摘要:

Lateral substitution of mesogenic systems is shown to produce a great diversity of new liquid crystalline structures. The effect of such structural changes on the physico-chemical and electro-optical properties of laterally substituted nematic systems is discussed and compared with that of their unsubstituted analogues.

ISSN:0267-8292    

DOI:10.1080/026782997207704

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

4-Hexadecyloxyphenyl-4-substituted benzoates, Ia-d, and 4-substituted phenyl-4- hexadecyloxy benzoates, IIa-d, with the substituents CH3O, Cl, CN, and NO2, respectively, were prepared and characterized by infrared spectroscopy and the apparent solution dipole moment measured using cyclohexane as a solvent. Smectic A mesophase stability was investigated by differential scanning calorimetry and polarized light microscopy. The effects of structural changes on phase transitions in these two series of compounds are discussed in terms of dipole and mesomeric effects.

ISSN:0267-8292    

DOI:10.1080/026782997207713

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This work relates to the control of switching in ferroelectric liquid crystal devices. By considering the various parameters which influence the switching process a method of engineering both the location and threshold of domain nucleation sites has been developed. We have found that deliberate modification of the surface morphology has a profound influence on the domain switching process. This paper discusses the experimental cell construction and switching results.

ISSN:0267-8292    

DOI:10.1080/026782997207722

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The phase diagram of equilibrium configurations in thin hybrid nematic cells has been investigated in the framework of Landau-de Gennes theory extended to include weak surface anchoring. Surface interactions linear in the tensor order parameter were assumed and biaxiality was induced by the surfaces. It was found that in addition to the usual configuration where the director bends continuously from one plate to the other, there is also a possible configuration where bend does not occur, but where there is an eigenvalue exchange; i.e. the eigenvector of the tensor order parameter associated with the eigenvalue of the largest magnitude is different in different regions of the cell. Furthermore, for very small cell thickness a third possibility occurs: the eigenvector corresponding to the eigenvalue with the largest magnitude is uniform throughout the cell; it is either parallel or perpendicular to both plates depending upon the dominant surface interaction. Continuous transitions occur between the different configurations.

ISSN:0267-8292    

DOI:10.1080/026782997207731

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this short article, we draw attention to the pioneering studies of Daniel Vorlander, who lived from 1867 to 1941 and worked in Halle, Germany between 1890 and 1935. The number and range of compounds synthesized under his guidance are truly vast, but much of his work is hidden away in Doctoral theses. All of these data are collected in the LiqCryst [1] database and, therefore, now having access to the results of his life's work, we outline some of his achievements and pay tribute to his remarkable contribution to liquid crystal research.

ISSN:0267-8292    

DOI:10.1080/026782997207740

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Fluorine-containing negative dichroic 1,4-bis(acylamino)anthraquinone dyes have been synthesized. The solubility of the dyes based on the acyl moieties in chloroform was in the order of hexanoyl>4-butylbenzoyl>3,5,6-trichloro-octafluorohexanoyl>perfluoroalkanoyl, 4-(perfluorobutyl)benzoyl, pentafluorobenzoyl, and benzoyl. The negative dichroism of the dyes was greater as the l / d ratio increased and the theta value was closer to 90. Only some 3,5,6-trichloro-octafluorohexanoyl derivatives were sufficiently soluble. Their S values were -0.26 to -0.29 in ZLI-4792.

ISSN:0267-8292    

DOI:10.1080/026782997207759

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We have attempted to investigate the dependence of the elastic behaviour of liquid crystal dimers on the parity of the spacer linking the two mesogenic groups by using an indirect method. In this the nematic phase formed by the dimers is converted to a chiral nematic by the addition of a chiral dopant. The uniform distribution of the director in the helical structure of the mesosphase is perturbed by the magnetic field of an ESR spectrometer. The extent of the field-induced perturbation is then determined from the appearance of the ESR spectrum of a nitroxide spin probe dissolved in the mesophase. The observed difference in the extent of the field-induced perturbation is analysed in terms of the higher orientational order of the even with respect to the odd dimer. However, the theoretical model fails to account for this difference in behaviour and a possible explanation is discussed.

ISSN:0267-8292    

DOI:10.1080/026782997207768

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A theoretical study of light transmission, linear dichroism and birefringence of partially ordered dispersions of bipolar nematic droplets in a polymer matrix is presented. The treatment rests on the single scattering approach to an ensemble of uncorrelated and noninteracting anisotropic particles. Theoretical evaluations of the extinction cross sections and phase functions are performed in the anomalous diffraction approximation. Four basic model systems are analysed: PDLC and NCAP films in an external electric field, and PDLC and NCAP films under uniaxial mechanical deformation. The calculated dependences of the generalized parameters characterizing the light transmission, dichroism and birefringence on the angle of incidence of the probing light, droplet size and shape, refractive indices of the LC and polymer, and parameters of the external field are presented graphically and discussed in detail.

ISSN:0267-8292    

DOI:10.1080/026782997207777

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Polymer dispersed liquid crystals (PDLCs) are materials composed of liquid crystal microdroplets dispersed in a polymer matrix. Their electro-optic properties make them useful for applications as large-area electrically switchable architectural windows (smart windows). For these applications, the key parameters of performance are the haze (both normal and offaxis) and the opacity. In the present work we show how it is possible to prepare a high performance smart window by controlling the haze and opacity of PDLC films using the polymer induced phase separation (PIPS) method.

ISSN:0267-8292    

DOI:10.1080/026782997207786

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The aggregate structure of the discotic compound 2,3,6,7,10,11-hexakispentyloxytriphenylene (HPT) was studied both for the crystalline state and the liquid crystalline state by using electron crystallography and a molecular simulation approach. In the crystalline state, HPT was found to adopt an orthorhombic P22 1 2 space group with cell parameters a = 36.73 A, b = 27.99 A and c = 4.91 A. Molecular packi1ng calculations were conducted to elucidate the molecular conformation and mutual orientational characteristics in the different states. Phase transitions and relationships are discussed from a structural point of view.

ISSN:0267-8292    

DOI:10.1080/026782997207795

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor