摘要:

The reflection spectrum for visible light is examined for the cholesteric and blue phases of chiral CE6. Pronounced side band oscillations are observed. The Bragg wavelength for total reflection diverges towards the smectic phase with an exponent v = 0·71±0·05. Going from the cholesteric phase toBPI, the lattice parameter increases by (2)1/2. Evidence is given for the existence of a long-lived supercooled blue phase (BPS).

ISSN:0267-8292    

DOI:10.1080/02678299308027738

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The optical rotation of a mixture of 60 per cent of chiral and 40 per cent of racemic CE6 as an 18 μm thick sample placed between glass plates treated with PI has been measured. This mixture exhibits one blue phase (BP1) on heating over a temperature range of about 0·1°C. On cooling the sample on the other hand, the BP region is expanded to 0·6°C and is divided into two regions. One region (BP1) (of range about 0·38°C below the isotropic–blue phase transition) shows two Bragg wavelengths which increase with decreasing temperature. For the second region (BPS) (of range about 0·22°C above the cholesteric–blue phase transition), one Bragg wavelength decreases with decreasing temperature, and a third Bragg wavelength appears. At constant temperature both phases remained stable for a period of several days.

ISSN:0267-8292    

DOI:10.1080/02678299308027739

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A scanning adiabatic calorimetric technique has been used to study the thermal properties of the chiral and racemic liquid crystal CE6 and the phase diagram covering the cholesteric phase, the three blue phases and the isotropic phase. The purpose of this investigation is to study thermal properties of liquid crystals as a function of chirality, while all other parameters remain constant. Results for the temperature and the chirality dependence of the enthalpy and of the heat capacity are reported. The latent heats between the cholesteric phase and BPI and between the different blue phases change slightly as a function of the chirality. The total heat of transition at the isotropic phase boundary is independent of the chirality, but with decreasing chirality, we observe a large increase in the latent heat and, correspondingly, a decrease in the pretransitional contribution. These experimental facts are in qualitative agreement with the predictions of a Landau–de Gennes theory for blue phases.

ISSN:0267-8292    

DOI:10.1080/02678299308027740

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The influence of molecular order as well as of orientation of charge carrier units on photoconductivity has been investigated for the liquid crystal photoconductors H5T (1), thiadiazole (2) and oxadiazole (3). The discotic H5T (1) and both smectic systems2and3exhibit a higher photocurrent in the highly ordered mesophase than in the polycrystalline or isotropic state. For1, results concerning charge carrier transport mechanism and Dember effect are given indicating an electronic charge transport comparable with the one known for single crystalline anthracene.

ISSN:0267-8292    

DOI:10.1080/02678299308027741

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We present the synthesis and a description of the physical properties of several organic dyes containing stilbene as well as azomethine groups. The preparations of all compounds started from a common precursor, 4-amino-4′-nitrostilbene, followed by condensation with aromatic aldehydes. The mesomorphic properties and spectroscopic data were established using polarizing microscopy, DSC measurements, X-ray and UV/Vis spectroscopy. Three of the compounds showed enantiotropic smectic phases, two of them highly ordered SEand SBphases, and a nematic phase. In addition quantum chemical calculations concerning the electronic properties were carried out.

ISSN:0267-8292    

DOI:10.1080/02678299308027742

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Seventeen esters, derived from 4-n-alkoxy-3-fluorophenols and 4-(5-n-alkyl-2-thienyl)benzoic acids, have been prepared and their liquid crystal transition temperatures determined by thermal optical microscopy. On cooling the isotropic liquid, the SA-SC-SAsequence of phases reported for the octyloxy-octyl and octyloxy-nonyl esters has been observed for certain other homologues, principally members of the 4-(5-n-nonyl-2-thienyl)benzoates. For these compounds, the temperature range of occurrence of the intermediate SCphase decreases as the length of the alkoxy chain increases (for the hexyloxy-nonyl to dodecyloxy-nonyl esters) and the Scphase is absent for the tetradecyloxy-nonyl homologue.

ISSN:0267-8292    

DOI:10.1080/02678299308027743

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A novel liquid-crystalline polymer, the toluene-4-sulphonyl urethane of hydroxypropylcellulose (TSUHPC), was prepared through chemical modification of hydroxypropylcellulose (HPC) ofMw= 60000 g mol−1. The resulting polymer was characterized by infrared spectroscopy, differential scanning calorimetry (DSC) and polarizing microscopy. It was found that thermotropic liquid crystal phases are formed between about 60°C and 110°C. Concentrated solutions of TSUHPC in acetone andN,N-dimethylacetamide exhibit cholesteric behaviour, at room temperature. When approaching the lyotropic mesophase to solid transition, either by cooling or by solvent evaporation, very interesting arborescent structures of a seemingly fractal nature may be observed, depending on the kinetics of the transition. A banded texture can be observed when the polymer is sheared near the transition to the isotropic phase.

ISSN:0267-8292    

DOI:10.1080/02678299308027744

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A new chiral alcohol, 2(S)-[2(S)-methylbutyloxy]propanol (3), containing two chiral centres has been synthesized from ethyl lactate and (S)-1-iodo-2-methylbutane. It was used as a chiral building block for the preparation of ferroelectric liquid crystal materials. Several of the new materials exhibit an enantiotropic S*cphase with a wide temperature range. The results indicate that the molecular structure of3is useful for synthesizing ferroelectric liquid crystal materials.

ISSN:0267-8292    

DOI:10.1080/02678299308027745

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Three new homologous series of mesogens containing three rings in the main structure and a lateral aromatic branch have been synthesized. When the lateral aromatic branch is attached to the middle ring, monotropic phases are observed, and there is a strong tendency to form the smectic C phase. When the lateral aromatic branch is attached to an outer ring, the compounds possess purely enantiotropic nematic phases. The terminal alkoxy chain in the outer ring which has a lateral aromatic substituent can be replaced by a rigid group without disturbing the large nematic range. Selective introduction of a particular substitutent may be useful for the construction of devices possessing desirable characteristics such as non-linear optical properties.

ISSN:0267-8292    

DOI:10.1080/02678299308027746

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The 5-n-alkyl-2-[4-(n-alkoxy)phenyl]pyrimidmes are essential components of most commercial chiral smectic C mixtures for electrooptic display devices based on ferroelectric effects. This is due to their generally relatively low melting points, enantiotropic, relatively wide range smectic C mesophases, low viscosity and ease of preparation. An unsaturated carbon–carbon double bond has now been introduced into the terminal alkoxy chain of the 5-n-alkyl-2-[4-(alkoxy)phenyl]pyrimidines to produce the corresponding alkenyloxy substituted derivatives. The position and nature (E/Z) of the double bond has been varied systematically and the effect on the liquid crystal transition temperatures studied. A number of homologous series of the most interesting alkenyloxy substituted materials has been prepared and evaluated. The position and nature (E/Z) of the double bond changes the conformation of the alkenyloxy chain substantially. This can result in significantly higher smectic C transition temperatures for compounds with atransdouble bond (E) at an even number of carbon atoms from the molecular core. Significantly lower transition temperatures (including the melting point) are observed for materials with acisdouble bond (Z) at an odd number of carbon atoms from the molecular core. Comparisons with the corresponding alkoxy substituted materials (i.e. without a double bond) are made.

ISSN:0267-8292    

DOI:10.1080/02678299308027747

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor