摘要:

The structures of tetra-n-butylammonium bromide,N(C4H9)4Br (abbreviated: 4Br) and tetra-n-butylam-monium iodide, N(C4H9)4I (abbreviated:4I) have been determined. For 4Br:Mw= 322.4 Da,c-centered monoclinic space group C2/c,a= 14.409(5) Å,b= 13.901(2)Å,c= 20.345(9)Å, β= 110.18(3)Å,V=3729.4Å3,Z=8,Dc= 1.148 g/cm3,F(000)= 1392,R=0.098 for 1311 reflections. For 41:Mw= 369.4 Da, c-centered monoclinic space group C2, α = 14.482(4)Å,b= 14.318(4)Å,c= 19.975(7)Å, β = 110.86(2)°,V=3870Å3, Z = 8,Dc= 1.230 g/cm3,F(000) = 1536,R= 0.142 for 1899 reflections. The structure analysis shows that the n-butyl chains are distorted to different degrees from their all-transconformations and are connected through the quaternary nitrogen with one or twogauche- bonds. The plastic crystalline mesophase for 41 seems to be possible because of a lower packing fraction that produces larger deviations of the bond-rotation angles from the intramolecular energy-minimum, not found for 4Br. The condis crystal mesophase for4Br, in turn, may be due to a more intermeshing cation structure, possible because of the higher packing fraction with the Br−anion. Higher homologues of the tetra-n-alkylammonium salts form only condis-crystal mesophases, lower homologues, only plastic-crystal mesophases. The low-temperature crystal structures of all salts of this homologous series contain similar cation conformations. Then-butyl and longer alkyl chains form layer-like crystals with methyl surfaces. The somewhat poor fit of computed and experimental structures does not arise from experimental error, but is due to static packing disorder.

ISSN:1058-725X    

DOI:10.1080/10587259508037306

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper reports results of a detailed examination of the low frequency dielectric properties of dilute anisotropic solutions of two polar mesopens, 4-cyano-3-fluorophenyl-4′-propylbenzoate(C3FCN) and 4-cyanophenyl-4′-butylbenzoate(C4CN), as solutes in a non-polar liquid crystal solvent. At low concentrations the effects of dielectric weening are minimised. and the association of mesogens due to dipole-dipole forces can be studied. The measurements suggest that at very low concentrations the dipole-dipole interactions result in a small increase in the effective dipole moment. while at higher concentrations local antiferroelectric order becomes dominant. The results are fitted to an association model, which was originally developed to describe the dielectric behaviour of isotropic solutions of polar solutes (alcohols) in carbon tetrachloride solutions.

ISSN:1058-725X    

DOI:10.1080/10587259508037307

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

4,4′-Bis[4-(4-alkoxybenzoyloxy)benzylideneamino diphenyl ether, its 3,4′-analogue, and 1,4-bis[4-[4-(4-alkoxybenzoyloxy)benzylideneamino phenoxy benzene have been found to exhibit mostly an enantiotropic nematic phase. The clearing points of these three homologous series are rather close to each other; for example, the methoxy members give 340,325, and 333°C respectively and the decyloxy members 222,213, and 231°C, suggesting no substantial difference in the molecular shape though the molecules are not quite linear. On the other hand, the mesophase appearing in 4,4′-bis[4-(4-alkoxybenzoyloxy)benzylideneamino diphenylmethanes is of the smectic C type. Thus, the importance of the nature of one-unit linking groups as a factor determining the type of mesophase was demonstrated.

ISSN:1058-725X    

DOI:10.1080/10587259508037308

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A ferroelectric liquid crystal (FLC) cell for flat panel displays with volume stabilized bistable states is described. Volume stabilization is achieved by the FLC/polymer gel dispersion which is prepared by polymerizing a FLC/polymer precursor solution in a suitably aligned FLC display cell. The volume stabilized LC cell gives mechanical stability to FLC displays with internal memory and provides for high contrast shuttering while keeping all other excellent properties of the surface stabilized FLC displays (SSFLCD).

ISSN:1058-725X    

DOI:10.1080/10587259508037309

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A molecular meanfield model for a rectangular columnar to hexagonal columnar phase transition, as observed in case of the HAT series, is presented here assuming the molecules basically to be biaxial objects. The theory is developed for a rectangular lattice having herring-bone packing of the tilted molecules. Various types of phase diagrams for a homologous series are reproduced for different values of molecular biaxiality. Some of them are very similar to the experimentally observed cases but others, particularly involving biaxial nematic phase, are not yet observed. It is shown that a gradual lowering of biaxiality with the addition of flexible chain segments can lead to the full phase sequence observed in the HAT series.

ISSN:1058-725X    

DOI:10.1080/10587259508037310

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The switching mechanism in ferroelectric liquid crystals takes place through domain formation and evolution, and therefore can be considered as a multi-dimensional process with variation in the director orientation over the area ofa switched region as well as with time. It has become commonplace to model the switching using very simple low-dimensional models which do not allow for this. We discuss why these appear to be quite successful, and how the modelling fits in with reality. It is seen that at reasonable switching voltages low-dimensional modelling works well in correctly predicting the time to domain nucleation. At higher voltages this nucleation time dominates and therefore the model is reasonable in this regime.

ISSN:1058-725X    

DOI:10.1080/10587259508037311

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have proposed a statistical-mechanical theory of a nematic liquid crystal composed of ellipsoidal molecules interacting through angle-dependent nonseparable potentials in contact with a solid interacting surface. The theory takes into account pair intermolecular correlations. Within the framework of the theory the concept of an average force potential is used to develop a truncation procedure for arbitrary equation of the chain. The closed system of integral equations for average force potential is similar to that used by Brook-Levinson and Zakharov for uniform nematic phase. These equations are solved numerically and results are given for the cubic closed packing ellipsoidal molecules interacting through Berne–Pechukas potentials. Although the calculations have been made for the nematic liquid crystal, the general approach can be applied to any liquid crystalline phase.

ISSN:1058-725X    

DOI:10.1080/10587259508037312

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Several achiral rigid rod solutes were dissolved in two different cholesteric liquid crystalline solvents, and pitch measurements were made by the Cano wedge, droplet and fingerprint methods. In the first two techniques, no effect of the achiral solutes on the pitch occursat low concentration. Although some regimes of the samples prepared by the fingerprint technique show pitch shortening in the presence of some of the achiral solutes, the overall conclusion is that, contrary to previous reports, there appears to be no convincing evidence for the induction of preferred conformations in achiral solutes.

ISSN:1058-725X    

DOI:10.1080/10587259508037313

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The literature dielectric data of Johari and Goodby on the main relaxation in smectic G phase and on secondary relaxation in the glass of smectic G phase of PBBA has been analyzed to estimate and compare the local and long-range correlation parameters describing the molecular reorientations.

ISSN:1058-725X    

DOI:10.1080/10587259508037314

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

An X-ray study of nitrobenzilidene derivatives ofo-amidoanilines has been carried out. By analysis of the crystallochemical data taking into account an orienting influenceof dipole-dipole interactions a relationship between the molecular and crystal structure of the compounds has been established.

ISSN:1058-725X    

DOI:10.1080/10587259508037315

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor