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'Liquid crystals' in keywords Facet   Publication Year 2001  [X]
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1Author    H. Schmalfuss, W. Weissflog, A. Würflinger3, S. Masberg3, G. M. Schneider3Requires cookie*
 Title    Thermodynamic Measurements on Selected Liquid Crystals at Normal and Elevated Pressures  
 Abstract    Densities have been determined for two 5-n-alkyl-2-(4-isothiocyanatophenyl)-l,3-dioxanes (6DBT, 10DBT), 4-n-tetradecyl-4'-cyanobiphenyl (14CB), 4-n-octyl-4'-thiocyanatobiphenyl (8BT) and two laterally aryl-branched mesogens 4-cyanobenzyl 5-(4-n-octyloxybenzoyloxy)-2-undecyloxybenzoate (4CNOUB), 3-cyanobenzyl 2,5-bis(4-n-octyloxybenzoyloxy)benzoate (3CN-BOB). The densities have been measured in the isotropic, nematic (only 3CNBOB) and smectic phases with a vibrating tube densimeter. The densities decrease with increasing alkyl chain length within a homologous series. Furthermore the enthalpy changes accompanying the phase transitions have been determined by DSC. 
  Reference    Z. Naturforsch. 56a, 262—266 (2001); received December 5 2000 
  Published    2001 
  Keywords    Specific Volumes, Density, DSC, Liquid Crystals, Thermodynamics 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0262.pdf 
 Identifier    ZNA-2001-56a-0262 
 Volume    56 
2Author    A. K. Urbatov, P. Janik, A. D. Ro, Zd-R Zo Sk, S.J R Zo Sk, M. Paluch, P. M. Alik, J. Z. Io Ło, J. JaRequires cookie*
 Title    Universal Scaling of Alpha Relaxation in Complex Liquids  
 Abstract    A plot is given, showing the result of a scaling analysis of dielectric loss curves containing, apart from low molecular glass former data (glycerol, dibutyl phtalate), also loss curves of the following liquid crystalline materials, mostly in the iso­ tropic phase: 4-(2-methylbutyl)-4'cyanobiphenyl (5*CB, supercooled isotropic phase), 4-cyano-4-n-alkyl biphenyls (nematogens 5CB and 8CB, isotropic phase), 4-(4-cyano-4-butylcyclohexyl)-4'-octylbiphenyl (laterally substituted nema-togen, isotropic phase), and 4-n-alkyl-4'-isothiocyanatobiphe-nyl (5 and 10 BT, isotropic and SmE phases). The plot applies the scaling formula originally proposed for glassforming, super­ cooled liquids [Dendzik et al.7]. The result supports the recent suggestion that dielectric relaxation in the isotropic phase of nematogens may show some features typical for "glassy" mate­ rials. 
  Reference    Z. Naturforsch. 56a, 893—894 (2001); received September 21 2001 
  Published    2001 
  Keywords    Complex Liquids Supercooled Liquids, Liquid Crystals, Dielectric Loss Curves, Universality 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0893_n.pdf 
 Identifier    ZNA-2001-56a-0893_n 
 Volume    56 
3Author    Stanislaw Urban, Albert Wiirflinger3Requires cookie*
 Title    DTA and Dielectric Studies under Pressure of a Smectogen Substance with a Strong Perpendicular Dipole Moment  
 Abstract    The phase diagram of a substance with two CN groups attached to the benzene ring at lateral posi­ tions (CNCN) has been obtained with differential thermal analysis (DTA). The pressure range of the smectic A phase is limited, resulting in a triple point (Cr, SA, L) at 135 MPa and 371 K. However, the SA-phase exists also above the triple point as a metastable phase. The transverse relaxation times rx were obtained from the dielectric spectra measured for several isotherms as a function of pressure with­ in the SA-phase of CNCN. The activation volume, A#Vj_ = RT (d In = (52 ± 3) cm3/mol is larg­ er than A Vj|, recently derived from the pressure dependence of the longitudinal relaxation times for other substances in the SA-phase. It is concluded that due to steric hindrances made by the cyano groups the molecular rotations around the long axes become strongly slowed down by pressure and the smec­ tic phase disappears 
  Reference    Z. Naturforsch. 56a, 489—4 (2001); received April 23 2001 
  Published    2001 
  Keywords    Liquid Crystals, Smectic A, DTA, Phase Diagram, Dielectric Relaxation, High Pressure 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0489.pdf 
 Identifier    ZNA-2001-56a-0489 
 Volume    56