ZfN: Search Results

1	Author	H. Schmalfuss, W. Weissflog, A. Würflinger3, S. Masberg3, G. M. Schneider3	Requires 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

2	Author	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. Ja	Requires 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

3	Author	Stanislaw Urban, Albert Wiirflinger3	Requires 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