摘要:

In finite samples of ferroelectric liquid crystals with parallel smectic layers inclined with respect to the sample surfaces, the chevron structure usually occurs. For the same surface anchoring conditions, the twisted molecular organization may also appear, but in contrast with the bookshelf layer geometry, the twist is confined either to the upper part of the chevron, with the lower part untwisted or vice versa. Therefore two different director configurations with respect to the chevron interface can be recognized. These different configurations can coexist and they can be mediated by the so called inversion line. In this communication, we describe this inversion line within the simplest approximation of the chiral smectic C* elasticity. The self-energy of the inversion line, together with its core energy estimated on the basis of the Peierls-Nabarro model, gives the energetically more favourable solution from two that are possible. Finally the interaction of the inversion line with 2/pi-twist disinclination (unwinding line) is discussed and used to explain the observed coalescence of parts of these lines in the terms of their mutual interaction.

ISSN:0267-8292    

DOI:10.1080/02678299508036715

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

New antiferroelectric liquid crystals (AFLCs) with a trifluoromethyl group at the chiral centre were synthesized using optically active 3-(4-methoxyphenyl)-4,4,4-trifluorobutanoic acid. The new AFLCs showed the phase sequence on cooling: isotropic liquid (I)-smectic A (Sa) phase-antiferroelectric (AF) phase-crystal (Cr). In the antiferroelectric phase, a d.c.-threshold, a double hysteresis loop, a small dielectric constant value and two sharp switching-current peaks were observed. These are the first examples that are AFLCs which do not have a carbonyl moiety in the molecule.

ISSN:0267-8292    

DOI:10.1080/02678299508036716

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The non-linear interaction of arbitrary polarized light with smectic layer deformations in smectic A liquids (SA) is considered. It is shown that the combined effect of anisotropy, fluidity and a characteristic kind of deformation cause a number of specific non-linear optical phenomena. Two-wave mixing in SAtransforms into a partly degenerate four-wave mixing (FWM) when the polarization and the direction of propagation of the coupled electromagnetic (EM) waves are arbitrary. The interference of the EM waves gives rise to a dynamic grating of layer deformations without a change of mass density of SA. In the resonant case a propagating mode of a second sound (SS) is excited. The non-linear phenomena are analysed by solving the self-consistent system of the Maxwell equations for the non-linear anisotropic inhomogeneous medium and the hydrodynamic equations of SAin the external EM field. The explicit expressions of the EM and SS waves amplitudes are obtained. It is shown that the coupled fundamental EM waves undergo the parametric amplification and the phase cross-modulation, and their amplitudes as well as the SS wave amplitude are spatially localized. The energy transfer between the coupled EM waves is non-reciprocal. The scattering of the fundamental EM waves by the dynamic grating results in the appearance of additional harmonics with combination frequencies and wavevectors. The light induced dynamic grating also generates a longitudinal electric field due to the flexoelectric effect.

ISSN:0267-8292    

DOI:10.1080/02678299508036717

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The synthesis and liquid crystal properties of eight members of the homologous series of 1-(4′-n-alkoxy-2,2′,3,3′,5,5′,6,6′-octafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)-ethanes and eight members of the corresponding -ethanes, which have the E-configuration, are reported. These compounds are nematic, the ethenes having a considerably mesophase higher thermal stability than the analogous ethanes.

ISSN:0267-8292    

DOI:10.1080/02678299508036718

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Four new chiral series with benzoate cores have been synthesized and characterized. The mesomorphic properties have been analysed by optical microscopy on the pure enantiomeric and the racemic compounds and on mixtures, by D.S.C. and by electro-optic measurements. Three of the series (hydrogenous, monofluoro-substitutedorthoto the alkoxy chain, and difluoro-substituted) display a very rich polymorphism including SA, S*α, S*C, S*FIand S*CAphases, whereas the series monofluoro-substituted in themeta-position does not exhibit S*FIand S*CAphases any more except for the dodecyloxy derivative, but gives a large enantiotropic S*Cα, phase. A comparison of these four series leads to a discussion about the effect of the transverse dipole moment on the existence of the S*CAphase.

ISSN:0267-8292    

DOI:10.1080/02678299508036719

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper investigates the effect of weak anchoring on static orientation patterns in a sample of nematic liquid crystal confined to a cylindrical annular geometry, in the presence of a magnetic field. The particular arrangement considered in detail is that in which a magnetic field is applied in the azimuthal direction to a sample of liquid crystal that is initially uniformly aligned parallel to the cylindrical axis and is weakly anchored at the inner cylinder, but strongly anchored at the outer cylinder. A static solution of the non-linear continuum equations is presented which suggests a possible experiment for evaluating the surface elastic coefficientk24. In addition, a linear stability analysis based on the dynamic theory yields results for critical phenomena in agreement with those derived from the non-linear solution.

ISSN:0267-8292    

DOI:10.1080/02678299508036720

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Liquid crystal (LC) mixtures of a reactive diacrylate and a commercial ferroelectric liquid crystal (FLC) mixture were produced. The mixtures were brought into cells provided with orientation layers in which various orientations such as uniaxial and twisted orientations, could be induced. When the desired orientation had been obtained, the polymerization of the reactive molecules was induced creating a three-dimensional anisotropic network containing the FLC molecules which were not chemically attached to the network (ferroelectric gels). The presence of the anisotropic network was found to have a large effect on various properties of the FLC molecules. For example, complex orientations (for example, 180° twisted) obtained by polymerization (formation of the gel) in the nematic phase remained unchanged when the gel was cooled to the FLC phase. Likewise uniaxial orientation, which cannot be realised in thick cells containing the pure FLC, could be realised when ferroelectric gels were used. For this reason the ferroelectric gels will be referred to as ananisotropic network-stabilized FLC.Optical properties such as effective birefringence and tilt angle were also influenced by the network. When use was made of a network with a lower birefringence than the FLC, a reduced effective birefringence in gels was observed. This is important for technologies involving thicker cells. The switching covered a range of voltages in the case of the gels, instead of showing a well-defined threshold voltage as in the bulk. The possibility of using this effect to obtain grey scales in cells during passive addressing has also been demonstrated.

ISSN:0267-8292    

DOI:10.1080/02678299508036721

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The preparation of 4′-alkyl- and 4′-alkoxy-4-cyano-3-fluorobiphenyls by four different procedures is described and discussed; the best method involves palladium(0)-catalysed coupling of arylboronic acids and 4-bromo-(or 4-iodo-)-2-fluorobenzonitrile. The effects on transition temperatures of fluoro substitutionorthoto the terminal cyano group in biphenyls are compared with the effects in other terminal cyano compounds and in mesogens without a terminal cyano group. The effect of theorthofluoro substituent in 4-cyanobiphenyls is particularly large and is probably due to the severe disruption of antiparallel correlations; the depressions of the smectic A and nematic phase stabilities are similar which suggests that, as for compounds with alkyl or alkoxy terminal groups, the fluoro substituent at the 3-position has a tendency to enhance smectic character, but this is offset by the molecular broadening it causes.

ISSN:0267-8292    

DOI:10.1080/02678299508036722

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The hexatic smectic B (Hex B) phase is commonly encountered among hydrogen-bonded liquid crystal materials. Among enaminoketone and Schiff's base compounds, twenty homologous series(c.102compounds) exhibiting orthogonal mono-or bi-layer hexatic phases were identified by combined microscopy and DSC. Phase transitions from crystal B (CrB) of Sfto Hex B as well as from Hex B to Sf, Saor Scphases were observed within the range 50 to 190°C. Temperature ranges of the Hex B phase detectable by DSC varied from 0.2 to 20°C. Within two groups of three-ring enaminoketones, the formation of the Hex B phase was found to be controlled by both inductive and mesomeric components of the Hammett constants of the terminal substituents of the molecules.

ISSN:0267-8292    

DOI:10.1080/02678299508036723

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The laser intensity modulation method (LIMM) was applied to the investigation of polarization distributions in sandwich cells of a side chain liquid crystalline polymer (LCP). The thermal poling procedure using a pulsating electric field was carried out for the nematic phase at 80°C. After cooling down the samples to room temperatureTR(i.e. below the glass transition temperature,Tg) a rather perfect alignment of the side chains could be obtained. Our first LIMM investigations atTRshow a nearly homogeneous polarization profile in the LCP layer.

ISSN:0267-8292    

DOI:10.1080/02678299508036724

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor