摘要:

Liquid crystal-polymer composites have been widely studied in the last ten years, both because of potential applications and to improve our understanding of the behavioural mechanisms involved. Although it cannot be exhaustive, this review describes recent advances in the field of liquid crystal-polymer composites. The preparation techniques as well as the operating principle and various applications of these materials are covered.

ISSN:0267-8292    

DOI:10.1080/02678299608032820

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Surface stabilized antiferroelectric liquid crystals are known to give multiplex-compatible greyscales by applying simple waveforms. Statistical variations of cell parameters are believed to be at the origin of this greyscale. In this work, an antiferroelectric model is applied to the study of cell statistical variations, aiming to identify the parameters whose variations may account for the experimental results obtained with these cells. It has been found that moderately small parameter variations, well within manufacturing tolerances, may lead to greyscales whose voltage range and shape are similar to those observed experimentally.

ISSN:0267-8292    

DOI:10.1080/02678299608032821

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

New mesomorphic side-on materials containing high birefringent groups (tolanes and naphthalenes) have been designed and synthesized. We present the synthesis and characterization of 6-(4-acryloyloxybutanyloxy)-1,4{bis-[2-(6-propanoxynaphthyl)]diethyn}benzoate and 6-(4-acryloyloxybutanyloxy)-1,4{bis-[2-(6-butanoxy)naphthyl)]}diethyn}benzoateand their corresponding polymers. The first monomer exhibits both enantiotropic smectic C and nematic mesophases, while the second monomer exhibits only a monotropic cholesteric mesophase. The effect of the second monomer on the birefringence of reflective cholesteric displays is reported.

ISSN:0267-8292    

DOI:10.1080/02678299608032822

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The synthesis of some aryl β-D-C-glycosides bearing long alkoxy chains (grafted on the carbohydrate moiety through the intermediate of an aromatic core) is described. Their mesomorphic properties (studied by microscopic observations under polarized light, DSC and X-ray diffraction) are presented.

ISSN:0267-8292    

DOI:10.1080/02678299608032823

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The orientational order of a ferroelectric mixture has been measured by proton NMR. The alignment of the mesogenic units is reflected in the splitting of the NMR signal into a doublet. Up to a cell thickness of 200 μm, it was possible to produce well-oriented layers in the bookshelf geometry by magnetic orientation of the substances in theB0-field. The angular dependences of the line width of the NMR signal on the tilt angle of the director have been calculated. A ferroelectric switching was detected by measuring the angular dependence of the line width in the switched state. The tilt angle and the orientational order parameter S of the bookshelf samples were estimated at various temperatures.

ISSN:0267-8292    

DOI:10.1080/02678299608032824

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Mixtures of a fluorescent liquid crystalline side chain polyacrylate and its corresponding ferroelectric monomer were studied by optical microscopy, DSC, X-ray and electro-optic techniques. For some of these mixtures we surprisingly found the emergence of the ferroelectric S*xphase, which is not exhibited by the single components. The crystalline phase of the monomer is completely suppressed by polymer concentrations above 25 per cent. The 50 per cent polymer-containing mixture shows a clear eutectic effect for the tilted phases and allows electro-optic switching close to room temperature, more than 40 K below the melting point of the monomer.

ISSN:0267-8292    

DOI:10.1080/02678299608032825

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Four series of tolane-based chiral liquid crystals that incorporate a tetrafluorophenyl moiety and a flexible oxymethylene linkage into the core have been synthesized. The mesomorphic properties have been studied by thermal polarizing microscopy. The relationship between the properties and chemical structures of all these target compounds, especially the influence of flexible oxymethylene linkage in core on the formation of mesophases, is also discussed in detail.

ISSN:0267-8292    

DOI:10.1080/02678299608032826

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Liquid crystals are known to possess large electronic optical non-linearities. Transient photoinduced absorption is not commonly applied to liquid crystals, but it is a powerful technique by which to examine the excited-state absorption (ESA) and hence the non-linear absorption of molecular systems. We show that measurements of this kind can give an insight into the dominant mechanisms of picosecond non-linear optical response in liquid crystals, and together with semi-empirical quantum chemical calculations appropriate assignments of the absorptions can be made. In particular, we report measurements of the transient ESA of the liquid crystal CB15 [4-(2-methylbutyl)-4-cyanobiphenyl] in its isotropic phase using femtosecond pump-probe spectroscopy in the wavelength range from 400 to 1000 nm. By pumping directly into the first excited state (S1) we identify at least four transient ESAs which contribute to the non-linear response up to a time of 1 ns after excitation. These features show a linear dependence with pump intensity. There also exists weak two-photon absorption (TPA) into S1at 650 nm, giving a similar ESA. Furthermore, we show that a semi-empirical quantum-chemical treatment of a single molecular unit of CB15 using the AMI Hamiltonian gives good agreement with the observed spectra, and implies that the dominant ESA in the picosecond regime can be attributed principally to singlet-singlet transitions from monomer units; but there is also a possible contribution to the ESAs by excimer absorption. On the time scale of our experiment we see no evidence of triplet-triplet absorptions, and we have also measured a fluorescence quantum yield of 20%.

ISSN:0267-8292    

DOI:10.1080/02678299608032827

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In a ferroelectric liquid crystal, a special type of phase-matching for optical second harmonic generation (SHG) is possible, where two counter-propagating fundamental waves create second harmonic waves at the edge of the selective reflection band. We compute the SHG intensity in such a situation and show that, at slight detuning from exact phase-matching, useful resonance enhancement can be obtained. A considerable amount of SHG also appears when the second harmonic frequency is in the reflection band, where the SHG wave is non-propagating.

ISSN:0267-8292    

DOI:10.1080/02678299608032828

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The preparation oftrans-2,5-disubstituted cyclohexan-1-ones from 3,6-disubstituted cyclohex-2-en-1-ones by reduction with hydrogen in the presence of palladium on carbon in a basic medium is described. The nature of the mesomorphic phases together with some physical properties of single compounds and of nematic mixtures comprising them are reported. Mesogens containing thetrans-2,5-disubstituted cyclohexan-1-one ring show a small negative dielectric anisotropy and a low birefringence.

ISSN:0267-8292    

DOI:10.1080/02678299608032829

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor