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21Author    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 
22Author    V. I. StepanovRequires cookie*
 Title    Comment on the Osipov-Terentjev Calculation of the Viscosity of Liquid Crystals  
 Abstract    The calculation of the viscosity of liquid crystals based on the rotational diffusion approximation recently reported by Osipov and Terentjev [1 a] is critically examined. It is shown that the main result of their treatment -the evaluation of the activational exponent -arises from the neglect of the second derivative of the distribution function with respect to the azimuthal angle in the Fokker-Planck equation. The correct asymptotic formula for the rotational viscosity coefficient is derived. 
  Reference    Z. Naturforsch. 47a, 625—626 (1992); received August 8 1991 
  Published    1992 
  Keywords    Liquid crystal, Viscosity coefficient, Rotational diffusion, Fokker-Planck equation, Energy barrier 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0625_n.pdf 
 Identifier    ZNA-1992-47a-0625_n 
 Volume    47 
23Author    C. Forte, M. Geppi, C. A. VeraciniRequires cookie*
 Title    Study of the Molecular Dynamics from Deuterium Zeeman and Quadrupolar NMR Relaxation of 4,4'-di-n-Heptylazoxybenzene in the Nematic and Smectic A Phases  
 Abstract    The deuterium spin-lattice (T1Z) and quadrupolar (r iQ) relaxation times of the liquid crystal 4,4'-Heptyl-azoxybenzene (HAB), deuterated on the aromatic rings and the first methylene group of the chains, have been measured by means of the Jeener-Broekaert pulse sequence at two different frequencies (10 and 46.04 M Hz) and throughout the nematic and the smectic A phase. By applying suitable models, we have determined rotational and reorientational diffusion coefficients and evalu­ ated the contribution of the different m otions (internal, molecular and collective) to the relaxation. In particular we have found a non negligible contribution from order director fluctuations. A comparison between the Tlz and Ti Q measurements performed by means of Jeener-Broekaert and Wimperis pulse sequences is also shown. 
  Reference    Z. Naturforsch. 49a, 311 (1994); received August 16 1993 
  Published    1994 
  Keywords    Liquid crystal, Deuterium N M R, M olecular dynamics, Deuterium relaxation, Director fluctuation 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0311.pdf 
 Identifier    ZNA-1994-49a-0311 
 Volume    49 
24Author    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 
25Author    B. KirsteRequires cookie*
 Title    EPR and ENDO R Investigations of a Cholestane Spin Probe in Liquid Crystals  
 Abstract    A detailed EN D O R study o f anisotropic proton hyperfine shifts in the nitroxide spin probe 3-doxylcholestane (CSL) in liquid-crystalline solution is described. The data are interpreted by means o f theoretically calculated proton hyperfine tensors (M cConnell-Strathdee-Derbyshire treatment), providing an independent check o f the ordering matrix. The orientational order and the dynamic behavior o f the nematic and smectic phases o f the liquid crystals (40,6), (50,6), and 8CB are investigated by EPR using CSL and phenalenyl as spin probes. 
  Reference    Z. Naturforsch. 42a, 1296—1304 (1987); received August 8 1987 
  Published    1987 
  Keywords    EPR, EN D O R, liquid crystal, order parameters, sm ectic phase 
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 TEI-XML for    default:Reihe_A/42/ZNA-1987-42a-1296.pdf 
 Identifier    ZNA-1987-42a-1296 
 Volume    42