摘要:

The factors which govern the stability of lyotropic amphiphilic nematic phases are delineated and then used to design mesogens which give rise to stable NCand NDphases on dissolution in water. The synthesis and phase behaviour of novel discoid amphiphiles, designed to form NCphases, are described.

ISSN:0267-8292    

DOI:10.1080/02678298608086498

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We present the results of Q.N.S. studies for two members of the homologous series of alkoxyazoxybenzenes, CnH2n+1O-ϕ-N2O-ϕ-OCnH2n+1; PAP (n= 2) and POAB (n= 3). The Q.N.S. measurements were performed on the non-deuteriated (d0-PAP andd0-POAB) and the chain deuteriated samples,d10-PAP andd14-POAB. Three models were fitted to the experimental data: (1) uniaxial rotational diffusion of the molecule around the axis with the smallest moment of inertia, (2) uniaxial rotational diffusion of the two moieties of the molecule around the N-ϕ bonds, (3) 180° instantaneous jumps of the two moieties of the molecule around N-ϕ bonds. We have assumed the molecule to exist in the trans conformation. The translational diffusion of the molecules and the methyl groups' reorientation were neglected. It turned out that model (3) does not describe the experimental data well. Models (1) and (2) describe the experimental data equally well, giving no preference for the axis of rotation. However, comparison of our results with those obtained from dielectric relaxation suggests the choice of model (2) as responsible for the Q.N.S. data. The correlation times determined by fitting to both rotational diffusion models are of the order of several picoseconds. However, the correlation times determined ford10-PAP andd14-POAB are two or three times longer than ford0-PAP andd0-POAB, respectively, which indicates the existence of additional motion of the end chains.

ISSN:0267-8292    

DOI:10.1080/02678298608086499

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We have simulated the behaviour of a model, binary mixture of nematogens composed of cylindrically symmetric particles using the Monte Carlo technique. The characteristics of the model mixture were chosen to be in accord with most of the assumptions made in the Humphries–James–Luckhurst theory of liquid crystalline mixtures. The results of the simulation experiments allow us to test, for the first time, the validity of the molecular field approximation in this theory. In addition to the second rank long range orientational order parameters for both components of the mixture we have also determined certain orientational pair correlation functions. These enable us to investigate the ability of one component to enhance the order of the other component or the same component in its vicinity.

ISSN:0267-8292    

DOI:10.1080/02678298608086500

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The transient behaviour of the director of a nematic mesophase subjected to spinning at frequency Ω in an applied magnetic fieldH0is investigated by E.S.R. All experiments were conducted with Ω > Ωc, Ωc= (ΔH20/2λ1). Here Δχ is the anisotropic magnetic susceptibility and λ1is the rotational twist viscosity of the nematic. The theory of Leslie, Luckhurst and Smith is used to analyse Fourier transformed time domain data and their result for the dependence of ω, the director rotation rate, on Ω (ω = (Ω2− Ω2)1/2) is confirmed for a range of values ofH0and Ω. Values of Ωcfor Phase IV, Phase V and the alkylcyanobiphenyls K15, K18 and K21 are reported. Linewidths in the frequency domain are shown to depend on the twist viscosity of the mesophase and possible evidence for micro-domains in Phase IV and Phase V is presented. The values of Ωcreported for Phase IV differ by a constant from the values calculated using literature values of Ω1and Δχ.

ISSN:0267-8292    

DOI:10.1080/02678298608086501

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The dispersion curves and attenuation factors of the Bloch eigenwaves in heiicoidal liquid crystals (chiral smectic C and cholesterics) are calculated using the 4 × 4 characteristic matrix method. Four possible types of eigenmodes are seen to exist in the medium. The reflection peaks, which correspond to odd parts of the full pitch, are total reflection peaks, while those corresponding to even parts of the full pitch are composed of three branches at high incidence angles, where the outer branches are selective reflection and the central one is a total reflection peak. Selective reflection regions occur only at the edges of the Brillouin zones, while total reflections can occur anywhere inside the zones. The former are interpreted according to the coupled mode theory as resonant Bragg reflections, with the latter as exchange Bragg reflections. When the tilt direction exceeds the propagation direction, the central branch of the even sequence of peaks starts to be due to resonant Bragg reflections. The first order peak for cholesterics becomes strongly structured at large incidence angles.

ISSN:0267-8292    

DOI:10.1080/02678298608086502

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Results are reported of light scattering and dielectric measurements on solutions of 4-n-pentyl-4′-cyanobiphenyl (5CB) and 4-n-pentyl-4′-cyanobicyclo-hexane (5CCH). Correlation factorsg1andg2are deduced from the measurements, and are discussed in terms of a model for molecular association. It is concluded that at low concentrations the association between 5CB molecules is substantially greater than that between 5CCH molecules.

ISSN:0267-8292    

DOI:10.1080/02678298608086503

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The thermotropic phase transitions and the mesophase structure of two long-chain alkyl pyridinium halides are described. From small angle X-ray diffraction, optical microscopy, differential scanning calorimetry and dilatometry, the single liquid-crystalline phase found in each material is identified as smectic A. It is argued that the molecules within a layer are oriented alternately and packed in an interdigitated fashion, with the anions sandwiched between the pyridinium rings.

ISSN:0267-8292    

DOI:10.1080/02678298608086504

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

L'effet de la rotation rapide dans le champ R.M.N, des mélanges de cristaux liquides nématiques d'anisotropie diamagnétique opposée est étudié. Le comportement de ces mélanges est totalement différent de celui des cristaux liquides nématiques purs. En effet quand l'anisotropie macroscopique, Δχ, devient faible le comportement du directeur n'est plus gouverné par le couple magnétique, mais par les propriétés inertielles du milieu de telle façon qu'à des vitesses de rotation élevées le directeur du cristal liquide se trouve distribué dans le plan perpendiculaire à l'axe de rotation quelque soit la valeur de Tangle entre le champ magnétique et l'axe de rotation. Ce comportement a été étudié en suivant l'évolution du couplage F–F de CF2Cl‒CCl3dissout dans le mélange et aussi en suivant l'évolution des déplacements chimiques anisotropes13C d'une des composantes du cristal liquide luiměme.

ISSN:0267-8292    

DOI:10.1080/02678298608086505

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The structure of the core region of a screw dislocation in smectic A liquid crystals is investigated by a Ginzburg–Landau type expansion of the smectic order parameter. The core radius and the energy of a screw dislocation are discussed.

ISSN:0267-8292    

DOI:10.1080/02678298608086506

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We have studied the behaviour of the density, ϱ, as a function of temperature for a number of side-chain liquid-crystalline polymers. The polymers have a polysiloxane backbone and a benzoate ester side group with different tails or flexible spacers. From the values of ϱ in the smectic A phase and from the layer thickness obtained from X-ray experiments we have determined a molecular area in the plane of the layers. The evolution of this parameter shows clearly the asymmetrical role of the tail and the spacer.

ISSN:0267-8292    

DOI:10.1080/02678298608086507

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor