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2000 (1)
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1Author    J. Jadżyn, R. Dąbrowski, K. Glumiak, G. CzechowskiRequires cookie*
 Title    Shear Viscosity of the Homologous Series of wCHBT (n = 0 -f 12) in the Isotropic and Nematic Phases  
 Abstract    The paper presents results of shear viscosity measurements performed on nematogenic 4-(trans-4'-n-alkylcyclohexyl)isothiocyanatobenzenes (C"H 2n + i-CyHx-Ph-N=C=S, /iCHBT) in the isotropic (n = 0+ 12) and nematic (« = 4+12) phases. The viscosity measured in the nematic phase is, due to the flow alignment phenomenon, close to the Migsowicz T? 2 viscosity coefficient. An odd-even effect in the n dependence of the viscosity-activation energy is observed both in the nematic and isotropic phases of nCHBT. 
  Reference    Z. Naturforsch. 55a, 637—640 (2000); received April 19 2000 
  Published    2000 
  Keywords    Shear Viscosity, rcCHBT, Isotropic Phase, Nematic Phase 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0637.pdf 
 Identifier    ZNA-2000-55a-0637 
 Volume    55 
2Author    Klaus Praefcke, Dietmar Schmidt, HerrnF. Prof, BohlmannRequires cookie*
 Title    Erste flüssigkristalline Azulen-Derivate [1] First Liquid Crystal Azulene Derivatives [1]  
 Abstract    Various azulene derivatives as a new type of coloured liquid crystals have been syn-thesized. Their mesomorphic behaviour is described. Einführung Flüssigkristallanzeigen stellen, nicht zuletzt we-gen ihrer weitaus geringeren Stromaufnahme, eine erfolgversprechende Alternative zu den bisher ge-bräuchlichen, lichterzeugenden Displays dar. Wäh-rend letztere in fast jeder gewünschten Farbe her-gestellt werden können, ist eine farbige Flüssig-kristallanzeige bisher nur durch Dotierung des flüssigkristallinen Materials mit einem Farbstoff zu erzielen, da bis heute noch keine für technische Anwendungen geeigneten farbigen Flüssigkristalle bekannt sind. Eine Vielzahl von Dotierstoffen der unterschied-lichsten Strukturen sind kürzlich in einem Review über ,,Guest-Host"-Systeme zusammengefaßt wor-den [2]. Ergebnisse und Diskussion In Fortsetzung unserer Arbeiten auf dem Gebiet der flüssigen Kristalle haben wir nach den gelben 
  Reference    Z. Naturforsch. 36b, 375—378 (1981); eingegangen am 1. Dezember 1980 
  Published    1981 
  Keywords    Azulenes, Coloured Liquid Crystals, Nematic Phases 
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 TEI-XML for    default:Reihe_B/36/ZNB-1981-36b-0375.pdf 
 Identifier    ZNB-1981-36b-0375 
 Volume    36 
3Author    MagedA. Osman, M. A. OsmanRequires cookie*
 Title    Nematic Liquid Crystals with High Positive Dielectric Anisotropy * Nematic Liquid Crystals 1093 *>-®-CH-N-©-CN  
 Abstract    Alkylamino-and formyl alkylamino-cyano Schiff's base, biphenyl and phenylbenzoate liquid crystals were synthesized. The mesomorphic behaviour of these compounds is described. The introduction of the formyl group in the higher homologues lead to the disappearance of the mesophase. The alkylamino and formylalkylamino substituents are strong electron donating groups and lead to nematic phases with remarkably high positive dielectric anisotropy. Interest in electrooptical displays based on the twisted nematic effect [1] has lead to a growing demand for nematic liquid crystals with positive dielectric anisotropy. Non-polar or almost non-polar nematic compounds of the type 1 were found to possess a very small positive dielectric anisotropy (As = 0.05-0.5) [5-7], X =-CH= N-|21 , -C00-131,—N=N— |4| 1 Nematic phases of the Schiff's base and phenyl-benzoate type with larger A a were synthesized by A. Boiler [8, 9] through replacement of one of the alkyl groups by the cyano group which possess a larger dipole moment (—4 D). The remaining alkyl group on the other end of the molecule, which has a dipole moment of -f-0.3 D, was not changed. Recently, G. Gray [10] and R. Eidenschink [11] prepared analogous nematic phases of the biphenyl and phenyl cyclohexane types. All these compounds have A e values from 8 to 20 [12-14] which allow an operating voltage of 3 volts for a twisted nematic display. Since the threshold voltage and, correspond-ingly, the operating voltage is proportional to \J11A e, it is clear that new nematic liquid crystals with larger dielectric anisotropics are required if the operating voltage is to be substantially reduced. This can be achieved by replacing the remaining alkyl group with an electron donating substituent having a stronger dipole moment along the molecu-lar axis. The first attempt along this line was made by introducing the dimethylamino group (-(-1.6 D) * Reprint requests to Dr. M. A. Osman. 0340-5087/79/0800-1092/$ 01.00/0 at the other end of the benzyliden-aminobenzo-nitrile molecule, but this gave an isotropic com-pound melting at 183 °C [15]. The disappearance of the liquid crystalline properties is probably due to the high melting point of this compound and to the bulkiness of the dimethylamino group which lowers its clearing point. The aim of this work is to introduce the less bulky monoalkylamino group in molecules of type 1 and to study the effect of this substitution on their mesomorphic behaviour and on the magni-tude of the dielectric anisotropy. Results and Discussion N-(4-Methylaminobenzylidene)-4'-aminobenzo-nitrile (2) was prepared by condensing 4-methyl-aminobenzaldehyde with 4-aminobenzonitrile in bulk [16]. CH3HN-^)-cho+H2N-<Q>-CN-^CH3HN-Q>-CH-N^Q>-CN z The aldehyde was prepared by the Vilsmeier re-action [17]. 2"c> ~HjC :N CN H0 ~ H 3 CHN <> CHO Compound 2 melted at 163.1 °C and showed a monotropic nematic phase clearing at 138.0 °C. This confirmed that the disappearance of the meso-phase in the dimethylamino derivative was caused by the bulkiness of this group. However, the melting point of compound 2 is too high for practical applications and for conveniently measuring the dielectric anisotropy. The higher homologues of alkylaminobenzaldehyde and their Schiff's bases were therefore prepared in an attempt to lower the melting point. It seemed also of interest to 
  Reference    Z. Naturforsch. 34b, 1092—1095 (1979); received March 23 1979 
  Published    1979 
  Keywords    Liquid Crystals, Nematic Phases, High Positive Dielectric Anisotropy, Alkylamino-cyano-biphenyls, Alkylamino-cyano-phenylbenzoates 
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 TEI-XML for    default:Reihe_B/34/ZNB-1979-34b-1092.pdf 
 Identifier    ZNB-1979-34b-1092 
 Volume    34