摘要:

The half-leaky guided mode technique for quantifying thin optical layers is here combined with a data fitting routine based on a genetic algorithm to provide an immensely powerful procedure for detailing the director profile in liquid crystal cells. This approach not only provides a full description of the optical parameters of the cell, but also gives quantitative uncertainties in these parameters. It is tested here, first by fitting to theoretically produced data and then applied to real experimental data.

ISSN:0267-8292    

DOI:10.1080/026782997209360

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We have synthesized and studied trisbenzocyclononenes carrying six chiral side chains. They are pyramidic shaped molecules exhibiting columnar mesophases. The optical and electrooptical effects of this chiral pyramidic compound have been studied. A homeotropic alignment of the columnar phase was achieved by cooling the film between plates treated with octadecyltriethoxysilane in the presence of a d.c. field. A transient optical effect was observed with these films on electric field reversal. Simultaneously there was a peak in the time dependence of the electric current flowing through the sample. The observations indicate that the columnar phase is ferroelectric with the polarization parallel to the optical axis. A few degrees below the clearing point, the time for polarization reversal is in the range of seconds and the magnitude of the polarization is 10 mC m. An electroclinic effect was observed for films with fan textures. 2

ISSN:0267-8292    

DOI:10.1080/026782997209379

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A perturbed hard-sphere-chain (PHSC) equation of state is presented to compute nematicisotropic equilibria for thermotropic liquid crystals, including mixtures. The equation of state consists of an isotropic term and an anisotropic term given by the Maier-Saupe theory whose contribution disappears in the isotropic phase. The isotropic contribution is the recently presented PHSC equation of state for normal fluids and polymers which uses a reference equation of state for athermal hard-sphere chains and a perturbation theory for the squarewell fluid of variable well width. The PHSC equation of state gives excellent correlations of pure-component pressure-volume-temperature data in the isotropic region and, combined with the Maier-Saupe theory, correlates the dependence of nematic-isotropic transition temperature on the pressure. Theory also predicts a nematic-isotropic biphasic region and liquid-liquid phase separation in a temperature-composition diagram of binary mixtures containing a nematic liquid crystal and a normal fluid or polymer. Theory and experiment show good agreement for pure fluids as well as for mixtures.

ISSN:0267-8292    

DOI:10.1080/026782997209388

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A TN structure is characterized by a twist angle (Theta) and a Deltand value, where Deltan is the refractive index anisotropy value of a liquid crystal material and d is the TN cell gap value. Two new methods for measuring these values have been proposed. One is to determine only the Deltand value by rotating the TN cell for a known Theta value. The other is to determine the Deltand value and the Theta value by rotating the analyser. After analysing these measurement methods, the Deltand value, or the Deltand value and Theta can be determined graphically. These methods can easily be applied to automatic measurement systems.

ISSN:0267-8292    

DOI:10.1080/026782997209397

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

An a.c. calorimetric study has been carried out on octylphenylthiolpentyloxybenzoate (8S5) in three silica aerogels with mass densities rho 0.08, 0.17 and 0.36g cm. Results for the least porous aerogel (rho 0.36) are completely consistent with those reported previously for 8CB in the same aerogel. Freezing of 8S5 damaged the more porous rho 0.08 and 0.17 aerogels by creating internal voids and cracks that are large compared with the intrinsic pore size. As a result, overlapping sharp bulk-like Cp features and rounded features due to 8S5 in residual aerogel pores were observed, and no quantitative separation of these features could be achieved. 3

ISSN:0267-8292    

DOI:10.1080/026782997209405

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

2-Deoxyguanosine 3 5-cyclic monophosphate forms in water cholesteric and hexagonal columnar mesophases. The polymorphic behaviour and the structural building blocks of the liquid crystalline phases, as determined by optical microscopy, CD spectroscopy and X-ray diffraction, are comparable to those found with all the deoxyguanylates investigated so far (in particular with deoxuguanosine 5- and 3-monophosphate). The present results show that the formation of a stacked array of planar G-tetramers, a necessary condition for the existence of the columnar mesophases, occurs even in the absence of hydrogen bonding groups linking the molecules along the length of the columns.

ISSN:0267-8292    

DOI:10.1080/026782997209414

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Details of the transitional properties of four homologous series of U-shaped liquid crystal materials, the benzene-1,2-di-(4-carboxyalkoxybenzylidene-4-n-alkylanilines), are presented. The spacers incorporate 3 to 6 methylene units, whilst terminal aliphatic chain lengths are varied from 1 to 12 units. Members of the two homologous series with an odd number of methylene units in the spacer form nematic and smectic phases as a function of terminal chain length. Materials with an even number of methylene units in the spacer are purely smectogenic, and in both series the first two homologues form only smectic B phases. For all four series the higher homologues show the phase sequence SF/I-SC-SA-I. X-ray diffraction studies have shown that these smectic phases are composed of molecules arranged in bilayers.

ISSN:0267-8292    

DOI:10.1080/026782997209423

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

As a self-organizing macromolecule, hydroxypropylcellulose serves as an excellent candidate for studies of complex polymer mixtures. In this work, we examine aqueous mixtures composed of two hydroxypropylcellulose grades, Klucel-F (HPC) and Klucel-H (HHPC), with molecular weights of 10 5 and 10 6 g mol - 1, respectively. Polarized light microscopy and deuterium nuclear magnetic resonance have been utilized to ascertain changes in the chiral nematic mesophase of HPC upon addition of 15 wt% HHPC. Results obtained here suggest that the HHPC either disrupts the molecular organization of the HPC mesophase, or induces immiscibility and partitions between HPC- and HHPC-rich phases.

ISSN:0267-8292    

DOI:10.1080/026782997209432

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this article we describe the self-assembling properties of alkyl substituted xylitols in relation to both thermotropic and lyotropic liquid crystalline mesophases. Three series of substituted xylitols were prepared where aliphatic chains of varying length were attached to a xylitol moiety via ether, thioether and ester linking groups. The thermotropic properties were investigated by thermal polarized light microscopy and differential scanning calorimetry, and evaluated as a function of chain length and linking group. The lyotropic phase behaviour was investigated via the addition of water to each material at room temperature. The efficiency for forming thermotropic phases was found to be reversed for the lyotropic phases in respect of the three series, i.e. as a function of the linking unit.

ISSN:0267-8292    

DOI:10.1080/026782997209441

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor