Tomohisa Gotoh

Preparation and characteristics of new reverse mode film of polymer dispersed liquid crystal type

A reverse mode operation has been achieved in a polymer dispersed liquid crystal (PDLC) film by a novel methodology. A mixture of a dual frequency addressable liquid crystal (crossover frequency (fc): 13 kHz at 298 K), an acryl monomer and an acryl oligomer was irradiated by UV light under the application of an electric field [50 V, 100 Hz(≪fc)] to give a reverse mode PDLC film. The film thus prepared shows 95% transmittance in the absence of an applied voltage (OFF state), while the transmittance decreases to 5% by applying 50 V at 50 kHz (≳fc) (ON state). Upon removal of the applied voltage, the film transmittance returns to 95%. The response time (the ON time: 24 ms and the OFF time: 74 ms) are similar to those of normal mode PDLC films.

Electro-optic properties for liquid crystal phase gratings

A new type of liquid crystal device was developed by applying a concept of liquid crystal phase gratings (LCPGs). LCPGs are composed of square-wave phase gratings constructed with poly(methyl methacrylate) and liquid crystals which fill the grating grooves. The typical sizes of the phase grating are 10 micrometers in width and 2 micrometers in depth. The transmitted light wavelength can be easily controlled by changing applied voltage. The transmittance varied from less than 1 for monochromatic polarized light, when applied voltage varied from 0 V to 5 V. Rise times for the light varied from 0.2 ms to 7 ms with applied voltage, and were inversely proportional to the square of the applied voltage. Decay times, which depend slightly on the applied voltage, were about 4 ms. A transmitted light, i.e., an observed color (e.g., R,G,B and white), was dependent on not only applied voltage but also grating depth. When two of the LCPGs were combined in such a way that their grating lines were oriented perpendicular to each other, these LCPGs were applicable to nonpolarized light.

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.

Stabilization of Epoxy-Based Polymer-Dispersed Liquid Crystal Films by Addition of Excess Hardener

Abstract Polymer-dispersed liquid crystal (PDLC) films whose matrices consist of two-component epoxy resins have been studied. Their driving voltage and response time depend on the epoxy oligomer/hardener ratio in the epoxy resin. When an excess of the hardener (polythiol) is mixed in the epoxy resin, PDLC films which have the following superior properties have been successfully fabricated. 1) The driving voltages are lower than that of the PDLC film which contain an equal amount of the epoxy oligomer and the hardener. 2) The driving voltage and response time do not change with time. On the other hand, when an equal amount of the oligomer and the hardener are mixed in the epoxy resin, the driving voltage and response time of the PDLC film vary with the time. The driving voltage change of the PDLC films is related to the change of their admittance by the use of a two-phase model, in which spherical droplets are dispersed in the matrix.

Consumer Phase Shift Simulation Based on Social Psychology and Complex Networks

We have developed the methods for estimating how a new product or a new service will be accepted in contemporary society, considering the effects of word-of-mouth recommendations. These methods are based on a consumer phase shift modeling framework that consists of a consumer agent model and a social network model. Consumer agents, which are classified into four types and six phases, exchange information with each other on a social network. Model parameters were acquired by surveys regarding several new services. These surveys were designed using the snowball sampling technique. We also developed a network generation procedure, applying the idea of complex networks. The multi-agent simulation results proved the feasibility of this framework.

Consumer Behavior Modeling Based on Social Psychology and Complex Networks

Service innovation necessitates the acceptance by customers. The evaluation of the acceptance is problematic as word-of-mouth type of advertising becomes popular. We developed a consumer behavior modeling framework that consists of consumer agents and consumer network, using snowball sampling technique. The differentiating technologies are social psychology and complex networks. Our data analysis and multi-agent simulations proved the feasibility of this framework.

A Study on Extraction Method of Synonyms in Specification Documents

Recently, the document information managed in companies tend to be more complex and various. Specification documents are used for the technical transfer and inheritance of manufactures and services. However, the description and the meaning of the component words in specifications are often inconsistent or multiple, because a specification document is made by the persons in charge of various parts. Then the readers may misunderstand the contents of specifications by them. This paper focuses on synonyms, multiple description of words for a meaning or a word, in specification documents and proposes an extraction method of them considering the co-occurrence words of component words. This paper applies the proposed method to a test data, in which some words in an actual specification document are replaced with another words, and studies the effectiveness of the proposed method.

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.

Preparation and Optical Properties of a Reverse-Mode Polymer Dispersed Liquid Crystal Film

Two new types of reverse-mode polymer-dispersed liquid crystal films have been developed and successfully produced. The first was produced by UV-curing of a mixture of dual frequency addressable liquid crystal (DFALC) and UV-curable polymers under an applied voltage at a frequency lower than the crossover frequency (f c ) of the DFALC. This first type is referred to as a dual frequency type. The second type was produced by injecting a liquid crystal having negative dielectric anisotropy into a specially prepared porous polymer film from which liquid crystal having positive dielectric anisotropy had previously been extracted. The type thus produced through such “negative-for-positive” substitution is referred to as a substitution type. While the dual frequency type can not be driven at a low frequency, substitution type can, which gives it a distinct advantage. Other electro-optic characteristics of the two types of films, including alignment properties of the liquid crystal molecules, are also discussed.

Optical Design that Increases Light-Extraction Efficiencies of Organic Light-Emitting Devices through Finite-Difference-Time-Domain Method

The efficiency of light extraction in organic light-emitting devices is insufficient for practical use. This low efficiency is mainly attributed to the refractive index of the light-emitting layer. As the source of an organic light-emitting device is the sum of the point sources, and the wavelength of the emitted light and the scale of the optical structure are comparable, the near-field from the source plays an important role in determining the efficiency with which light is extracted in organic light-emitting devices. Finite-difference time-domain (FDTD) calculations were used to simulate conditions that could not be illustrated with ray optics. We found that the spherical Poynting vector of a point source becomes normal to the high index-ratio interface situated in the near field of the source, and this transformation of the Poynting vector results in the light-extraction efficiency being increased.