| 2 | Author
| I. D. Ierking1, F. G. Ießelm Ann1, P. Zugenm, H. R2, H. Z. Aschke2, W. Kuczynski3 | Requires cookie* | | Title
| The Origin of the Helical Twist Inversion in Single Component Cholesteric Liquid Crystals  | | | Abstract
| The cholesteric twist inversion by temperature variation o f a single com ponent thermotropic liquid crystalline system was experimentally investigated and is explained by the partial twisting power model, evaluating the temperature dependent pitch o f five different configurations of a benzoic acid biphenyl ester with two chiral centers. The temperature dependence o f the twisting power and the cholesteric pitch for several stereoisomeric com pounds can in first approximation be predicted by the partial twisting powers of the individual chiral centers determined from the partially racemic configurations. | | |
Reference
| Z. Naturforsch. 49a, 1081—1086 (1994); received August 12 1994 | | |
Published
| 1994 | | |
Keywords
| Liquid crystal, Chirality, Cholesteric mesophase, Twist inversion | | |
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| default:Reihe_A/49/ZNA-1994-49a-1081.pdf | | | Identifier
| ZNA-1994-49a-1081 | | | Volume
| 49 | |
3 | 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 | |
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