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Determination of bulk values of twist elasticity coefficient in a chiral smectic C* liquid crystal

100%

Kuczyński W. , Nowicka K. , Dardas D. , Jeżewski W. , Hoffmann J.

Opto-Electronics Review

2010

tom Vol. 18, No. 2

176-180

A method is described for determination of bulk values of a twist elastic coefficient for smectic c-director in chiral smectic liquid crystals with a helical structure. The method was applied to 4-methylbutyloxy phenyl-4-octyloxy-benzoate (C8) in the chiral smectic C* phase. The measurements were performed using optical detection in a small deformation limit. In contrast to the usual methods, initial deformation of the helix (caused by strong surface interactions) was avoided by using homeotropic aligned thick samples. The critical temperature dependence of the measured coefficient was observed. The relation between the measured parameter and the smectic C order parameter is presented.

Retardation of Molecular Rotations Around the Short Axes at the Transition from the Isotropic to Different Liquid Crystalline Phases

100%

Urban S. , Gestblom B. , Dąbrowski R.

2002

tom Vol. 76 / nr 2-3

263-271

Results of the dielectric relaxation studies of several homologous series and some single compounds exhibiting different phase sequences (isotropic - nematic, isotropic - smectic A, C, B and E) are presented. Relaxation times characterizing the molecular rotations around the short axes in the isotropic and a given liquid crystalline (LC) phases were determined. Two quantities, the so-called retardation factor gLC-Is = _LC/_Is and the activation enthalpy are analyzed. In spite of drastic changes of the g-factors in the case of the isotropic - crystal-like smectic phase transitions (Sm B and E) in comparison with the isotropic - liquid-like phases (N, Sm A, Sm C) transitions the activation enthalpy does not depend practically on the LC phase. This will be discussed as resulting from the coupling of the rotational and translational motions.

Liquid Crystalline Properties of Azobenzenes : II. 4-Pentyloxy-, 4-Hexyloxy- and 4-Heptyloxy-4'-alkyloxyazobenzenes

75%

Galewski Z.

1999

tom Vol. 73, nr 9

1503-1511

Three new groups of unsymmetrically alkyloxyazobenzenes are presented for the alyloxy chain length up to octadecyloxy. In each investigated compound the liquid crystalline mesophase, mainly nematic, was found.

Rheological properties, structure and thermal behavior of liquid crystalline copolyester

75%

Levchenko A. A. , Abdullaev K. M. , Antipov E. M. , Kulichikhin V. G. , Stamm M.

Applied Mechanics and Engineering

1999

tom Vol. 4, no spec.

289-296

Rheological properties and thermal behavior of a copolyester (CPE) prepared as high oriented fibers from PET, hydroxybenzoic, terephthalic acids and hydroquinone (40:20:20:20 mol %) in a temperature range of 30-350oC have been investigated by capillary viscosimetry, WAXS, SAXS and DSC. The copolyester under study can be characterized by an existence of two temperature regions with various shapes of flow curves. Different values of flow activation energies in the low and high temperature regions were determined. This material revealed a prominent dependence of viscosity on a residence time at 240oC and its absence at higher temperatures. It has been found that the non-crystalline structure of as-spun fibers can be identified as a LC smectic state with non-periodic layers. The crystalline phase (~8 %) coexists with LC one. A first-order phase transition takes place at 220oC, related to a presence of block sequences of PET that can be formed during the synthesis. The remaining part represents solid crystalline phase melting at 293oC. This phase plays role of net junctions that prevent the actual flow of soften CPE. Therefore, in a temperature range 240-250oC a pure slippage and a superposition of the flow and slippage ( 255-280oC) take place. Only at T>290oC a real flow proceeds.

Liquid Crystalline Properties of 4-Methyl-, 4-Ethyl- and 4-Propyl-4'-alkyloxyazobenzenes

75%

Zienkiewicz J. , Galewski Z.

2002

tom Vol. 76 / nr 2-3

359-366

Liquid crystalline properties of 4-methyl-4_-alkoxyazobenzenes (azo-1-n), 4-ethyl-4_- alkoxyazobenzenes (azo-2-n) and 4-propyl-4_-alkoxyazobenzenes (azo-3-n) are described. For these three homologous series, temperatures and enthalpies of phase transitions and the types of mesophases are presented. The influence of the alkoxy chain length on the sequence of mesophases, temperatures of the phase transitions and the entropy effects are discussed.