摘要:

Liquid crystalline main chain polysiloxane esters have been formed by reacting bis[4-(ω-alkenyloxy)benzoic acid]esters containing 1,4-phenylene, 4,4′-biphenyldiyl, 2,7-fluorenediyl, and 2,7-fluorenonediyl units with, α,ω-di-H-oligo(dimethylsiloxane)s. The chemical structure has been confirmed by elemental analyses, IR,1H-NMR and13C-NMR spectroscopy. Molecular weights have been measured by GPC. The thermal behaviour has been studied by polarising microscopy and by DSC. In general the phase transitions are lower with a decreasing length of the alkylene spacers and with an increasing number of siloxane units within the spacer while they increase with magnification of the mesogenic groups. X-ray diffraction measurements for one polymer confirmed the type of the liquid crystalline phases (N, SC, SF). Deuteration has no influence on the thermal behaviour.

ISSN:1058-725X    

DOI:10.1080/10587259808047102

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Dielectric constant (ε′) and electrical conductivity ([sgrave]) of the binary mixtures of cholesteryl pelargonate (ChP) and nonyloxybenzoic acid (NOBA) of different concentrations have been measured in the frequency range of 100 Hz to 10 MHz from room temperature to 150°C both in planar and homeotropic alignments. These mixtures do not show the dielectric dispersion upto 10 MHz. Dielectric constants parallel and perpendicular to helical axes (ε′∥and ε′⊥) and the dielectric anisotropy (Δε′ = ε′∥- ε′⊥) have been determined in different mesophases. Dielectric anisotropy (Δε′) of the mixtures changes sign from negative to a positive value for NOBA concentrations above 75 mole %. From the measured frequency dependent conductivity [sgrave](f), d.c. conductivity [sgrave](dc) has been obtained using the universal power law equation. Activation energy (Wa) of the d.c. conduction process has been determined in different mesophases.

ISSN:1058-725X    

DOI:10.1080/10587259808047103

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this paper, we report an original fringe pattern observed in the light scattered by a nematic liquid crystal confined in a capillary. Using a fiber properly tapered, it has been possible to obtain a very well collimated and narrow beam that has been driven in a capillary filled with a nematic liquid crystal. This source beam is scattered by the liquid crystal and this scattered light exhibits a fringe pattern. This pattern is experimentally studied and an explanation is given. It is shown how the pattern is correlated with the liquid crystal structure, and in turn how this pattern can be used as a structure explorer.

ISSN:1058-725X    

DOI:10.1080/10587259808047104

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this work we present a structural study of the smecticC(SC)and columnar (Colh) liquid-crystalline phases exhibited by a biforked molecule. This study was performed by means of dilatometry and X-ray diffraction measurements performed at different temperatures. Following these measurements, molecular packing within lamellar and columnar mesophases of this compound is discussed; finally, a mechanism for the lamellar-columnar transition is proposed.

ISSN:1058-725X    

DOI:10.1080/10587259808047105

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Dielectric and electro-optical properties of the various antiferroelectric and ferrielectric smectic phases of two compounds of the homologous series MHPnCBC (n= 8,9) have been investigated. MHP9CBC exhibits an unidentified chiral induced SmC subphase (denoted by SmCx*) and shows the phase sequence Cr - SmIA* - SmCA* - SmCγ* - SmC SmCx* - SmC SmCx* - SmA - I. The electro-optical and dielectric properties of the SmC SmCx* phase of MHP9CBC differ distinctly from that of the SmC SmCα* as well as the SmC SmCγ* phase. The electric field - temperature phase diagram was obtained by two methods, measurement of the apparent tilt angle as well as the dielectric loss. The results of both methods are in good agreement. For both compounds a field induced ferrielectric state is observed in a broad temperature range (≊ 10 K) of the SmC SmCA*−phase.

ISSN:1058-725X    

DOI:10.1080/10587259808047106

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A series of new rodlike organometallic complexes based on the β-diketone ligands with terminal metal have been synthesized. The mesomorphism of the ligands and complexes has been investigated using DSC and polarizing microscopy. Most of the complexes display nematic mesogenic behavior identically with that exhibited by ligands. The effect of the carbon number of the terminal chain on the mesomorphism is discussed.

ISSN:1058-725X    

DOI:10.1080/10587259808047107

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The possibility of high-power IR-radiation modulation by cholesteric-nematic phase transition in LC is discussed.

ISSN:1058-725X    

DOI:10.1080/10587259808047108

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The optical transmission of antiferroelectric liquid crystal layers is non-trivial. For optical wavelengths we average the dielectric tensors. The aim is to provide a geometrical way for this averaging. By a thorough mathematical analysis, we are able to construct the representation ellipsoid for the final ε-tensor in most cases. In this way, we can easily predict the axes and indices of refraction of the structure. Especially the molecular states that occur during the hysteresis switching behaviour are studied.

ISSN:1058-725X    

DOI:10.1080/10587259808047109

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper describes syntheses and properties of some members of 4-(4-alkoxyphenoxycarbonyl)phenyl 3-alkoxy-4-cyanobenzoates. The ethoxy and propoxy groups at the adjacent position of the cyano one are unfavorable for the formation of a smectic A phase and the long alkoxy groups such as butoxy, pentyloxy, and hexyloxy ones facilitate the formation of a smectic C phase. The characterization and molecular arrangement of the smectic C phase were made by a differential scanning calorimeter, microscopic observation, and small-angle X-ray diffraction examination, and the roles of the alkoxyl group at the adjacent position of the cyano group on the mesomorphic properties are discussed.

ISSN:1058-725X    

DOI:10.1080/10587259808047110

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Liquid crystal (LC) waveguide claddings with different boundary couplings have been electrically switched. It is observed that the cut-off voltage of guided modes significantly decreases with decreasing the azimuthal surface anchoring energy of the LCs. An LC-covered planar lightwave modulator with low driving voltage of 12 volts is demonstrated by controlling the surface azimuthal anchoring energy of LC claddings.

ISSN:1058-725X    

DOI:10.1080/10587259808047111

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor