Kazuhisa Toriyama

New liquid‐crystal method for revealing ferroelectric domains

It was found that a layer of the nematic liquid crystal p‐N‐(p‐Methoxybenzylidene) amino n‐butylbenzen, extended on a triglycine sulfate crystal, takes on an orientational pattern which delineates the polarized domain structures. This technique quickly delineates domain structures in great detail and can be used on a wide variety of ferroelectric crystals. It is even applicable to a uniaxial regular type in which a domain structure cannot be detected by ordinary optical methods. The new method and the ordinary carbon powder pattern technique were compared on a triglycine sulfate crystal.

A new association model for nematogenic systems. Its significance for liquid crystal materials research

Abstract The importance of molecular association is considered in relation to the physical properties of a number of nematogens. It is proposed that association leads to the formation of polar and apolar dimers, which influence the dielectric and electro-optic properties of nematic liquid crystals. Dielectric and light scattering measurements of polar and apolar correlation factors are reported for a series of dipolar mesogens, and interpreted in terms of a model for molecular association. Both the solute molecular structure and nature of the solvent influence the degree of association, and the good device properties of mixtures of positive and negative nematogens is tentatively attributed to the strong tendency of dipolar solutes to associate in negative nematic solvents.

Dipole-Dipole Association of Polar Molecules in a Non-Polar Liquid Crystal Solvent

Abstract Measurements are reported of the permittivity as a function of temperature and composition for strongly dipolar cyano-substituted molecules dissolved in a non-polar nematic liquid crystal solvent. Solute molecules with dipole moments perpendicular to the molecular alignment axes exhibited strong parallel association of their dipoles, even at low concentrations, and the measurements can be interpreted in terms of a ‘strong dimer’ model. Results for a solute molecule with a large dipole moment co-linear with the long molecular axis gave the major dipole correlation factor equal to 1, consistent with little or no preferred dipole-dipole correlation.

A method of measuring the low tilt bias angle of liquid crystals

A new method of measuring the low tilt bias angles of liquid‐crystal displays is proposed. It is based on the threshold characteristics of magnetocapacitance, which vary according to the relative direction of the magnetic field and the directors. The tilt bias angle is determined completely by geometrical configurations and without any fitting procedure. The method ensures accuracy up to 0.1° in the present example. Threshold field variations due to sample rotation in the magnetic field are calculated from the theoretical magnetocapacitive curves, and experimental results are in good agreement with them.

Liquid Crystal System as Molecular Machinery: Investigation of Dynamic Impedance Matching between Molecular Core and Terminal Groups Using Rotor-Bearing Model

Liquid crystal phase stability is examined for liquid crystal terphenyls and their fluorinated derivatives, and some general rules are proposed that relate phase stability to molecular structures. A mechanical model is applied to explain the phase behaviours of these compounds. We postulate that liquid crystal phases are micromachine systems consisting of an ensemble of molecular rotors. The molecular core and terminals are the rotor and axes, respectively. The terminals also function as bearings for the subsequent layers molecular rotors. Phenomena of the thermal stability of phase and polymorphism are interpreted in terms of basic mechanical and dynamical parameters: centre of gravity, eccentricity, moment of inertia and mass distribution. The importance of dynamic impedance matching between parts, rotors, axes and bearings, is emphasized. Fluorination effects on liquid crystallinity are explained in a unified manner on a mechanical and dynamical basis.

Liquid crystal Lichtenberg figure

A new method for delineation of surface discharge figures on insulating surfaces is described. Cholesteric liquid crystal thin films on insulating surfaces finely delineate structures of residual charges of surface discharges on them. The method has high resolving power (∼ 1 μm) in the delineation of the surface discharges.

A design of multiplexing liquid-crystal display for calculators

A numeric liquid-crystal display using the dynamic scattering mode has been developed for calculators by adopting a total system design through the integrated development of material, device, and system. A mixed Schiff-base nematic liquid crystal with the dopants of l-hexadecylpyridinum bromide and p-aminophenol has been developed for the 1:2 selection multiplexing drive over a wide temperature range (0-40°C). A reliable package has been achieved with new technology. A 1-chip CMOS driving circuit with a 42-lead package has been developed for 8-digit 7-segment numeric readout displays in order to eliminate the dc component of the applied voltage, to minimize variations in the drive voltage, and to reduce power consumption. The devices have passed severe reliability tests. Our displays have lasted 15 000 h under normal test conditions. Using the dichroic mirror approach, it has become possible to design color displays of yellow, green, blue, or any color which have high readability and wide viewing angle under severe ambient light conditions.

Mechanical String Model for Liquid Crystal Ensemble: A Comprehensive Model for Polymorphism

A mechanical string model is proposed for liquid crystal phase behaviour to comprehensively interpret the polymorphism phenomenon. In the proposed mechanical string model, the strings consist of many molecules existing among many layers in a smectic phase stretched perpendicular to the layers. The string itself induces self-excitation, a resonance between the strings vibrational mode and local molecular vibration or rotational motion, which in turn induces a phase transition from one phase to another phase at these resonance points. We propose a possible procedure for extracting and assigning a set of two parameters that represent the strings eigenvalue (energy term) and freedom of motion (entropy term) from the existing experimental data. The set of parameters or the code is a representation of the phase sequence or polymorphism of each liquid crystal. It is directed that such a code assignment of the ratios with rational numbers be originated in the mechanics of the string. The characteristic representations of the rational number sets for various liquid crystals are correlated to the molecular structures and their mechanical and dynamical characteristics.

Reliability of Liquid Crystal Display

This paper reports the reliability of twisted nematic liquid-crystal display for basic applications such as watches and calculators. We have studied significant stress factors such as voltage, temperature and humidity, and their corresponding failure modes. The main failure mode is LCD misalignment; many different modes appear corresponding to different stress conditions as well as material and process for the LCD. We have analyzed the accelerated test results by Weibull distribution, elucidated accelerating factors, and estimated life time. The life is inversely proportional to 1.78-2.45 power of applied voltage, depending upon misalignment modes. The distribution of life is well expressed by Weibull distribution with shape parameter between 2.5-3.0, and proportional to the square of coefficient of variation of life. We conclude that the acceleration factors could be determined and 99.9% of tested displays will live more than 10 years. The knowledge on reliability of LCD can be now applied to new fields of LCD, such as industrial use, home appliance, and automotive instruments.

Dye-type liquid-crystal displays

The progress of dye technologies for liquid-crystal display, which have been greatly expected to provide new characteristics to the LCD have been reviewed. First, we discuss optical properties of the cholesteric medium and their application to phase change guest-host LCDs. The electrooptical properties of this dye-type display are reviewed from the viewpoint of multiplexability, which is one of the key factors for real application. Basic technologies for a dye-type LCD such as the dye itself and the host LC are also discussed. Finally, we propose a new field of application for dye-type LCDs.