A highly twisted nematic liquid crystal display (LCD) exhibits bistability of thc; 'up' and 'down' states when a holding voltage is applied. This device has the advantage of low cost driving without using active elements. In this study, the bistable device is applied to reflective guest-host LCDs, and t.he EO performance and switching performance of the device is evaluated. We will demonstrate the good bistability and the fast switching speed of this display mode.
Electrically Controlled Birefringence (ECB) LCDs are one possible candidate for reflective color LCDS, because their color gamut is as wide as that of backlighted color LCDs. However, conventional LCD drive methods are not applicable on ECB LCDs. To increase the number of reproduction colors and realize full color reproduction, we proposed a new drive method for PCB LCDs using additive mixing of chromatic colores and achromatic colores. Furthermore, viewing performances of ECB LCDs using the new method are discussed.
Homeotropic guest-host(GH) mode cell is good for a reflective 3-layer GH-LCD because of its high reflection and good optical properties. In this paper, we investigated LC's orientation or optical properties of Homeotropic GH mode cell and compared with properties of Super-twist GH mode cell.
A new reflective display is proposed. This display is composed of a scattering film, a quarter wave plate,a vertically aligned cell and a reflector. The feature of this LCD is high multiplexibility and gray scale capability.
Reflective LCDs are greatly needed for the application of personal information appliances. Among various reflective LC modes currently proposed, we focused on the cholesteric texture (CT) mode for its high reflectance at a specific wavelength range and simple cell structure, that is, only a light absorption layer is required for the CT cell. To realize a high information display with the CT mode, an active matrix driving such as TFT is necessary. The low driving voltage is required for an active matrix driving. In this report we tried to reduce the threshold voltage of CT mode LCD by the adjustment of the cell design and the cholesteric liquid crystal materials.
We developed a parallax-free double layer guest-host liquid crystal cell. By introducing a polymer film as a separator of two guest-host cells, a high contrast and high reflectivity display can be realized without parallax problem. A prototype showed 60% transmittance and 7:1 CR. We describe this double guest-host cell structure, assembly process, and its optical characteristics.
We have developed the multi-sensing system for sensing an electric field and dcecomposition products by use of a nematic liquid crystal cell sandwiched between a pair of choresteric liquid crystal cells combined with the corner cube prism coated by a dye film. The electric field can be detected at the wavelength of the selective reflection of the choresteric liquid crystal. The decomposition gas can also be detected at the different wavelength region as spectra changes of the dye film deposited on the corner cube prism surfaces.
We have investigated an optical head using a liquid crystal device (LCD) as a new application. The wave front aberration caused by a disc tilt is reduced by using an LCD because an LCD can control refractive index by applying voltage. As a result, the optical disc tilt margin is expanded. In addition, we achieved a disc tilt servo and CD/DVD compatibility with one LCD.
An anamorphic liquid crystal (LC) microlens can be obtained utilizing LC molecular orientation effects in a nonuniform electric field produced by the elliptically-patterned electrode structure. Since the focal length in the direction of the major axis is different from that of the minor axis, the anamorphic LC microlens is useful for the application to the collimation of an astigmatic beam emitted from a laser diode. In this work, we measured and estimated the aberration properties of the anamorphic LC microlenses, and discussed an optimization of the device parameter dependence in order to achieve the spherical aberration-free condition.
The distribution of refractive index can be controlled by provided External Controlling Electrodes (ECE). Variable focusing performances and deflection function of liquid crystal cylindrical-microlens with ECE are demonstrated. Shift in the focal point are obtained about 11μm and variable focusing performances are improved.
Beam steering properties of a liquid crystal microlens with a divided hole-patterned electrode structure in 8 regions are investigated. We can obtain the larger beam steering function maintaining nearly parabolic refractive-index distributions. As a result, spot shifting properties are improved in comparison with our previous work.
We can easily obtain electrically tunable lens and/or prism as novel optical active devices by usingliquid crystal materials. In this work, we try to use the liquid crystal prmsm as a beam splitter of the lateral shearing unterferometer. A considerably larger size of birefringent prism can be easily obtained by adopting wedge cell structure, and the shearing value; that is, the sensitivity and dynamic range of the measurement system can be electrically controlled. It us demonstrated that this simple system can successfully be applied to measure the thickness of the Al evaporatton thin film.
We present a new optoelectronic feed-forward neural network system which is able to train the network according to delta-rule without using any external computers. This neural network system is composed of Spatial Light Modulators using Ferroelectric liquid Crystal. This optical system calculates the change of interconnection weights and automatically corrects the interconnection weights. The basic operations of this neural network system, learning and pattern classification, are successfully demonstrated.
Nonlinear spatial filtering can be realised based on some optical effects in light modulating media such as photorefractive, electrooptic or optically non-linear effects. In this report we review the results of our approach to apply the liquid crystal optically addressed spatial light modulators (LCSLM) to spatial filtering. We discuss the properties and features of the optical schemes, where LC SLM is implemented either on the Fourier plane or on the image plane, where it acts as a non-linear filter.
Benzoic acid derivative having vinyl group at the p-position through methylene spacer was synthesized Mixture of the benzoic acidderivative 4,4'-bipyridne (2:1 molar ratio) was found to show a smectic phase in the range of 89℃ to 113℃. Polymerization of the mixture was carried out by using 0.5wt% of 2,2-dimethoxy-2-phenyl-acetophenone as a photoradical imitator. Conversion of the mixture was more than 90% by UV irradiation for 5min at the smectic phase. The smectic phase was maintained after photopolyrrmerization.
A liquid crystalline(LC) monomer showing Sc*, SA and cholesteric phases was synthesized. Polymer networks having ferroelectric liquid crystalline(FLC) structure was obtained by polymerization of the mixtures of the chiral acrylate and LC diacrylate at the Sc* phase. The polymer networks showed an optical switching by application of an electric field.
It is said that the highly ordered structure of liquid crystalline phase (smectic A phase) is similar to that of lipid bilayer. So we would think that the layer structure of liquid crystal is deeply relative to the appearance of biological function. In this study, we synthesized liquid crystalline aliphatic polyesters containing cholesterol moiety in the side chain and examined their thermal properties. The polyester without alkylspacer(m) showed any liquid crystalline phase. However in case of m=2,4,6, the polyesters showed a focalconics texture by polarized optical microscope measurement and were characteristic of smectic A phase.
Carbazole-containing compounds, such as poly-(vinylcarbazole), have considerable interests in their characteristic photoelectric properties. In this work, we have synthesized two types of liquid crystalline copolymers containing carbazole moiety in the side chain in order to clarify the influence on the orientational behavior to the photoelectric properties. Copolymers were prepared by conventional AIBN-initiated free-radical addition-polymerization of methacrylate monomers. Thermal properties of these copolymers were examined by differential scanning calorimetry and thermal optical polarized microseopy, and fluorescent characteristics were also measured.The copolymers exhibited nematic phase above 60mol% of the mesogaenie monomer content. Fluorescent spectroscopy showed that the peak intensity of emissican spectroscopy in the copolymers decreased remarkably after annealing.
Thermal properties of the side chain type liquid crystalline polymer(SLCP)s were deeply influenced by the intermolecular interaction. In order to investigate the effect of hydrogen bonding formed between carboxylic acid groups on thermal properties of the SLCPs, we synthesized the side chain type copolymers containing mesogenic monomer and non-mesogenic monomer with carboxylie acid group. Hydrogen bonding was examined by thermally controlled FT-IR measurements. A mesophase was exhibited for the copolymers containing the mesogenie monomer above 40〜65mol%. The mesophase temperature range(MR) of the copolymers increased in the order of the copolymers with methacrylic acid monomers, with benzoic acid monomers containing a flexible spacer and with benzoic acid monomers. This difference in the MR of the copolymers was demonstrated by FT-IR quantitative analysis of the area of the peak assigned to the dimer structure of the carboxylic acid group.
To develop optically and electrically anisotropic materials, we synthesized poly(thienylene) derivatives with liquid crystalline substituents at the 3-position of thiophene ring. Polythiophene derivatives were synthesized with Ni(0) catalyst, while polythienylenevinylene derivatives were synthesized with Heck reaction following Stille reaction. All polymers showed liquid crystalline phases in cooling process. The oriented film of the polymer exhibited an anisotropic fluorescence.
Polymer networks containing liquid crytalline (LC) molecules were prepared by photopolymerization of LC mixtures containing LC acrylates and E7. The photopolymerization was carried out at a nematic phase and an isotropic phase in a homogeneous glass cell. Composite polymer networks having homogeneously aligned monodomain structure and transparency was obtained by polymerization at the nematic phase, while the composite polymer networks obtained at the isotropic phase showed a polydomain structure resulting in light scattering. The transparency and light scattering behavior were found to control by application of an electric field.Introduction
The microscopic information of the molecule in the liquid crystalline mixture is very interesting , but has not been understood By natural abundance deuterium NMR, we could determine microscopic order of each constitution of the liquid crystalline mixture of 4OCB and 6OCB.
We have used deuterium NMR to investigate the director distribution in a 5CB confined between two glass plates and subject to both magnetic and electric fields. The quadrupolar splitting from a sample with a weak anchoring condition decreases with increasing electric field, through zero and then increases again to a value which is essentially half of that in zero electric field. It would seem that the director orientation changes more or less continuously from being parallel to the magnetic field to being orthogonal to it, as the electric field grows. The voltage dependence of the quadrupolar splitting for a strong anchoring condition is nearly the same as that for a weak anchoring case. However two quadrupolar splittings are observed below a critical value of the electric field.
Deuterium NMR is a powerful technique to investigate the director distribution of a nernatic stab, because the NMR spectrum can contain a simple quadrupolar doublet whose separation us affected by the angle made by the director with the magnetic field vector. Using a contnnuum theory approach we calculated the director distribution in order to understand the experimental results. In this approach the torque balanced equations, involving the magnetic, electric and elastic energy, and a unified surface anchoring energy, was included. The equations with different boundary conditions were numerically solved to obtain the director distributions, which were employed to simulate the NMR spectra. The observed spectra for the strong anchoring condition showed a bistable director distribution below a critical value of the electric field. It was confirmed from the spectral simulations that two director distributions exist in a nematic slab with strong anchoring conditions. One is compatible with the weak anchoring condition, and the other vanishes at the critical point. At higher electrnc fields, for both strong and weak anchoring conditions, the director alignes parallel to the electric field.
Deuterium NMR experiments were carried out for the reentrant liquid crystal CBOBP, (4-cyanobenzoyloxy-[4-octylbenzoyloxy]-.p-phenylene, and the chain-deuterated analog, CBOBP-d17. Significantly different dynamic behaviors were found between the protonated and deuterated alkyl chains. The deuterated chain exhibits distinctly higher orientational order in the reentrant nematic and the smectic A1 phases. A mechanism of the reentrant phase transition is discussed on the basis of the mass effect on the chain dynamics and the phase transition temperatures.
Polarized Raman measurement can determine not only the second but also the fourth order parameters of Raman tensor of local molecular structure in partial oriented system like liquid crystal phase. We have determined the second and the fourth order parameters, P2 and P4 of several homogeneous oriented liquid crystals. Polarized Raman scattering has been measured as a function of the incident laser polarization and the order parameters have been determined by taking account of retardation. This procedure turned out to be more accurate than the previous methods. For 5CB with 50 μm thickness P2 and P4 of ciano group are 0.52 and 0.02, those of phenyl group are 0.52 and 0.12 at 25℃. This result suggests that distributions of phenyl and ciano groups are almost the same and the core part of molecule is rigid. For other liquid crystals the order parameters were determined and ordering of local structures will be also discussed.
We measured the relaxation time of bend distortion in a nematic phase by using light scatterring techniques for various liquid crystal mixtures having phenylene or cyclohexylene group in the core. A cyclohexylene group gives rise to faster relaxation of bend, whereas the relaxation times of twist and splay depend little on the core structure. In addition, the relaxation time of bend mode was twice or three times shorter than that of twist distortion for the cyclohexylene compounds. These results suggest that the responce time of an LCD can be improved by using bend distortion of liquid crystals having a cyclohexan in the core.
The orietational fluctuations in a smectic liquid crystal were successfully observed with a high-speed video camera. From the series of images obtained, first the Fourier transformation of them was made and then the time correlation function at each wave number was calculated. The time correlation function showed an exponential decay and the inverse of the relaxation time was proportional to the square of the wave number, as expected from the continuum theory. This indicates the validity of our experimental method.
We have studied the sponge phase (L3) of binary mixture of C12E5 and water by the dynamic light scattering technique. At the concentration above 2w%, an almost single relaxation related with the cooparative diffusion of membranes is detected. The dynamic correlation lengh is evaluated from the diffusion constant to be a little larger than that obtained for the Lα phase. At the concentration below 2w%, we can find the crossover behavior Γ∝q2 to Γ∝q3 in the dispersion relation between the inverse correlation time Γ and the scattering wavenumber q.
The Gay-Berne potential parameters for model liquid crystalline molecules were determined using the Genetic Algorithm. Parameter optimization was carried out for rodlike beads molecules with axial ratio of 3.0 to 5.6 (consisting of 4 to 8 beads) in 4 typical configurations. The Gay-Berne potential for molecules in parallel and end-to-end configurations can be successfully optimized for any axial ratio. Full optimization including T- and cross-configurations is found to require a further expansion of the Gay-Berne potential itself.
A simple model is introduced to describe phase separations and nematic ordering in solutions and melts of semiflexible polymer chains, taking into account the partial oriecatational ordering of flexible bonds on the chain. We obtain the free energy by combining the Flory-Huggins theory for isotropic solutions and the Maier-Saupe model for describing the coupling between the nematic ordering and straightened bonds. Our theory predicts that the partial stiffening of the fiexible bonds can be a major cause of miscibility gaps showing a bent chimney shape and triple points. We also discuss the extension of chains in a nematic phase.
A simple model is introduced to describe liquid crystal transitions and macroscopic phase separations in binary mixtures of a flexible polymer and a liquid crystal. We examine binodal and spinodal lines on the temperature-concentration plane. We predict the appearance of new phase separations such as the smectic A-nematic, smectic A-isotropic, and smectic A-nematicisotropic phase separations. We also find a tricritical point caused by the interference between liquid crystal transitions and phase separations.
Physical behaviors of systems such as mixtures of liquid crystalline compounds, polymer-liquid crystal complexes, side-chain polymer liquid crystals, interfaces between substrates and liquid crystals, etc...are all not the simple sum of different properties of composed substances but the co-operative phenomena of them each of which is ordered system. From this point of view, we discuss the physical properties of the composite systems, and try to predict them on the basis of molecular statistical mechanics.
We propose a question; " If liquid crystal phase intrinsically possesses characteristics of machinery, then how it behaves? We postulate that liquid crystal phases are mechanical rotor's systems consist of molecular rotors. We have proposed a melting model; A resonance between molecular vibration mode and rotational mode is take place at certain temperature and it induces melting and transition to the existing phase to another phase. We have examined phase transition behaviors as rotor based on mechanical dynamics of rigid and elastic rotors. External and internal damping effects are examined and interpreted in relation to molecular structural characteristics.
Bistable nematic LCD is expected to realize the huge multiplexing of the simple matrix without expensive TFTs. Nematic liquid crystal sandwiched between two substrates homogeneously aligned, shows bistability in case of large twist angle. Static and dynamic spatial distribution of director is calculated by continuum theory. Optical transmittance is calculated by 4×4 matrix method.
In 1995 we proposed a new idea of Homeotropic Splayed Nematic Liquid Crystal Display (HSN-LCD) having excellent time response and viewing angle characteristics. Relations between cell conditions and cell performances are derived from dimensional analyses and numerical simulations. As the result of the above, optimum cell design for HSN-LCD has become possible.
We propose a new idea of Homeotropic π-Twisted Nematic Liquid Crystal Display having steep V-T characteristics required for huge multiplication of the simple matrix without expensive TFT. Relations between cell conditions and cell performances are derived from dimensional analyses and numerical simulations. Experiments correspond well to theoretical predictions.
A new type see-through display using a PDLC(Polymer Dispersed Liquid Crystal) paneland a transparent illuminator constructed by an optical guide plate with a fluorescent lamp has been developed. Foward scattering mode of PDLC was applied to forming process of visual image. Characteristics of haze optically induced in PDLC panel under illumination were investigated. From the results a method of reducing haze level was presented. Illuminant of an image on a display is up to 850cd/m2. Trarnsparency of a see-through display is achieved to 87% / 0.1% (On/off state).
We presented a novel type of orientational photorefractive device, consisting of liquid crystals (LCs) sandwiched with photoconductive polymer films across the insulated polymer films. The photoexcited charges were generated in the photoconductive layers and eventually get trapped in the dark areas at the insulated polymer surfaces. The resulting space charge field reoriented the LC molecules and the holographic gratings were generated. The strong beam coupling effects were observed and the refractive index modulation Δn was estimated to be of the order of 1.1 × 10-3. In addition, we demonstrated the all-optical light modulation using two beam coupling experimental arrangement.
A novel type of orientational photorefractive material based on polymer dispersed liquid crystals (PDLCs) doped with fulleren (C60) was presented. The liquid crystals doped with C60 showed photoconductivity and the holographic grating formation mechanism was originated in the space charge field and resulting reorientation of liquid crystal molecules. The Raman-Nath type of gratings in the PDLCs with a dc applied filod were written by the photorefractive-like space charge field and the large refractive index modulation of the order of 10-3 was obtained. In addition, a stable memory effect of the reorientation was obtained for a 40 wt/60 wt (polymer/liquid crystals) sample.
A novel fabrication method of a LC/polymer grating is proposed. It requires only a simple single-step process by using UV irradiation through a photo-mask. The relief surface grating structure is observed by the scanning electron microscopy(SEM). Electric-field-controlled diffraction effects are also investigated for this LC/polymer grating.
Formation of photoinduced diffraction grating within a thin film of a liquid-crystalline polysiloxane with azobenzene in the side chain was investigated. This polymer exhibited a smtectic C phase between 81 and 87℃, and a nematic phase between 87 and 109℃. Moreover, this polymer formed two kinds of solid state at room temperature: an amorphous state and a crystalline state. The crystalline-state sample was prepared by annealing after heating to the mesophase temperature, and the amorphous-state sample was obtained without heat treatment. The alignment of the mesogenic chromophores in the amorphous state is random, while the they form an interdigitated alignment in the crystalline state. The diffraction light was observed in both states by irradiation of two coherent beams. The diffraction efficiency in the crystalline state was smaller than that in the amorphous state. The diffraction efficiency and the rate of formation of the diffraction grating depend on the alignment of the mesogenic chromophores.
In this study, we used eight types of polyimides (PIs) which were prepared by thermal imidization of poly(amide acid)s as the precursor and evaluated the optical switching behavior of nematic liquid crystals (NLCs; 5CB and ZLI-4751) with the photosensitive PIs as alignment layer. The photosensitive PIs as alignment layer induced the optical switching of NLCs. The optical switching behavior of NLCs was dependent on the structure of PIs. We also found that the optical switching behavior was affected by degree of imidization, light intensity, temperature, and polarity of NLCs. The surface component of the PI shifted from the dispersion component to the polar component, which resulted in decrease of the surface tension between NUC and the PI film due to rubbing. The surface property of PI film was closely related to the optical switching behavior of NLCs.
Polymer liquid crystals (PLCs) with donor-acceptor type azobenzcne moieties (CNAB6) or common azobenzene moieties (AB6) in the side chain were synthesized Homogeneous alignment in the PLCs was induced by using linearly polarized light at 366 nm. Induced order parameter was measured at various irradiation temperaturres by using polarized UV spectroscopy. It was found that the alignment behavior was dependent on the structure of the azobenzene groups. The writing rate of AB6 was higher than that of CNAB6. When the writing light was switched off, discrete increase of the transmittance (positive relaxation) was observed in AB6, while no relaxation in CNAB6. The writing process of CNAB6 can be well dcscibed by a biexponential function. The behavior of azobenzene moieties during the alignment process was investigated. Higher concentration of cis-azobenzene was produced in AB6 during the alignment process. It is one of the reasons for higher writing rate and positive relaxation of AB6.
In-plane alignment control of liquid crystals (LCs) is achieved by linearly-polarized-light (LPL)-treated thin film of polymers having azobenzene side chains. Thin films of p-cyanoazobenzene polymer were irradiated with LPL and absorption dichroism was observed. The dichroic ratio of the polymer thin film was enhanced by heating at 240℃ above Tg of the polymer. The LC alignment on the polymer film was maintained after heating at 100℃ for 1 hour. The thermal stability of LC alignment reflects the stability of dichroism of the polymer film.