摘要:

On the basis of the worked out modification of the continuum theory of ferronematics the Fredericksz transitions and orientational birefringence induced by magnetic and/or electric field are studied. A comparison with the available experimental data is made.

ISSN:1058-725X    

DOI:10.1080/10587259508034553

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The characterization of Langmuir–Blodgett (LB) orientation films in terms of the optical retardation as a function of the LB depositing velocity has been studied, and the surface anchoring strength of the LB films for a nematic liquid crystal has been estimated. The optical retardation decreases as the LB depositing velocity increases. In contrast, the anchoring strength increases as the LB depositing velocity increases. The macroscopic anchoring strength may not have a positive correlation with the optical retardation which reflects the microscopic orientational order. Furthermore, we succeeded in generating the high pretilt angle by only using the LB method. The pretilt angle gradually decreases with increasing the depositing velocity.

ISSN:1058-725X    

DOI:10.1080/10587259508034554

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The change of dynamic viscoelastic properties of liquid crystals was monitored using the quartz crystal resonator by measuring the resonant frequency and the resonant resistance of the quartz crystal during impression of voltage pulses. The viscoelastic change showed different responses as the effects of the applied voltage amplitude, an alignment film and the anisotropy of dielectricity. The higher applied voltage and a cell with alignment films gave larger responses than lower applied voltage and a cell without alignment film, respectively, and the positive and negative anisotropy of dielectricity gave opposite responses. The diagramed resonant frequency and resonant resistance for the voltage pulses showed hysterisis, and these changes are understood as the hysterisis of the dynamic orientation processes of liquid crystal molecules.

ISSN:1058-725X    

DOI:10.1080/10587259508034555

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Anisotropic sphericalcellsdispersed in an isotropic medium were observed, using polarizing microscopy, in asymmetric cellulose acetate (CA) membranes. Membranes CA-400 and CA-316 were prepared from ternary casting solutions of CA-acetone-formamide and CA-acetone-magnesium perchlorate/water respectively. The content of nonsolvent, formamide, was varied to yield membranes CA-400-22, CA-400-27 and CA-400-32 that show a decreasing number of larger anisotropiccellswith the increase of nonsolvent content. The membranes CA-316 were subjected to a heat treatment—annealing—at varying temperatures yielding membranes CA-316-50, CA-316-68 and CA-316-86. The crystallinity observed was dependent on the temperature of this heat post-treatment. The selective permeation properties are correlated with the ratio of isotropic to anisotropic phases at the membrane skin surface. This ratio is in turn dependent on the casting solution composition-type and concentration of nonsolvent and on the annealing treatment. The results were interpreted considering that a lyotropic mesophase develops during the evaporation of the solvent after spreading the solution for film preparation. The ternary system is initially isotropic but as the polymer concentration (C) increases due to solvent evaporation, anisotropic droplets may appear at some value ofC≈C*, where C* is the critical concentration for the isotropic to liquid crystal phase transition in the CA/acetone (binary) system.

ISSN:1058-725X    

DOI:10.1080/10587259508034556

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A variety of side chain liquid crystalline ionic polysiloxanes with quaternized ammonium groups incorporated into the mesogenic moiety or into the spacer have been synthesized and studied by a combination of DSC, TGA, polarizing microscopy and X-ray diffraction. The polysiloxanes exhibit a nematic mesophase. Due to their flexible main chain, the transition temperatures are low. Thermal stability and liquid crystallinity of quaternized and unquaternized polysiloxanes are compared. It appears that in these ionic polymers the geometry of the mesogenic group plays an important part in the development of the mesophase.

ISSN:1058-725X    

DOI:10.1080/10587259508034557

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The crystal and molecular structure of 4′-cyanophenyl-4-n-butoxybenzoate, which exhibits a monotropic nematic phase, has been determined using single crystal X-ray diffraction data. The crystals belong to the orthorhombic system, Pccn, a = 35.872(8) Å, b = 11.331 (3) Å, c = 7.773 (2) Å, Z = 8. The structure has been solved by direct methods and refined to an R-value of 0.0502 with Fo> 2σ (Fo). The molecular structure shows that the butoxy group is extended in the gauche-conformation. The long molecular axes are arranged parallel to [100] and lie in y ≈ 0.11, 0.39, 0.61 and 0.89. In addition to that, the molecules are arranged in layers which are perpendicular to the a-axis have a thickness of a/2 (≈ 18 Å). Cyano-cyano contacts, N… N′ ≈ 3.54 Å, are found.

ISSN:1058-725X    

DOI:10.1080/10587259508034558

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Guest-host type mixtures of a liquid crystal and dichroic dyes are theoretically analyzed by means of the Flory–Ronca lattice theory.

ISSN:1058-725X    

DOI:10.1080/10587259508034559

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A homogeneous alignment of liquid crystal mixtures, E7, was produced by phthalocyanine (Pc)-derived Langmuir-Blodgett (LB) films. The Pc LB film was studied by scanning tunneling microscopy. Experimental results suggest that the molecular aggregates and molecular grooves between these aggregates may both be responsible for the alignment.

ISSN:1058-725X    

DOI:10.1080/10587259508034560

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Crystal and molecular structure of a mesogenic compound N,N′-Bis-p-(Butoxybenzylidene)-α,α′-bi-p-Toluidine has been determined by direct methods. The compound crystallizes in triclinic system with space group P1. Cell parameters area= 6.116(3),b= 7.916(3),c= 31.421 (8)Å, α = 92.39(2),β= 92.35(3),y= 96.59(2)° andz= 2. The two symmetrical fractions of the molecule are almost planar but the angle between these planes is 63.5°. The molecules are arranged in tilted layers which is precursor to the tilted smectic phase. Crystal-mesophase transition is discussed.

ISSN:1058-725X    

DOI:10.1080/10587259508034561

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Fifty-six compounds containing cyclopropyl, cycloheptyl, or cyclooctyl ring systems, members of six homologous series of azomethines related to the nO.m series, have been prepared and their liquid crystal behavior investigated. These series show less extensive smectic polymorphism than the analogous cyclopentyl and cyclohexyl derivatives, previously reported. The effect on nematic thermal stability of an increase in the size of the cycloalkyl group present in related azomethines is discussed. Azomethines containing cyclopropyl, cycloheptyl and cyclooctyl rings have lower nematic thermal stability than their cyclopentyl and cyclohexyl homologues.

ISSN:1058-725X    

DOI:10.1080/10587259508034562

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor