Hitoshi Mada

Alignment of Liquid Crystals on the Stretched Polymer Films

Abstract Several kinds of the stretched polymer films, such as those of cellulose, polyvinylalcohol, and polyethylene are shown to have aligning capability for nematic liquid crystals (a mixture of cyanobiphenyls) in the direction of the stretching when the films are stretched over about 100%. Among them polyethylene is only one exceptional case where the initial aligning property lasts only for several days at room temperature.

Study on the Surface Alignment of Nematic Liquid Crystals: Temperature Dependence of Pretilt Angles

Abstract A simple phenomenological theory is presented for the surface or interface of nematic liquid crystals in terms of the surface order parameter μu. The theory is based on the existence of an easy axis at the surface, so that the surface order parameter is not only a function of a director but also the easy axis. Taking into account the concept of an easy axis field, the temperature dependence of pretilt angle can be expressed both for the free surface and the interface between liquid crystals and solid substrate. Two typical experimental results of temperature dependent angle obtained by Bouchiat and Langevin-Cruchon, and Toda, Mada and Kobayashi are compared with the theory, and good agreements are obtained qualitatively between them.

Wavelength and Voltage Dependences of Refractive Indices of Nematic Liquid Crystals

Abstract Refractive indices of a mixture of nematic liquid crystals as functions both of wavelength and applied voltages were measured. The measured results are compared with a theoretical calculation in which first the distributions of tilt angle of the molecules were computed by solving a reorientation equation, then, the effective refractive indices were computed from this distribution using an index ellipsoid. It is shown that the agreement between the experimental measurements and the calculated values are fairly good within the experimental error.

Surface and bulk order parameters of a nematic liquid crystal

The measurements of the anisotropy of the refractive index have been made for heptyl‐cyanobiphenyl (7CB) at the surface as well as in the bulk by the interferometric method. Using these data, order parameters S at the surface and S in the bulk were calculated. The results show that S is slightly larger than S in the nematic temperature region. S becomes zero in the isotropic region; nevertheless, the order parameter at the surface, S, still has a finite value even at temperatures above the clearing point.

Control and elimination of disclinations in twisted nematic liquid-crystal displays

A method for controlling and eliminating reverse-twist and reverse-tilt disclinations in twisted nematic cells without using cholesterics has been developed both theoretically and experimentally. Pretilt angle and tilting direction as well as twist angle and sense have been correlated with the appearance of disclinations. It is shown that for practical twisted nematic cells having a special sense of pretilt, the disclination free cells are realized by adopting the pretilt angle of 1°-5° and the twist angle of 80°-85°.

Time response of a nematic liquid‐crystal cell in a switched dc electric field

When a nematic liquid‐crystal cell is driven by a dc electric field, the capacitance of the cell increases in the first several tens of milliseconds, but after that the capacitance tends to decrease with a rather long relaxation time of the order of 1 s. This phenomenon can be explained by impurity ions which form the electrical double layer at the surface. The results calculated using this simple model qualitatively agreed with the exprimental results. The amount of charge in the double layer and the ion mobility are derived as 2×1011 ions/cm2 and 2.7×10−7 cm2/V s, respectively.

Architecture for optical computing using holographic associative memories

A new architecture for optical computing is proposed, based on associative memory which can be conveniently constructed by optical holography. This architecture is derived from a metaphorical model of the minor hemisphere of the human brain. We describe the performance of high-level intelligent information processing such as image processing, pattern recognition, concept formation, game playing with learning, and dynamic association.

Surface Order Parameter of 4-n-Heptyl-4′-Cyanobiphenyl

Abstract We measured the order parameter near the interface between a liquid crystal and the solid substrate treated by several methods. The interfacial order parameter is different according to the surface treatment, and is larger than the bulk order parameter. Moreover, in the temperature above the clearing point, the interfacial order still has a finite value.

Dielectric Properties of n-Pentyl-p-n-Cyanobiphenyl in Wide Frequency Range

Frequency dependence of the dielectric constant was measured for n-pentyl-p-n-cyanobiphenyl in the nematic phase. Two dielectric relaxations appear. The relaxation at high frequency is due to molecular motion; and the relaxation at low frequency is due to the ion drift, of which the relaxation time can be estimated as 8 s. Conductivity due to ion drift can also be obtained from the imaginary part of the dielectric constant to be on the order of 10-9 S/m.

Study on the Surface Alignment of Nematic Liquid Crystals: Determination of the Easy Axis and Temperature Dependence of its Field Energy

Abstract The assumption which was described in the previous paper1 has been proven in this paper. Namely, the easy axis is determined by means of the van der Waals forces for the free surface of liquid crystals and for the interface between a liquid crystal and an anisotropic solid surface. The energy of the easy axis is discussed and it is proven that this energy varies as the surface order parameter with temperature.