Satoshi Niiyama

Phase diagram and phase separation in LC/prepolymer mixture

A new method to obtain liquid crystal and polymer composite(LCPC) material is reported. This material is a new electro-optic material which can control scattering and transparent states in an electric field. e obtained this material by the photo-polymerization-induced phase separation from liquid crystal and prepolymer mixture where both monomer and oligonier are used as prepolymer. We have found new type of phase diagram in this mixture which has a nematicisotropic line in addition to binodal and spinodal lines. Electro-optic properties of this material are strongly affected by the point on the phase diagram at which the polymerization-induced phase separation starts. This method enables us to control these properties such as voltage-transmittance characteristics. Typical devices using these materials are also shown. They have high contrast ratio and high transmittance in ON state and are suitable for display devices. Drive voltage can be reduced by optimizing this material and the device with high contrast ratio about 200:1 in low drive voltage below 6Vrms was obtained.

Optical Microscopic Observation of Morphology in Liquid Crystal/Polymer Composites and Their Electro-Optical Properties

We have discovered that bicyclohexyl is suitable for extracting liquid crystals from liquid crystal/polymer composites consisting of a continuous phase of nematic liquid crystal and a three-dimensional polymer network. It was confirmed in optical microscopic observation for the morphology of composites that a polymer structure, observed after extraction of liquid crystals from composites by bicyclohexyl, accorded well with the structure observed by a non-destructive method at a higher temperature than the nematic–isotropic transition point of the liquid crystal. The relationship between the polymer structure in the composite which was evaluated by the non-destructive method and the condition of phase separation induced by photo-polymerization was closely investigated from an aspect of a phase diagram and the speed of phase separation controlled by the intensity of irradiation by UV light. The electro-optical characteristics of the liquid crystal/polymer composite cells were found to be strongly affected by the polymer structure, especially the pore size of the three-dimensional network, which was especially sensitive to the intensity of UV light.

Three-dimensional morphology of LCPC using confocal fluorescence microscopy

We have developed a new method for characterizing morphology of LCPC based on confocal fluorescence microscopy. Not only two-dimensional but also three-dimensional morphology of LCPC can be observed nondestructively by this method. The morphology of LCPC was consisted of liquid crystal and polymer phases, both of which are three-dimensionally continuous. Quantitative analysis of morphology was also made to clarify the relation between morphology and electro-optical characteristics. The local size of structure was obtained quantitatively from the perimeter of liquid crystal and polymer. It was found that the change in the value matched well with the change in morphology and it was related with the electro-optical characteristics.

Morphology and ordering control in LCPC

A phase separation under an applied electric field (PSUF treatment) in LCPC relaxes the energetic stress for dynamic operation of its device. Both higher dynamic response time and less hysteresis in dark gray scales which are significant issues in LCPC are achieved, since its treatment can control the interface between liquid crystal and matrix polymer without the damage to scattering in off state and contrast ratio. It is based on the morphological characteristic which is caused by the first step: a segregation of liquid crystal and ordering process of the liquid crystal under an applied field, and the second step: polymer/pre-polymer precipitation to maintain the early ordering of segregated liquid crystal. The essential structure of LCPC caused by the characteristic phase separation process, is characterized with confocal fluorescence microcopy, which also supports its process mechanism.

Display-Special Contribution from IDW '98. Reflective-type polymer dispersed LC-mode Projection Display.

A new compact projection display has been developed using light valves based on a 2-inch diagonal low-temperature poly-Si TFT reflective XGA array and polymer dispersed LC-mode, 120-W ultrahigh-pressure short-arc lamp (UHP lamp), and simple optical components. Luminous flux of 1400 ANSI-lm, contrast ratio of 85, and the illuminance homogeneity of 90% were achieved. Simulation by basic optical theory in concentrators and experiments with a simplified reflective-type polymer dispersed LC-mode light valve indicates that the performance could be improved in future up to a luminous flux of 1600 ANSI-lm with contrast ratio of more than 150.