摘要:

A numerical technique has been developed to model texture in nematic liquid crystals. The technique differentiates between splay, twist and bend distortions and includes splay-splay compensation. The technique is tested by the simulation of the Freedericksz transition and by the determination of minimum energy director fields for specific boundary conditions. To model the bulk, periodic boundary conditions are imposed. The effect of elastic anisotropy on disclination character has been investigated by terminating simulations before all the defects have been annihilated. With a low twist constant, twist disclinations are observed; with a high twist constant, wedge disclinations are observed. With a low twist constant and high splay constant, realistic for polymeric liquid crystals, features observed experimentally are simulated.

ISSN:0267-8292    

DOI:10.1080/026782997208415

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The anchoring of nematic liquid crystals on self-assembled monolayers (SAMs) formed by the chemisorption of semifluorinated thiols or alkanethiols on gold is compared and contrasted. The planar anchoring of 4-n-pentyl-4-cyanobiphenyl (5CB) observed in the past on SAMs formed from alkanethiols is also observed on SAMs formed from semifluorinated thiols. The azimuthal anchoring of 5CB, however, differs on these two types of surfaces: nematic 5CB anchored on SAMs formed from alkanethiols has a grainy appearance due to the formation of domains with sizes 10 mum whereas 5CB forms large domains (100 mum) with diffuse branches emerging from defects of strength 1/2 when anchored on SAMs formed from semifluorinated thiols. Mixed (two-component) SAMs formed from either short and long semifluorinated thiols or short and long alkanethiols cause homeotropic anchoring of 5CB. We discuss these results in light of the known differences in the structure of SAMs formed from alkanethiols and semifluorinated thiols, i.e. the tilt of the chains and conformational freedom (flexibility) of the chains within these SAMs.

ISSN:0267-8292    

DOI:10.1080/026782997208424

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The phase diagrams for enantiomers and their racemic counterparts have been compared in order to determine the influence of chirality on re-entrant phenomena. It has been found that chirality affects the location of the partially bilayer SmAd and monolayer smectic SmA1 phase areas, while the position of the smectic X phase remains nearly unchanged. This result shows that the N-SmA phase transition is influenced by a molecular chiral discrimination effect. Moreover, in enantiomeric systems, a N* re1-N* re2 phase transition has been detected by DSC within the re-entrant nematic gap which is limited by the smectic Ad and the SmX phases. Based on preliminary data, the SmX phase seems to be either a weakly tilted SmC antiphase or an incommensurate orthogonal mesophase.

ISSN:0267-8292    

DOI:10.1080/026782997208433

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this paper the director configurations and the free energies of a nematic droplet with a surface normal anchoring condition are calculated numerically. For this surface anchoring, a transition occurs between the radial and axial structures with respect to an applied field. In the calculation of the director configurations, the position of a disclination has been fixed. Comparing the free energies for different disclinations, the stable position which gives the minimum free energy is found. In calculating the free energy of a droplet, it is assumed that the free energy density of the nematic phase does not exceed the isotropic free energy density, so that the large distortion in the vicinity of the disclination causes a nematic-isotropic transition and the free energy density of the disclination core becomes equal to the isotropic free energy density. The director configuration in a droplet is calculated as a function of an applied field for different isotropic free energy densities, elastic constant ratios and droplet shapes. The relation between the radial-axial structure transition and these factors are clarified.

ISSN:0267-8292    

DOI:10.1080/026782997208442

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We present the results of molecular dynamics simulations of the Gay-Berne model of liquid crystals, supercooled from the nematic phase at constant pressure. We find a glass transition to a metastable phase with nematic order and frozen translational and orientational degrees of freedom. For fast quench rates the local structure is nematic-like, while for slower quench rates smectic order is present as well.

ISSN:0267-8292    

DOI:10.1080/026782997208451

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We consider a smectic A* phase in a capillary with surface anchoring that favours parallel alignment. If the bulk phase of the smectic is the standard twist-grain-boundary phase of chiral smectics, then there will be a critical radius below which the smectic will not have any topological defects. Above this radius a single screw dislocation in the centre of the capillary will be favoured. Along with surface anchoring, a magnetic field will also suppress the formation of a screw dislocation. In this note, we calculate the critical field at which a defect is energetically preferred as a function of the surface anchoring strength and the capillary radius. Experiments at a few different radii could thus determine the anchoring strength.

ISSN:0267-8292    

DOI:10.1080/026782997208460

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The solubility of known azo dyes was in the order of dye skeleton: trisazo and aryloxycarbonyl disazo dyes < aryloxy disazo dyes < disazo dyes. The perfluoroalkyl derivatives were synthesized and found to be more soluble than the corresponding alkyl analogues except for a series of aryloxycarbonyl disazo dyes. Dichroism (order parameter,S)was in the order of dye skeleton: disazo dyes < aryloxycarbonyl and aroyloxy disazo dyes < trisazo dyes. No marked difference in the dichroism among perfluorobutyl, hexyl and octyl derivatives was observed. All the ester-type disazo dyes showed good S values (> 0.76).

ISSN:0267-8292    

DOI:10.1080/026782997208479

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We calculate the liquid crystal phase diagram for a model fluid with Gay-Berne interparticle potential using the Tarazona smoothed-density approximation of density functional theory. Vapour, liquid, nematic and smectic A phases are considered. For length to breadth ratio kappa 3 and energy anisotropy kappa 5, comparison with the simulation data of de Miguel et al. shows reasonable agreement.

ISSN:0267-8292    

DOI:10.1080/026782997208488

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A structural characterization of two series of ferroelectric low molar mass organosiloxanes is described. X-ray and dilatometry studies have been used to determine the impact of variations in mono- or di-mesogen architecture, halogen substitution and siloxane content on the mesophase structure and thermal behaviour. All of the compounds exhibit smectic C* mesophases with high tilt angles. Bromo substituted compounds are consistently found to exhibit higher tilt angles than their fluoro analogues, and a strong odd-even effect in melting temperature is observed for the dimesogenic bromo series.

ISSN:0267-8292    

DOI:10.1080/026782997208497

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The irreversible electro-optical response (memory effect) of 'liquid crystal-aerosil' suspensions under the influence of an electric field is investigated. Thereby, the influence of the aerosil concentration on the efficiency of the memory effect is studied. The experimental results are discussed in the frame of a model where the filled nematic is considered as a system of aerosil agglomerates in a liquid crystal matrix stabilized by the forces of liquid crystal orientational elasticity.

ISSN:0267-8292    

DOI:10.1080/026782997208505

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor