摘要:

A well-controlled, reproducible alignment with or without a pretilt angle is a basic need for the development of any kind of liquid crystal display. We have built an optical set-up based on the crystal rotation method. With this system we can measure the pretilt angle in nontwisted liquid crystal samples. Presentation of the experimental set-up and first results of these measurements (obtained with a precision of 0.3) are given for several compounds and alignment layers.

ISSN:0267-8292    

DOI:10.1080/026782997209559

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Liquid crystalline side group copolymers containing cholesteryl and S-(-)-chloropropionyloxybiphenyl groups were synthesized and investigated by size exclusion chromatography, 1H NMR spectroscopy, polarization microscopy, X-ray diffraction and differential scanning calorimetry. The spacer of the cholesteryl-containing side groups was changed by the substitution of two methylene groups by ether groups. The existence of a cholesteric phase on copolymerization of two monomers containing chiral tail groups, from which the homopolymers exhibit only smectic phases, could be observed. This cholesteric phase only exists over a narrow range of copolymer composition. The temperature dependence of the reflection wavelength for the cholesteric phase was determined. For the cholesteryl-containing homopolymer, an SA bilayer phase was observed, whereas the S-(-)-chloropropionyloxybi2 phenyl homopolymer showed a higher ordered SB phase below an SA monolayer phase. The layer periodicities of the SA phases of the copolymers depend on the composition. The substitution of two methylene groups of the spacer by ether groups led to disappearance of the cholesteric phase. Simultaneously, over a small range of copolymer composition a biphasic region was obtained.

ISSN:0267-8292    

DOI:10.1080/026782997209568

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

IR spectroscopy was used to study the orientation and mobility of different molecular segments in a side chain ferroelectric liquid crystalline polymer (FLCP) in the book-shelf geometry. It was directly shown that the tilt angles for the mesogenic units and the spacers are different. The data obtained allowed us to construct a detailed model of segmental orientation in the SC phase for this FLCP. This model is consistent with the ‘zigzag’ model for tilted smectic phases. The rotational bias of carbonyl bonds is also confirmed and a possible orientation function for the carbonyl group is discussed. Time-resolved step-scan FTIR spectroscopy enabled us to follow the intra- and inter-molecular response of the FLCP to an external electric field with a time resolution of 5 mus. It was detected that mesogenic moiety, spacer and backbone take part in the reorientation process. The time responses of different molecular segments are similar on the time scale of a few hundred microseconds.

ISSN:0267-8292    

DOI:10.1080/026782997209577

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

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 different length. The results have been compared with those of the respective monomer. The central part contributes in different 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 uninfluenced by the siloxane part which suggests a very flexible structure of such dimers. Unfortunately, the maintenance of the antiparallel arrangement of swallow-tailed parts of the dimers could not be proved because of insufficient material for experimental work on the SA phase.

ISSN:0267-8292    

DOI:10.1080/026782997209586

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

An achiral semiperfluorinated chain has been introduced into classical phenyl benzoate mesogenic moieties in which the other terminal chain is chiral. The consequences of this modification on the mesomorphic properties are discussed. At a low fluorination extent, the smectic A phase is strongly favoured, while at high extents of fluorination the chiral smectic C phase is enhanced. The direction of the central ester linkage influences not only the phase diagram, but also the spontaneous polarization induction power.

ISSN:0267-8292    

DOI:10.1080/026782997209595

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor