Showing papers by "Jan Jadżyn published in 1994"

Order Parameters in Some Nematics Determined from Optical Spectroscopy

Abstract: The measurements of the polarized absorption and fluorescence spectra of stilbene-derivative guest molecules dissolved in some nematic liquid crystals have been used for studies of the long-range orientational order in thin aligned samples. The temperature dependence of the order parameters (P 2) and (P 4) has been investigated. The influence of the molecular structure on the orientational order in nematics has been discussed.

Dielectric Anisotropy in Nematic of p-Cyano-p'-Alkyl-Phenylcyclohexanes

Abstract: Anisotropy of static electric permittivities of the homologous series of p-cyano-p'-alkylphenylcyclohexanes (PCH) have been measured as a function of temperature in isotropic and nematic phases The mean square effective dipole moment components along the principal directions of a liquid crystal have been determined The Kirkwood correlation factors g(i), obtained from Maier and Meier equations, exhibit the odd-even alteration within the studied series The g-factors values have been interpreted in terms of an anti-parallel association

Dielectric Relaxation in Nematic and Isotropic Phases of 4-(trans-4'-n-Propylcyclohexyl) isothiocyanatobenzene

Abstract: Abstract The results o f a dielectric relaxation study (in the frequency region from about 1 kHz to 1 GHz) of the liquid crystalline title com pound (C3H7-Cyhx-Ph-NCS , 3-CHBT) in the isotropic and the nematic phase (measurements with electric field parallel to alignment) are presented. The spectra of both phases can be described by two relaxation processes of Debye-type, possibly related to rotation around the long and short molecular axes.

Variability of the Smectic a Layer Spacing and Dielectric Properties in the Homologous Series of 4-Isothiocyanatophenyl 4- (Trans-4-Alkylcyclohexyl) Benzoates

Abstract: The homologous series of 4-isothiocyanatophenyl 4-(trans-4-alkylcyclohexyl)benzoates (with n-alkyl chain from ethyl to dodecyl) were synthesized and their phase transition temperatures and enthalpies, smectic layer spacing and dielectric permittivity were measured. It was observed that the smectic A, layer spacing is expanding from d/l ∼ 1 to d/l ∼ 1.1 when the alkyl chain increases from butyl to dodecyl. It was proposed to term the smectic A1 with d/l > 1 as the enhanced smectic A1 (Ale).

Dielectric Properties of 4-Cyanobiphenyl in 1,4-Dioxane Solution

Abstract: Abstract The static and dynamic dielectric properties o f the title system are reported for a concentration series from about 8 mmol/1 up to 2.3 mol/I at 20 °C. The apparent moment (4.2 D , extrapolated to infinite dilution) decreases with increasing concentration, the relaxation time increases proportional to viscosity, that is, somewhat steeper than usually observed. Com parison with other molecules suggests that these features are mainly due to the high dipole moment rather than being specifically related to the prolate shape o f the molecule. The broadening o f the spectrum toward the high frequency side, on the other hand, may be due to the molecular shape.

Elastic properties of n-octyloxycyanobiphenyl

Abstract: The temperature's behaviour of the splay and band elastic constants for n-octyloxycyanobiphenyl (8-OCB) has been studied. The constants have been determined on the basis of threshold values BO and Uo resulting from the Frederiks transitions in magnetic and electric field, respectively. The K11 and K33 show the pretransitional nematic-smectic A effect.