Haruyoshi Takatsu

Synthesis and properties of azo dye aligning layers for liquid crystal cells

The synthesis and properties of azo dyes that can be used for photoaligning liquid crystals (LCs) have been investigated. The structures and the synthetic procedure for the azo dyes are presented. The photoaligning of azo dyes takes place purely due to the reorientation of the molecular absorption oscillators perpendicular to the UV light polarization. The qualitative model for the phenomenon in terms of the rotational diffusion of the azo dye molecules in the field of the polarized light is discussed. The order parameters S = -0.4 (80% of the maximum absolute value S m = -0.5) were measured from the polarized absorption spectra at the wavelength 372 nm. A temperature stable pretilt angle of 5.3° was obtained by a two-step exposure of the azo dye film using normally incident polarized light followed by oblique non-polarized light. The azimuthal anchoring energy of the photoaligned substrate was Aϕ , 10−4 J m−2, which is the same as the anchoring of the rubbed polyimide (PI) layer. The voltage holding ratio value of a photoaligned LC cell was found to be even higher than for a rubbed PI layer, which enables the applications of azo dyes as aligning layers in active matrix liquid crystal displays. The thermal stability of the photoaligned azo dye layers is sufficiently high, but UV stability has to be improved, e.g. by polymerization. A new LCD aligning technology based on polymerized azo dye layers is envisaged.

Mesogenic Polymer Stabilized Ferroelectric Liquid Crystal Display Exhibiting Monostability with High Contrast Ratio and Grayscale Capability.

We have fabricated a new ferroelectric liquid crystal (FLC) display that exhibits monostable electrooptical characteristics with high contrast ratio (160:1) owing to freedom from defects, grayscale capability without threshold, and fast response (70 µs). A FLC(ZLI-4654-100, Merck) is subjected to polymer stabilization by UV photocure of a mixture of doped monoacrylates with a mesogenic side chain particularly at a temperature where the LC medium is in the SmC* phase under the simultaneous application of a monopolar electric field.

Liquid Crystalline Polymer Stabilized FLCDs with Conventional Rubbed Polyimide Films or with Photo Alignment Films of Poly(vinyl Cinnamate)

Abstract Polymer stabilized SSFLCDs have been successfully fabricated. A liquid crystalline polymer network in a device cell is formed by the photo-cure of UV photo-currable liquid crystalline monomers that are doped in an FLC, where both the rubbed polyimide (PI) and non-rubbed but linearly polarized UV irradiated poly(vinyl cinnamate) (PVCi) films are utilized as surface FLC molecular alignment. The actual monomers adopted is acrylate with a mesogenic side chain. The PVCi is one of the photo alignment polymer. The fabrication process of these SSFLC cells is as follows; first the photo-cure is done on a monomers and initiators doped LC medium at the temperature where this material takes SmA phase and then the cell is cooled down to room temperature, at which the medium takes SmC* phase. The layer structure of the liquid crystalline polymer stabilized (LC-PS) FLC cells has been investigated by X-ray diffraction measurement. As the experimental results, it is found that the formed polymer network suppresse...

Physical Properties of Nematic Tolans

Abstract A series of 4-n-alkyl-4′-n-alkoxytolans, trans-4-n-alkylcyclohexyl-4′-n-alkyltolans and 4-n-alkyl-2′- or 3′-substituted 4′-n-alkoxytolans was prepared. Their mesomorphic and physical properties were measured. Some nematic mixtures of 4-n-alkyl-4′-n-alkoxy-tolans and other familiar series of nematic mixtures of two-ring systems having n-alkyl and n-alkoxy as terminal groups were prepared and their physical properties were compared. A nematic mixture of tolans has a high N-I transition temperature of 72[ddot]C, a high birefringence of 0.297 and a low viscosity of 19.1 c.p. at 20[ddot]C. The birefringence and the flow-aligned viscosity of trans-4-n-propylcyclohexyl-4′-n-butyltolan were determined by extrapolation and compared with those of trans-4-n-pentylcyclohexyl-4′-ethylbiphenyl and 4-n-propylphenyl 4′-n-propylcyclohexyl-benzoate. The influence of the introduction of 2′-, 3′-fluoro and 2′-, 3’ -methyl groups into 4-n-alkyl-4′-n-alkoxytolans on the dielectric constants was discussed.

New developments in liquid crystal photo-aligning by azo-dyes

Liquid crystal (LC) photo-alignment using azo-dyes is reviewed. This alignment method is very different from previously reported ones, which are due to mechanisms such as photo-crosslinking, photo degradation, and photo-isomerization. We present the basic physical mechanisms of the photo-induced orientational order in various photo-aligning materials and in azo-dye layers in particular. This method is based on rotational diffusion in a potential created by the light field as well as intermolecular forces. It will be shown that this photo-aligning method can provide a controllable pretilt angle and strong anchoring energy of the LC cell, as well as having high thermal and ultraviolet (UV) stability. The application of this method to the alignment and fabrication of various types of LC displays is also discussed.

Photo‐aligning by azo‐dyes: Physics and applications

Liquid crystal photo‐alignment using azo‐dyes is reviewed. This alignment method is very different from previously reported ones, such as photo‐crosslinking, photo degradation and photo‐isomerization. It will be shown that this photo‐aligning method can provide a controllable pretilt angle and strong anchoring energy of the liquid crystal cell, as well as high thermal and UV stability. The application of this method to the alignment and fabrication of various types of liquid crystal displays is also discussed.

Effect of Polymer Network Made of Liquid Crystalline Diacrylate on Characteristics of Liquid Crystal Display Device

We investigated the effect of the polymer network, which is made of a liquid crystalline diacrylate in a nematic liquid crystalline host, on the alignment and motion of liquid crystals. We found that the polymer network has strong influence on the alignment and motion of the liquid crystals even with the low concentration of 2 wt% of the liquid crystalline diacrylate. The polymer network prepared in an electric field gives a uniform alignment of liquid crystals with a tilt angle to the alignment layer because of good orientation of the polymer network. Furthermore, we report the effect of the oriented polymer network on the characteristics of a twisted nematic (TN) device.

Photoaligned Vertical Aligned Nematic Mode in Liquid Crystals

The photoaligned vertical aligned nematic (VAN) mode in liquid crystals (LC) was developed using the photosensitive polyimide (PI) JALC 2021-R2, illuminated by obliquely incident nonpolarized light. It has been found that the combination of PI with water soluble sulfonic azo-dye (SD) yields a perfect electro-optical performance of a liquid crystal in the VAN mode. The polar and the azimuthal anchoring strengths of LC in VAN mode were measured both for rubbed and photoaligned surfaces. Increasing the illumination time results in the exponential growth of the contrast ratio in the VAN LC cell. Analysis of anchoring strength and electrooptic behaviour of the photo-aligned LC cells confirm that the mechanism of photo-alignment in our materials includes not only the photodegradation, but mostly the reorientation of both SD-1 and PI molecules to get the average absorption oscillator almost parallel to the direction of the obliquely incident UV light.

Novel mesogenic polymer stabilized ferroelectric liquid crystal display device exhibiting V-shaped electrooptic characteristics

By using a conventional commercially available ferroelectric liquid crystal (FLC), FELIX M4851/100 (Clariant Japan), which is doped with newly developed photocurable mesogenic liquid crystal monomers, 2A363 (DIC), a new FLC device exhibiting V-shaped electrooptic performance is successfully fabricated. In the fabrication process, the photocure is carried out in the smectic A phase without applying an external voltage and the mesogenic monomers may form a polymer network.

Fabrication and electro-optic characteristics of polymer-stabilized V-mode ferroelectric liquid crystal display and intrinsic H-V-mode ferroelectric liquid crystal displays: their application to field sequential fullcolor active matrix liquid crystal displays

Shunsuke KobayashiJun XuHirokazu FurutaYuji MurakamiSatoru KawamotoMasafumi Oh-kouchiTokyo University of ScienceLiquid Crystal Institute and the GraduateSchool of Engineering ScienceYamaguchi, OnodaYamaguchi 756-0884, JapanHiroshi HasebeHaruyoshi TakatsuDainippon Ink. and Chemical Ind.Ina-machi, Kitaadachi-gunSaitama 362-8577, JapanAbstract. We fabricate ferroelectric liquid crystal display (FLCD) de-vices exhibiting a thresholdless V-shaped switching by adopting a me-sogenic liquid crystal polymer stabilization and also FLCDs exhibitinghalf-V-shaped switching using an undoped FLC material. These FLCDsare respectively called polymer-stabilization (PS)-V-mode FLCDs and in-trinsic H-V-mode FLCDs. By using especially developed polyimide ma-terials such as RN-1199 and RN-1411 series (from Nissan Chem., Ind.)for the surface alignment and together with a well-controlled rubbingtechnique, photoalignment, and ion-beam alignment, we succeed in fab-ricating zigzag defect-free FLCDs. In particular, the PS-V-mode FLCDfabricated in this way exhibits continuous operation with a high contrastratio of 700:1, and the intrinsic H-V-mode FLCD has good temperaturestability by using the combined alignment technique. Particularly, a field-sequential full-color (FS-FC) LCD using PS-V-mode FLCD shows goodlong-term stability for a continual operation. Using these FLCDs, we alsodevelop several prototype models of FS-FC active matrix LCDs with thespecification of video graphics arrays (VGAs) and extended graphicsarrays (XGAs), where we take advantage of their high-speed response(time constants 100 to 500 ms).