Taisaku Nakata

Homeotropic reverse-mode polymer-liquid crystal device

We have proposed a new type of reverse-mode polymer-liquid crystal device: homeotropic reverse-mode polymer-liquid crystal (HRPLC). This device consists of a liquid crystal with a dielectric constant having negative anisotropy and a pair of glass plates covered with a homeotropic alignment layer. The HRPLC’s operation is the reverse of the usual; i.e., it is clear when no voltage is applied and opaque under applied voltage. We have confirmed that the HRPLC operates well in reverse mode and have studied the dependence of its properties on liquid crystal material, curing process, and cell thickness. Experimental results indicate the HRPLC has a 30:1 contrast ratio over an operating voltage range of 0–11 V. In special fabrication conditions, the transmittance–voltage curve of the HRPLC drops to a minimum at a certain voltage level and begins to increase at that point. We have proposed a model to explain this result.

Metal-ligand bonding properties of double-sided porphyrin complexes : influence of bulky ester groups

Metal–ligand bonding properties of double-sided porphyrinato-iron(II) and -cobalt(II) complexes have been characterized by ESR, IR, and Mossbauer spectroscopy. The smaller AN value for a 1-methyl-imidazole (mim) adduct of 5,10,15,20-tetra(2,6-dipivaloyloxyphenyl)porphyrinatocobalt(II) compared to that of 5,10,15,20-tetra(2,6-di-tert-butylacetoxyphenyl)porphyrinatocobalt(II) suggested that the cobalt–imidazole bond is weak. The ESR spectrum of the dioxygenated double-sided series in fluid toluene indicated that an electrostatic interaction between the bound dioxygen and the ester fences was rarely found. The relaxation of steric strain on the rear side of the ring plane for axial imidazole bonding resulted in a lowering of the bound CO and O2 stretching frequencies of iron(II) complexes. This indicates that the π-back donation from the dπ orbital of the iron to the π* orbital of the bound gaseous ligand could be controlled by the strength of the iron–imidazole bonding, which is regulated by the structure of the rear pocket on the macrocycle. The co-ordination structure of various ligands in double-sided porphyrinatoiron complexes is also discussed by means of Mossbauer parameters.

Liquid crystal photo-alignment layers made from aromatic bismaleimides

We propose a new type of liquid crystal photo-alignment layer made from aromatic bismaleimides. Aromatic bismaleimides are expected to react anisotropically by irradiation of polarized ultraviolet (UV) light. In the fabrication process of the new photo-alignment layers the curing process is much shorter than that needed for conventional polymeric types of photo-alignment layers. We have proved that the use of aromatic bismaleimides enables liquid crystal molecules to be aligned homogeneously by irradiation of polarized UV light. In particular N,N′-p-phenylenebismaleimide shows good photo-alignment characteristics and high UV sensitivity. In studying the relationship between molecular structures of aromatic bismaleimides and photo-alignment properties, we find that aromatic bismaleimides that have a linear molecular structure and resonance structure produce good photo-alignment layers.

Polymer Morphology and Electro-Optic Properties of Psct Devices

Abstract The relations between the polymer morphology and electro-optic properties in polymer stabilized cholesteric textures (PSCT) were investigated. SEM analysis revealed that the polymer matrix consisted of submicron-orderdiameter spherical particles, which are connected with each other and forms three-dimensionally networked wire. The network spacing which evaluated from a number of the polymer particle in volume was the main factor determining the electro-optic characters of the device. With the larger network spacing, the improved properties of PSCT device such as lower driving voltage and higher contrast ratio were attained.

22.2: RGB-Stacked Holographic Polymer Dispersed Liquid Crystal Device for Color Reflective Display

In stacking holographic PDLC devices, the parallax in the stack and the viewing angle should be considered. Based on a thin glass substrate (thickness = 0.1mm) assembly technique and an optical setup with a lenticular-lens array, RGB-stacked HPDLC devices with a low parallax and a large viewing angle (>15 degrees) have been developed.