| | 21 | 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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| default:Reihe_A/56/ZNA-2001-56a-0893_n.pdf | | | | Identifier
| ZNA-2001-56a-0893_n | | | | Volume
| 56 | |
| 23 | Author
| C. Forte, M. Geppi, C. A. Veracini | Requires 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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| default:Reihe_A/49/ZNA-1994-49a-0311.pdf | | | | Identifier
| ZNA-1994-49a-0311 | | | | Volume
| 49 | |
| 24 | 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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| default:Reihe_A/56/ZNA-2001-56a-0489.pdf | | | | Identifier
| ZNA-2001-56a-0489 | | | | Volume
| 56 | |
| 25 | Author
| B. Kirste | Requires 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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| default:Reihe_A/42/ZNA-1987-42a-1296.pdf | | | | Identifier
| ZNA-1987-42a-1296 | | | | Volume
| 42 | |
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