The temperature and frequency dependence of their dielectric constants have been investigated for two dimers consisting of swallow-tailed terminal groups connected via siloxane central parts of di erent length. The results have been compared with those of the respective monomer. The central part contributes in di erent ways to the static dielectric constants in the isotropic phase. From relaxation measurements, it can be concluded that the reorientation process about the short axis of the terminal groups is comparable with the respective process in monomers. The relaxation frequencies as well as intensities are almost unin¯uenced by the siloxane part which suggests a very¯exible structure of such dimers. Unfortunately, the maintenance of the antiparallel arrangement of swallow-tailed parts of the dimers could not be proved because of insu cient material for experimental work on the SA phase.
Measurements of the temperature and frequency dependence of dielectric constants have been performed for five homologues in the range 100 Hz -10 MHz. These substances exhibit a negative anisotropy of the dielectric constants and two relaxation regions (rotation of the molecules around the short resp. long axis) in the investigated frequency range. Even in the crystalline state dipolar reorientations are possible which have been interpreted as rotations of the alkoxy group. Changes of the static dielectric constants, relaxation frequencies and transition entropies are discussed as a measure of structural changes passing the several liquid crystalline phases.
Ausgehend von Δ10,11‐Undecensäure‐methylester wurde ein Verfahren zur Herstellung von Eicosandisäure‐(1,20) (C20), Tetracosandisäure‐(1,24) (C24) und Hexacosandisäure‐(1,26) (C26) ausgearbeitet.
Dielectric measurements on oriented liquid crystalline substances in the frequency range from 10 Hz to 100 kHz have been carried out. The static dielectric constant parallel to the director of both single components shows a strong decrease in relation to the expected value. In the case of the swallow-tailed compound this effect can be described by assuming an equilibrium between statistically and antiparallel oriented molecules. The second component has an extremly strong tendency to be antiparallel oriented. In the mixture of both a continuous change of the correlation was observed.Die eiektrischen Messungen an orientierten fliissig-kristallinen Substanzen wurden im Frequenzbereich yon 10 Hz bis 100 kHz ausgefuhrt. Die statische dielektrische Konstante parallel zum Direktor zeigt fur beide Komponenten eine starke Abnahme gegenuber dem erwarteten Wert. Im Fall der Schwalbenschwanzverbindung kann dieser Effekt durch die Annahme eines Gleichgewichtes zwischen statistischen und antiparallel orientierten Molekiilen beschrieben werden. Die zweite Komponente zeigt eine extrem starke Tendenz fur die antiparallele Orientierung. In der Mischung von beiden wurde eine kontinuierliche Anderung der Korrelation beobachtet.
Dielectric investigations on 4‐nitrobenzyl 2,5‐bis‐(4‐n‐hexyloxybenzoyloxy)‐benzoate A (10Hz – 100MHz) and a mixture of A and rodlike benzoates B (10Hz – 100kHz) reveal for A two main relaxation mechanisms in the liquid crystalline phases. The low frequency one connected with the reorientation around the short molecular axis shows in mixtures an anormal increase of the intensity with temperature. The unexpected behaviour of the static dielectric constants of A as well as the systematic change of the dielectric data in the mixture with B are interpreted by a systematic change of the antiparallel correlation of A in the short range.
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