaviour.Yüksek LisansM.Sc

    Discotic liquid crystalline star-shaped hetero heptamers for organic photovoltaic devices.

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    This thesis describes synthetic approaches to heteroheptamers of discotic liquid crystals, which should be ideal building blocks for organic photovoltaic devices. Hexaazatriphenylene-hexacarboxylic acid [HAT(CO2H) 6] and its derivatives were chosen as n-type semi-conducting central discotic monomer that has six p-type semi-conducting hexaalkoxytriphenylene discogens covalently attached to it. HAT derivatives were successfully synthesized and their conversions with alkyl alcohols and amines to hexaesters and hexa-amides are discussed. A complete conversion of all acid or ester groups with low molecular weight alcohols and amines was not achieved but transesterification of the hexa-methylester with alkyl alcohols catalyzed by titanium (IV) isopropoxide gave 80--90% conversion. Optimization of the reaction conditions should result in a 100% conversion. Monofunctionalized hexaalkoxytriphenylene derivatives were chosen as p-type semi-conducting ligands and several different synthetic pathways towards these triphenylene derivatives are presented. Several approaches based on statistical cyclization to the triphenylene or statistical cleavage of one alkoxy group have been reported in literature. We, however, could not reproduce the reported yields and found the Suzuki cross-coupling pathway to be the most reliable and highest yielding synthetic approach. The preparation of heteroheptamers containing [HAT(CO2H) 6] as central core and hexaalkoxytriphenylene derivatives as ligands should be straightforward based on the synthetic approaches that have been developed in this thesis. (Abstract shortened by UMI.)Dept. of Chemistry and Biochemistry. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2003 .J35. Source: Masters Abstracts International, Volume: 43-01, page: 0211. Adviser: Holger Eichhorn. Thesis (M.Sc.)--University of Windsor (Canada), 2004

    Computer simulation of liquid crystals

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    A review is presented of molecular and mesoscopic computer simulations of liquid crystalline systems. Molecular simulation approaches applied to such systems are described and the key findings for bulk phase behaviour are reported. Following this, recently developed lattice Boltzmann (LB) approaches to the mesoscale modelling of nemato-dynamics are reviewed. The article concludes with a discussion of possible areas for future development in this field.</p

    Synthesis And Characterization Of New Series Of Liquid Crystalline Compounds Containing Azobenzene And Bisazobenzene Moieties

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    New molecular structures based on azobenzene and bisazobenzene mesogenic units, which can support mesophase were prepared, in particular four different types of liquid crystalline materials have been synthesized and characterized, following the general criteria. All materials were characterized by spectroscopic methods (FT-IR, NMR, MS and CHNS analyses) and the liquid crystalline properties were investigated using differential scanning colorimetry (DSC), optical polarizing microscopy (OPM) and, X-ray diffraction. The presence of smectic A mesophase was confirmed by the textures and X-ray diffraction studies (XRD). The calamitic liquid crystals (rod-shaped) compounds were generally synthesized via diazotization of primary aromatic amine, coupling with phenol and subsequent etherification of phenol with ten fold excess of an appropriate α,ω-dibromoalkane which was further etherified in methanol to give the final compounds, giving rise to a typical features of calamitic liquid crystals (rod-shaped) compounds. Four of the liquid crystalline compounds containing azobenzene moiety denoted as AZOn series, exhibited enantiotropic smectic A phase AZO3-AZO6 (C3-C6) while, compound AZO8 (C8) show monotropic smectic A phase. The liquid crystalline trimer (AZOTn series) containing azobenzene with a short acetyl mesogenic group and a biphenyl as central mesogenic core were prepared by employing the procedures described for the calamitic mesogenic compounds above. The final compound was produced by etherification of the 4`4-hydroxybiphenyl with two-fold mole ratio of 1-bromoalky-(4-phenylazo)acetophenone. Compound with C5 polymethylene flexible alkyl spacer (AZOT5) exhibited enantiotropic nematic and smectic A liquid crystalline properties. While the compound with C6 polymethylene flexible alkyl spacer showed an enantiotropic nematic phase, the (AZOT6) exhibited the higher values of melting and clearing temperatures. The calamitic bisazobenzene liquid crystal series (BAn series) were synthesized from 4-phenylazoaniline as mentioned above. All the compounds were found to show enantiotropic mesophase behavior and the presence of enantiotropic behavior throughout the series might be connected to the bisazobezene core and the terminal groups that extend the molecules along their molecular axes which, increase thermal stability of the mesophases and anisotropy of molecular polarizability. The photoisomerization experiment indicates a decrease in intensities of the absorption bands for compound BA4 (BAn series). These show that the structure of the compounds does not have significant effect on the photoisomerization rate. This group of compounds have potential application in photonics more specifically, in reversible optical data storage, optical switching devices, optical computing and integrated optical devices for communication. The final series of compound 4-propyloxy-[4-biphenyloxyalkyl]-4`-(4-phenylazo)azobenzene for the dimer containing bisazobenzene mesogenic moiety and alkoxybiphenyl linked by flexible spacers (BAOnO.3 series) was prepared by reacting the 4-propyloxy-4-hydroxybiphenyl with 1-bromoalkyloxy-4`-(4-phenylazo)azobenzene. The synthesized compounds exhibited enantiotropic phase with dimer containing propyl, butyl and octyl as flexible alkyl spacers showing SmA and those with pentyl and hexyl spacers exhibited SmA and SmC phases respectively. The stability of the smectic layer depends on the spacer length for the compounds studied

    Synthesis And Characterization Of Isoflavone Derivatives Exhibiting Liquid Crystalline Properties [QD923. Y19 2008 f rb].

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    Sintesis dan kerja pencirian telah dilaksanakan ke atas enam siri hablur cecair klasik kalamitik yang berbentuk rod. Komponen tengah bagi kesemua halur cecair tersebut mengandungi 3-fenil-4H-4-on-benzopiran atau lebih dikenali sebagai isoflavon. Six series of classical rod-like, calamitic liquid crystals had been synthesized and characterized. These liquid crystals contained 3-phenyl-4H-4-one-benzopyran or generally known as isoflavone within the central moiety

    Gold liquid crystals in the XXI century

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    Producción CientíficaSince the first gold liquid crystal was described in 1986, much effort has been done to prepare new compounds bearing this property. The review deals with the last results obtained in this new century. Gold(I) has a strong affinity to give linear co-ordination and metal-metal interactions, which produce a rich supramolecular chemistry, and can promote the behavior as liquid crystal. Therefore, most liquid crystals are based on rod-like gold(I) compounds, while gold(III) liquid crystals are scarce. Calamitic and discotic mesogens have been reported, as well as chiral liquid crystals. Weak interactions such as H-bonds have also been used to obtain gold mesogens. Some of them exhibit additional properties, such as color, luminescence, and chirality. Luminescence has been reported, not only in the solid state or in solution, but also in the mesophase. This is relevant for applications in LEDs (Light Emitting Diodes), information storage, and sensors.Comisión Interministerial de Ciencia y Tecnología (Project CTQ2011–25137)Junta de Castilla y León (Proyecto VA302U13

    Synthesis and mesomorphic properties of a triphenylene-based discotic liquid crystal molecule with bisazobenzene at the periphery

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    A new triphenylene liquid crystal material with six rod-shape bisazobenzene moieties as the peripheral units has been synthesized and characterized by spectroscopic methods. The mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy and, X-ray diffraction. The mesogenic bisazobenzene was prepared by diazotization and coupling and subsequent etherification. The disc-shaped molecule, 2,3,6,7,10,11-hexakis[4`-(4-phenyazo)azobenzenehexyloxy]triphenylene was prepared by etherification of 1-bromohexyloxy-4`-(4-phenylazo)azobenzene on to the 2,3,6,7,10,11-hexahydroxytriphenylene nucleus. The presence of a nematic and smectic A mesophases was confirmed by optical textures and X-ray diffraction measurement.Keywords: Liquid crystal, Bisazobenzene, Triphenylene, Nematic phase, Semectic phase

    New liquid crystals in the series of 1, 3, 5-triazine compounds containing azobenzene at the peripheral arms

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    Novel liquid crystal materials whose molecular structures consist of disc-like 1,3,5-triazine unit as a central core and three rod-like azobenzenes as the peripheral arms unit has been prepared and characterized by spectroscopic methods, and X-ray diffraction. The Series of compounds were prepared by nucleophilic addition of the primary amino nucleophile to 1,3,5-triazine electrophilic ring via alkyl spacers in presence of potassium carbonate as hydrochloride acceptor. Differencial scanning calorimetry (DSC), polarizing optical microscopy and x-ray diffraction confirmed Smectic mesophase textures of the materials. Increase in the polymethylene spacer length influence the thermal and phase stability of the compounds studied
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