Effects of Nematic Compounds with High Clearing Points on the Multiplexing Performance of Twisted Nematic Displays

The addition of nematic compounds with high clearing points (N_h) to multiplexable nematic liquid crystals decreases the temperature dependence of the threshold voltage of twisted nematic displays. This effect depends on the dielectric anisotropy of the nematic liquid crystals containing N_h, as well as on the increase in T _c. In the case of 4-n-butylphenyl 4'-(4”-butyibenzoyloxy) benzoate, the low threshold voltage was exceptionally compatible with a small temperature dependence of threshold voltage, and this result was attributed to the large temperature dependence of the dielectric anisotropy in comparison with that of nematic liquid crystals containing other N_h's.     

Optics of Twisted Nematic Liquid Crystal Layers

Calculations have been made of the optical properties of various liquid crystal displays (LCDs) based on twisted nematic liquid crystal layers. It is shown that the steepness of the electro-optical characteristics of TN LCDs can be reduced and consequently the gray-scale capability can be improved by decreasing the twist angle. The twist reduction permits the realization of displays which, due to their outstanding gray-scale capability and low inherent coloration, are particularly suited for active matrix TV-applications. In addition to calculations made on displays based on weakly twisted layers, a comparison is made of the optical properties of displays with a high multiplex capability, which utilize highly twisted nematic liquid crystal layers. It is shown that the brightness of the OMI LCD can be improved without deterioration of the weak inherent coloration. This renders OMI LCDs particularly well suited for applications as time-multiplexed, full colour, high information content panels.     

Order Parameter and the Performance of Nematic Guest-Host Displays

A simple model of a nematic guest-host display is presented in which the limiting “on” and “off” states are considered to be uniform arrays of molecules oriented perpendicular and parallel (or at a small tilt angle), respectively, to the plane of the display. Calculated contrast ratio and brightness curves are presented for several angles of view and of all planes of view as functions of dye order parameter, pretilt andploarizer efficiency. The effects of host refractive index and front surface reflectivity are discussed.     

Assessment of Nematic Guest-Host Systems for Application to Integrated Liquid Crystal Displays

An optimized configuration of the nematic guest-host effect is described in which a 90° twist cell is used. In order to assess the suitability of nematic guest-host systems for use in integrated displays in which a significant dc voltage may appear across the liquid crystal, several dye/host systems were tested with up to 1.5V dc superimposed on the normal 5V r.m.s. drive signal. Degradation was monitored by measurement of tilt, clearing point and absorbance. One system tested showed no significant degradation after 9 × 10³ hr. Excellent correlation was observed between stability of a dye/host system in a driven display and the reversibility of the reduction of the dye in acetonitrile solution at a platinum electrode.     

The Electro-Optical Properties of Doping Polycyclic Aromatic Hydrocarbon Liquids in Twisted Nematic Liquid Crystals

In this paper, doping liquid materials to enhance the electro-optical (EO) properties of twisted nematic liquid crystals (NLCs) was presented. Two polycyclic aromatic hydrocarbon (PAH) liquids, toluene and 1-methylnaphthalene, were chosen as dopants in order to lower the driving voltage and response time of the NLCs. We find that the main reason of this phenomenon is due to a large amount of reduction in the rotational viscosity of PAH liquids doped NLCs. Without the drawbacks of aggregation that the solid nanoparticles could have, the method of doping liquids provides a more reliable choice for applications in various LC display systems.     

Infrared Linear Dichroism of Nematic Solutions I. Orientation of Guest Molecules in Nematic Hosts

The orientational order and the biaxiality of some mono-substituted benzenes in namatic liquid crystals have been determined from infrared linear dichroism measurements. The experimental results are in good agreement with the theoretical predictions of the mean field theory.     

Market Trends for Flat Panel Displays

Abstract

Arecent report from Stanford Resources entitled ‘Flat Panel Monitor Market Trends 1988’ presents a realistic forecast for the FPD market, which is expected to reach a shipment value of $4 billion in the year 2000. The Flat Panel Display market covers active matrix twisted nematic displays (TFT-LCD) and matrix-addressed super-twisted nematic displays (STN-LCD), and the following are highlights from the market analysis and forecasts.     

Nematic Thiophenes for STN-LCDS and Flexoelectric LCDS

Abstract

We report anew class of liquid crystals incorporating a 2,5-disubstituted thiophene ring and one or two conjugated trans-carbon-carbon double bonds in the terminal chain for use as components of nematic mixtures for TN-LCDs and STN-LCDs. The combination of these molecular elements contribute towards generating a high birefringence, a high nematic clearing point as well as a low viscosity for these materials. Several of these compounds exhibit a melting point below room temperature. This is the first time a room temperature nematic phase has been reported for phenyl thiophene derivatives. The new thiophene compounds can be used to induce a high birefringence in nematic mixtures for LCDs with short response times.     

Highly Birefringent Nematic Liquid Crystals for Reflective STN Applications

Abstract

An important parameter of any LCD containing portable electronic device is a low power requirement. The reflective STN display mode offers a moderate to high information content display with low power consumption. One method to realise colour in this mode is to use a large retardation (dΔn) value in the cell. For a cell gap of 6 μm, and a retardation of ?1.5, a birefringence (Δn) of greater than +0.2 is necessary. To achieve such a value in an STN LC mixture, materials with broad nematic range, good solubility and a Δn value of <+0.25 are required.

A study of the trans-cyclohexyldifluorophenyltolane core structure was made and a large number of dialkyl, alkenyl-alkyl and alkoxy materials were synthesised and characterised. These materials possess low to moderate melting points, broad purely nematic mesophases, a high Δn and very good solubility in nematic LC hosts. They are suitable materials for inclusion in mixtures for colour reflective STN displays.     

Dielectric and Electrooptic Investigations in the Nematic Phase of 5-n-Pentyl-2-[4-n-nonyloxyphenyl]-1,3-dioxane

The dielectric constant and the dielectric loss of 5-n-pentyl-2-[4-n-nonyloxyphenyl]-1,3-dioxane were investigated in the region of 0.1 to 10 MHz. An isotropy temperature was detected, at which the static dielectric anisotropy Δε₀₁ = 0. Using both the Freedericksz and the DAP effect, we measured the frequency dependence of the threshold voltage U₀ and compared the results with those of the dielectric measurements. In the case of DAP effect we could find two different types of dispersions curves of U₀.     

Measurements of dc Kerr Constants for a Homologous Series of Nematic Compounds

The dc Kerr constants of seven p,p′-n-alkoxyazoxybenzene homologous compounds have been measured as functions of temperature in the isotropic phase. The observed pretransitional behavior near the isotropic-nematic transition is consistent with the phenomenological model of Landau-de Gennes with the Onsager's loal-field correction included in the dielectric tensor. The dc polarizability anisotropy and the average orientation of the permanent dipole with respect to the long molecular axis are deduced from the experimental results. Their variations with increase of methylene groups in the alkyl chains are discussed.     

Dielectric Behaviour of the Nematic Phase of 4-n-Pentyloxyphenyl 4-(3-Bromo-4-n-nonyloxybenzoyloxy)-3-ethyl-benzoate (PBNEB)

Due to the high viscosity of 4-n-pentyloxyphenyl 4-(3-bromo-4-n-nonyloxybenzoyloxy)-3-ethyl-benzoate (PBNEB) the dielectric reorientation processes take place in the kHz and MHz range respectively. We observed two different relaxation ranges in the nematic phase from 10 Hz to 10 MHz if the measuring field is parallel to the director and one relaxation range for the perpendicular orientation. Dielectric measurements at 6.7 GHz demonstrate that at this frequency ϵ′∥ and ϵ′⊥ can be regarded as high-frequency limit. The experimental values are discussed from the point of view of the Meier-Maier theory.     

Experimental Evidence for a Hyperscaling Relation at a Nematic to Smectic A Phase Transition

A hyperscaling relation v_″ + 2v_┴ = 2 – α is examined for the nematic to smectic A transition of 4-octyloxy-4′-cyanobiphenyl (8OCB) and 4-octyl-4′-cyanobiphenyl (8CB). From the heat capacity results, 2-α is analyzed to be 1.84 ± 0.03 for 8OCB and 1.75 ± 0.02 for 8OCB. On the other hand v_″ + 2v_┴ is calculated from the results reported by X-ray experiments to be 1.87 ± 0.12 for 8OCB and 1.69 ± 0.11 for 8CB. From the above coincidences the hyperscaling relation is found to be applicable to the nematic to smectic A transition.     

A Novel Method for Study of a Smectic Phase Obtained from a Strongly-Deformed Nematic Texture

A simple method for the growth of conventional or reentrant smectic phases from strongly-deformed conventional or reentrant nematics, is proposed. It permits the formation of surface-induced and surface-governed conventional and/or reentrant smectic textures which can be studied from the scientific point of view or can be applied in the laser-addressed thermo-optic smectic liquid crystal storage displays for the creation of static figures. The simple method proposed might be applied for study of many smectics arrising either from conventional or reentrant nematic phases under cooling or heating.     

Preparation of a Carbon Nanotube-Reinforced UV/Heat Dual-Curable Adhesive for Liquid Crystal Displays

Abstract

There is strong demand for narrow-bezel liquid crystal displays (LCDs) in the display industry. Adhesive materials for narrow-bezel LCDs require excellent adhesive properties in order to provide the same level of adhesive strength as conventional sealants, even when applied in small amounts. In this study, we prepared a previously unknown, highly adhesive, carbon nanotube-reinforced (CNT-reinforced) UV/heat dual-curable adhesive for narrow-bezel LCDs. Single-walled and multi-walled CNTs (SWCNTs and MWCNTs) were employed as fillers, resulting in superior adhesive properties; in particular, the inclusion of SWCNTs improved both adhesion and resistance to water permeability compared to a conventional adhesive.     

Silver (I) coordination by 1-(t-butyl)-2-benzoylaziridine

The reaction between AgNO₃ and 1-(t-butyl)-2-benzoylaziridine (tBBA) leads to the formation of bis-(1-(t-butyl)-2-benzoylaziridine) nitrato silver (I) which is a new metal aziridine derivative. The crystal structure was established by X-ray diffraction. [Ag(tBBA)₂(NO₃)] crystallizes in space groupC222₁ witha=11.877(6),b=13.560(4),c=16.923(4)Å andZ=4. The silver atom is six-coordinated by two N atoms of two aziridine rings (Ag-N=2.39(1)Å), two O atoms of two benzoyl groups (Ag-O=2.60(1)Å) and two O atoms of the nitrato group (Ag-O=2,60(1) Å). The coordination around the silver atom defines a very distorted octahedron with the C2 symmetry. The twofold axis passes through one O and the N nitrato atoms, and the silver atom. The nitrato group and tBBA act as bidentate ligands. These results are in contrast with our previous studies on aziridine zinc (II) complexation where the zinc atom is not coordinated by the benzoyl group.     

Measurement of Flexo-coefficients for Nematic LCs without the Influence of the Impurity Ions by Using the Chromatographic Isolation Method

The sum of the flexo-coefficients (e₁₁+e₃₃) was measured by the capacitance characteristic depending on the applied dc voltage in the HAN cell. The voltage for the minimum value of the capacitance was shifted by the influence of flexoelectric effect. One of the important problems for the evaluation for the flexo effect was the influence of impurity ions. Then, the chromatographic isolation phenomenon was used to separate impurity ions when the LC material was injected into the empty cell by the capillary action. The coefficient (e₁₁+e₃₃) of ZLI-4792 was measured, and a value of 26.0 pC/m was obtained.     

Computer Modelling of the Light Propagation through the Complex Anisotropy Systems - the way of a Determination of the Optical Parameters of the Liquid Crystal Displays

A mathematical and numerical method for an analysis of a liquid crystal displays (LCD) has been presented. The assumptions of the calculations of a light propagation through the display are shown. The real conditions of a work of these displays have been taken into account. Basing of this mathematical model a computer program for a numerical modelling of the optical parameters of LC displays working in real conditions has been worked out. This program makes possible to obtain the most important parameters of a display such as: contrast ratio, luminance in on- and off-state, spectral characteristics of light and its colour coordinates in these both states. The results obtained from this program have been verified experimentally. Very high conformity of these results has been obtained.