Kazuaki Tarumi

Advanced liquid crystals for television

This review summarizes the diverse material requirements of the main Liquid Crystal Display (LCD) technologies used for televisions (TVs). We discuss recent advances in liquid crystal materials for this application. We highlight key materials and discuss synthesis, structure–property relations and LC mixture properties. For all technologies we have achieved fast switching LC mixtures (16 ms) and are en route to 8 ms thus improving the switching times for the next generation of superior performance LCD TVs.

The TV in Your Pocket: Development of Liquid‐Crystal Materials for the New Millennium

New liquid crystals with very low viscosity, good mesophase behavior, and high reliability are necessary to achieve the breakthrough from flat computer monitors to large displays for television. Fluorine plays a decisive role not only because of the polarity it induces in organic molecules but also because of its low polarizability and weak propensity for ion solvation. In addition, subtle stereoelectronic effects in fluorine-containing liquid crystals influence material properties and allow these to be tuned to some extent to achieve the desired outcome. Some fairly sophisticated chemistry is required that is normally ruled out in the specialty chemicals industry because of cost. The television display market is now entering a phase of saturation. The broad availability of the internet has led to an ever increasing tendency for mobile products. Tablet PCs and smartphones require touch-panel functionality and low power consumption. New LCD modes with high-performance liquid crystals and additional components, such as polymerizable materials, can be used in such products.

Effects of Electric Double Layer and Space Charge Polarization by Plural Kinds of Ions on Complex Dielectric Constant of Liquid Crystal Materials

The complex dielectric constant of a liquid crystal material, 4-cyano-4-alkyl-biphenyl (5CB), was measured in low-frequency regions below 1000 Hz. The anomalous increasing behavior was analyzed using an equivalent circuit which takes two kinds of contributions into account: one is from the electric double layer and the other is from the space charge polarization. It was found by numerical calculations that these two effects exhibit different dependences of dielectric dispersion on the thickness of a specimen, and both effects were successfully distinguished in the experimental results. In the analysis of the space charge polarization, the experimental results were best fitted by the calculated results with five kinds of ions in terms of the diffusion coefficient. These measurements can be applied to a precise determination of the attributes of plural kinds of ions, such as the diffusion coefficient and the number density.

Liquid Crystals Based on Hypervalent Sulfur Fluorides: Pentafluorosulfuranyl as Polar Terminal Group

The somewhat “exotic” pentafluorosulfuranyl functionality is one of the strongest electron-withdrawing groups with a purely inductive effect. Owing to its chemical stability and the resulting high dipole moment of its aromatic derivatives, this group was crucial to the design and synthesis of a new class of highly polar liquid crystals (such as 1) for application in active matrix displays. A computational model was developed with the aim to understand and predict the electrooptic properties of liquid crystals based on hypervalent sulfur fluorides.

NOVEL CHARACTERIZATION METHOD OF IONS IN LIQUID CRYSTAL MATERIALS BY COMPLEX DIELECTRIC CONSTANT MEASUREMENTS

The frequency dependence of the complex dielectric constant of liquid crystal materials doped with tetra-n-butylammonium iodide (TBAI) is investigated in the low-frequency region, and the experimental results are analyzed in terms of space charge polarization. The contribution from an electric double layer is also taken into consideration in the analysis. By means of curve fitting utilizing theoretical expressions of the space charge polarization, five sets of diffusion coefficient and density values are obtained for mobile ions. It is confirmed by experiments on the temperature dependence that five kinds of ions follow Waldens rule, and verified from the viewpoint of ion radii that two of the five kinds of ions are TBA+ and I-. The frequency-dependent dielectric properties, which are characteristic of the behaviors of ions, can be well explained by this study and the analytical method introduced here is considered to be powerful for the evaluation of the attributes of mobile ions.

A NOVEL TYPE OF LIQUID CRYSTALS BASED ON AXIALLY FLUORINATED CYCLOHEXANE UNITS

Decidedly higher clearing temperatures and often also broader mesophases are exhibited by axially fluorinated cyclohexane derivatives 1 and 2 relative to their nonfluorinated analogues. A convenient method for the multigram synthesis of 1 and 2, which represent a promising new type of liquid crystals with positive or negative dielectric anisotropy, is presented.

Calculation of Optical and Dielectric Anisotropy of Nematic Liquid Crystals

The optical birefringence (Δn) and dielectric anisotropy (Δe) of nematic liquid crystals were calculated using the well-known theories of Vuks and Maier-Meier, respectively. The molecular dipole moments and polarizabilities needed for the estimation were taken from semiempirical AM1 calculations. The calculated values are in good agreement with the experimental results for the investigated compounds having different core structures and polar substituents.

Dynamic Behaviour of Twisted Nematic Liquid Crystals

Expressions describing the dynamic behaviour in terms of τon and τoff for twisted nematic structures have been derived through rigorous analysis. The obtained equations are discussed separately for the twisted nematic (TN) and super twisted nematic (STN) cases. Experimentally obtained switching times under various boundary conditions validate the approach. We discuss the results from the liquid crystal substance developers point of view.

Model of Ion Solvation in Liquid Crystal Cells

The leading display technology, active matrix display requires very high reliability. Characteristic parameters for high reliability are, for instance, voltage holding ratio and residual DC values. Both parameters show a strong deterioration if some charge carrier or contamination is present in active matrix display cells, and this leads to an inacceptable contrast value of the display. The physicochemical understanding of such contamination causes, origin or solvation, still remain unclear. A model is presented in this paper, using a simple simulation method called `sparkle whose results are in very good agreement with the experimental results.

Optimization of liquid crystals for television

Abstract— LCD TVs have dramatically improved in performance during the last 2 years. At the same time, the sale prices decreased by more than 50%. Together with the introduction of digital terrestrial broadcasting, this resulted in increasing sales of LCD TVs. This paper gives an overview of the main liquid-crystal display (LCD) technologies used for TVs. We discuss key materials, synthesis, structural property relationships, and the optimization of LC mixture properties. For all technologies, we have achieved fast-switching LC mixtures (16 msec). Novel materials for LC mixtures for the next generation of superior performance LCD TVs with 8-msec switching times are shown.