摘要:

We have developed two types of 4-domain complementary TN (CTN) LCDs: a random type and a position-controlled type. The LC layer in each of the 4-domain CTN-LCDs is divided into four kinds of domain, each of which has directions. The 4-domain CTN-LCDs have wide contrast ratio without light masking layers. In the fabrication, each of their substrates was rubbed in only one direction; no additional step was required, in contrast to the conventional TN-LCD process. We have also fabricated 4-domain CTN TFT panels and confirmed that they have wide viewing angle characteristics without grey scale inversion. a different combination of twist and tilt viewing angle characteristics and high

ISSN:0267-8292    

DOI:10.1080/026782998206263

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The thermotropic liquid crystalline properties of a variety of chiral and racemic dodecyloxy substituted polyols derived from carbohydrates were investigated as a function of the number of hydroxyl groups associated with the polyol unit. It was found that all of the materials exhibited smectic A* phases, and that the clearing points increased monotonically with the number of hydroxyl groups. The linear increase was found to be independent of stereochemical structure and the degree of optical purity. A model suggesting that the smectic A* phase has an internal microphase separated structure can be used to account for these observations.

ISSN:0267-8292    

DOI:10.1080/026782998206272

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The synthesis and evaluation of a negative birefringence material which possesses a wide smectic C phase is reported.

ISSN:0267-8292    

DOI:10.1080/026782998206281

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

X-ray scattering studies were performed to elucidate the structure and the character of the correlations in a mesophase with two-dimensional positional order formed in a side group polymer. X-ray diffraction patterns of oriented fibres display weak diffuse lines in the direction parallel to the orientation of the side groups and a regular pattern of strong diffuse spots in the perpendicular direction, indicating positional order on the local scale. The side groups are close packed within a two-dimensional (2D) centred orthorhombic lattice and are tilted with respect to their nearest neighbours. The positional order is anisotropic and is limited by a correlation length of about 30-40A, that is approximately six involved in the short range order. In the direction along the normal to the 2D system shows no translational order. This phase displays the same unit cell symmetry and direction of tilt as the layers of the K phase and is designated as TDK, where the first two letters stand for 'two-dimensional'. Unexpectedly, we found a regular pattern of weak diffuse spots in the small angle scattering region. These indicate a short range modulated structure with the vector of modulation lying in the plane of the 2D packing of the side chains is proposed to explain the formation of modulated structure and the anisotropic character of the positional correlations. to eight side groups are plane, the order. A simple model of the

ISSN:0267-8292    

DOI:10.1080/026782998206290

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

4-Substituted phenyl-4-hexadecyloxybenzoates and 4-hexadecyloxyphenyl-4-substituted benzoates were prepared and thermally characterized by differential scanning calorimetry. Transition temperatures were identified by polarized-light microscopy. Substituents were chosen to cover a wide range of electronic and dipolar characteristics. Binary mixtures of different components were prepared and similarly characterized to construct their phase diagrams. In mixtures of the 4-CN and 4-NO2 analogues, enhanced SmA mesophases were found when either of these esters was mixed with one of the methoxy analogues. A weak molecular complex is proposed to account for this non-ideal solution behaviour. Linear or slightly enhanced mixture behaviours were found for the nitro or cyano derivatives when mixed with each other. The results are interpreted in terms of electronic, dipolar, and molecular interactions.

ISSN:0267-8292    

DOI:10.1080/026782998206308

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Phase diagrams of different substituted acids with 1-heptyl-4-(4-pyridyl)pyridinium bromide were investigated. The formation of ionic hydrogen-bonded 1 :1 and 1:2 associates can be detected in the solid state. In some cases thermodynamically stable smectic A phases are observed. The maximum phase stability in the liquid crystalline state can differ considerably from the expected value for the 1 :1 associates. The layer thickness of the smectic layers measured by X-ray methods is smaller than the value calculated from molecular models. This indicates a complicated packing behaviour of the molecular building units in the SmA layers.

ISSN:0267-8292    

DOI:10.1080/026782998206317

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Molecular mechanics (MM) calculations of the structure formed by bis(hydroxydimethylsilyl)methane [(CH3)2(HO)Si]2CH2(MDCS) molecules have been performed. The calculations lead us to conclude that MDCS can form a columnar liquid crystalline phase which consists of supramolecular H-bonded associates similar to those found earlier for siloxane compounds of the same type. Synthesis of MDCS was performed. IR, NMR, DSC and XRD (powder and single crystal) investigations have shown the existence of a LC phase in a narrow temperature range. The computational and experimental results suggest the existence of similar columnar LC phases in a wider temperature range for Et-, Pr-, and Bu-substituted bis(hydroxydialkylsilyl)methane.

ISSN:0267-8292    

DOI:10.1080/026782998206326

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A non-local description of nematic liquid crystals is presented. By considering a generic two body interaction, the total energy of a nematic sample is formally evaluated. It is given by a generalized non-local functional. The minimization of the total energy shows that the actual nematic tilt angle profile, characterizing the nematic director, is a solution of an integral equation that in the simplest case is of the Freedholm type. This new equation takes the place of the well known Euler-Lagrange equation used in the elastic theory of nematic liquid crystals. The existence of sub-surface deformations localized close to the limiting surfaces is studied by means of this integral equation. The analysis has been performed for cases of strong and weak anchoring, with and without external fields. The sources of the subsurface deformations are discussed in the framework of the usual Frank elastic theory.

ISSN:0267-8292    

DOI:10.1080/026782998206335

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The orientational behaviour of nematic compounds having twin phenylbenzoate mesogens was examined under a wide range of a.c. electric fields (0-2 V mum-1 and 10Hz-50 kHz). For this study, crossed polarizing optical microscopy (POM) and real-time X-ray diffraction (RTXRD) measurements were employed to investigate optical and orientational response. These nematic compounds have a positive dielectric anisotropy and a relatively low epsilon// relaxation frequency which allowed study in both homeotropic and planar orientations over a controllable frequency range. The optical behaviour and X-ray results corresponded well, providing a tool for understanding the orientational behaviour of these liquid crystals. For homeotropic alignment, an electric field of over 1 V mum-1 was required in order to obtain good orientation. However, homeotropic orientation depended on a delicate balance between thermal fluctuations and dielectric torque imposed by the electric field, which are both strongly related to the elasticity of the LC domains. Due to this effect, the highest orientation parameter achieved for homeotropic orientation was only 0.48, which indicated that this state was still non-equilibrium. On the other hand, for planar orientation, a uniform texture with orientation parameter of 0.65 was easily obtained even at electric fields as low as 0.2 V mum-1. The application of an electric field stronger than 1 V mum-1 induced a distortion in the texture, and reduced the orientation parameter to 0.45 for planar alignment.

ISSN:0267-8292    

DOI:10.1080/026782998206344

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A new series of chiral mesogens: (R) 4-(1-methylheptyloxycarbonyl)phenyl 4-(4-alkyloxyphenyl)ethylylbenzoates has been synthesized. All materials are mesomorphic and the liquid crystalline properties were characterized by optical observation, DSC and electro-optical measurements. They display SmA and ferroelectric SmC* phases at low temperatures. One of them, the nonyloxy derivative, exhibits the SmC*alpha phase, present in different 'antiferroelectric' series. This behaviour is confirmed by mixture studies. Furthermore one compound of the series, the heptyloxy derivative, C37H48O5 crystallizes in the P21 space group (Z=2) with the following parameters: a=8.497 (1), b=5.490 (1), c=36.148 (4)A with beta 92.72 (1). The final R and wR reliability factors were equal to 0.109 and 0.124, respectively; the goodness of fit was equal to 3.0. The whole molecule is L-shaped with the long chiral chain almost perpendicular to the core moiety as observed for several compounds showing an antiferroelectric mesophase. In the crystal, the molecules related through the 2 1 axis, located at z=0.5, give an antiparallel smectic C-like arrangement. The thickness of the sheets is equal to the c parameter, with a tilt angle close to 35. There are strong intersheet interactions between the chiral chains related through the 2 1 axes located at z=0 and 1.

ISSN:0267-8292    

DOI:10.1080/026782998206353

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor