Development of the Nematic Liquid Crystal Compounds Derived from Phenyl Acetylene Group with Large Birefringence

Abstract

Novel liquid crystal compounds with extraordinary large birefringence have been studided from the viewpoint of optical anisotropy. A large birefrinence was obtained in the compounds compared with that in 5CB, while the orientational order parameters determined by FT-IR measurement are almost the same. From the calculated results of molecular polarizability, it is concluded that the large optical anisotropy is mainly caused by the electric anisotropy.     

Liquid Crystal Television

The application of liquid crystal to display devices was first proposed by Heilmeier et al. in 1968, and a liquid crystal television (LC-TV) addressed by electron beam was made as a trial in the same year. Since then, it has taken about 15 years for practical LC-TVs to be developed. Full-color, higher resolution and greater pixel number have been attained, and presently, at least for small size LC-TVs, image quality has become very close to that of CRTs.     

Ukranian Liquid Crystal Society

Abstract

The Third Ukrainian Liquid Crystal Conference, was held in Kiev, at the Institute of Physics, 10 and 11 January, 1995. More than 50 delegates, representing 12 liquid crystal scientific and industrial groups working in the Ukraine, discussed the latest achievements in physics, chemistry and application of liquid crystals.     

Liquid Crystal Display Research in Japan

The technology development of liquid crystal display started having a remarkable influence on the technology innovation of up-to-date electronic calculator. While a digital display using liquid crystal display has been developed in its earlier stage as the segment type which sets a limit of display to numeric and certain symbols, it is also spent an effort to develop the X - Y matrix type which can display alpha-numeric and moreover kana characters. As a practical application of the X - Y matrix type liquid crystal display, an alpha-numeric type scientific electronic calculator and electronic translator will be reported.

Further, the present status of liquid crystal display applications and trend of R&D in other consumer and industrial electronic industries in Japan will be reported. Finally, activities in the Japanese academic circles will be presented.     

Reentrant Phenomenon in Disc-Like Liquid Crystal

Several Hexa-n-alkanoates of truxene with long alkyl chains exhibit, above and below a N_D nematic phase, an hexagonal columnar phase. It is probably the first example of a reentrant phenomenon for pure disc-like liquid crystals at atmospheric pressure.     

Guest-Host Type Liquid Crystal Displays

Eight modes of the guest-host cells (GH-cells), in which types of dye, liquid crystal and their alignments are adequately combined, are surveyed, and the color contrast of each mode is calculated.

Three modes among them are of positive type display, that is, colored patterns on the colorless background contrary to the initially proposed fundamental GH-cell. Another three modes are the GH-cells without polarizer, by which bright display can be obtained.

Light stability of dyes are also discussed and lifetimes of various dyes are estimated by accelerated life test. As a result, it is found that diazo-and axomethine-dayes without thiazole groups as well as anthraqunone-dyes have satisfying lifetimes as long as they are used indoors.     

First Truly Ferroelectric Liquid Crystal

The first faroelectric liquid crystalline phase (in 8SI* (ΔS-(+)-(4-(2′methylbuty1) phenyl-4′-n-octylbiphenyl-4 carboxylate) is reported and its physical properties are discussed. The close connection between the phase sequences of 8SI* and its racemate are established. Both compounds show a number of smectic phases above the newly discovered ferroelectric phase and its analogue in the racemate. These phases (CI and G') are tilted in the racemate 8SI and tilted with a helicoidal structure in 8SI*. In the truly ferroelectric phase, X, the director of the molecules can be oriented in a bistable way in an electric field Furthermore when the field is turned off the director orientation remains unchanged. This behaviar is fundamentally different from that in bulk smectic phases which support the helix structure in the absence of external forces. A model far ‘racemates’ in higher smectic phases like G, G', H’ etc as well as a the newly discovered ferroelectric phase is presented. The response of cholesteric blue phases of 8SI* to an external field is discussed in an appendix.     

Blue Phase in Liquid Crystal Polymer Mixtures

Blue phases are observed in mixtures of a low molecular weight cholesteric and a nematic polymer. Phase diagrams, optical properties and textures of these mixtures are reported and compared to the case of low molecular weight cholesteric-low molecular weight nematic mixtures.     

Color Gamut of Liquid Crystal Polysiloxanest

Polysiloxanes with suitable side-chains form a cholesteric liquid crystal phase that can be applied to a substrate to produce a durable coating which exhibits strong colours below the glass transition temperature. The peak reflectance is almost 0.5 and a nearly 1.0 peak reflectance can be obtained using a half-wave retardation plate coated on both sides with the material and viewed from one direction against a black background. Values below 0.5 and between 0.5 and 1.0 have been also obtained using suitable solvents and alignment techniques. Many desired spectral reflectance distributions can be then obtained because of the additive color properties of such cholesteric coatings. As a result it is possible to produce a larger colour gamut than with real surface colours such as pigments and dyes. Employing commercially available material experimental work was carried out demonstrating a greatly expanded colour gamut on the chro-maticity diagram. Also it is possible to modify the spectral reflectance distribution of coloured substrates by coating them with a material having a reflectance peak at the desired band of wavelength.     

Light-Induced Instabilities in Photo-Oriented Liquid Crystal Cells

In a planar liquid crystal sample sandwiched between a photosensitive and a reference plate instabilities occurred, when the cell was illuminated from the reference side. The instabilities were induced both by polarized white light source and monochromatic laser beams. Static and dynamic regimes were found; for laser irradiation dynamic instability was found only in a range of polarization directions. A model, developed for monochromatic excitation, predicts that at certain thicknesses dynamic instability is forbidden. Experiments on a wedge-like cell confirmed this conclusion.     

Bowlic and Polar Liquid Crystal Polymers

Bowlic liquid crystals are made up of polar molecules. Both main-chain and side-chain bowlic polymers are possible. Exactly solvable discrete models describing the phases and conformations of these bowlic and other polar liquid crystal polymers are presented. For the ideal one-dimensional case the model is equivalent to the 1D Ising model. Susceptibility and other properties are calculated. Wave propagation and solitons in these polar polymers are discussed. Possible highly conducting and high T_c superconducting liquid crystal polymers are proposed.     

Material Highlights: Liquid Crystal Polymers

Abstract

A key issue in the area of side chain liquid crystal polymers concerns the conformation of the backbone within the mesophase. In order to resolve this matter, Noirez and co-workers (Liquid Crystals, 1995, 18 129) have studied a wide range of polymers exhibiting both nematic and smectic behaviour using small angle neutron scattering. Their results combined with a survey of those in the literature reveal that if the polymer is solely nematogenic, then the backbone adopts a prolate conformation in which on average it lies along the director. By contrast, in a smectic phase the backbone adopts an oblate shape and on average lies perpendicularly with respect to the director. This arises from a microphase separation in which the backbones are distributed between the mesogenic layers. However, the backbones can cross the mesogenic layers although their ability t o do so depends on, amongst other factors, the degree of polymerization. If the polymer exhibits both nematic and smectic behaviour, then in the nematic phase the backbone adopts a slightly oblate shape resulting from smectic fluctuations.     

Ad-Ad Transition in a Binary Liquid Crystal System

Miscibility, high pressure, Xray and dielectric studies on binary mixtures of terminally nitro and cyano substituted compounds are presented. The results show the existence of the A_d-A_d transition which occurs from a partially bilayer phase with a temperature-dependent layer spacing to another with a temperature-independent layer spacing.