Shin-ichi Yamamoto

39.1: Invited Paper: Optically Isotropic Nano-Structured Liquid Crystal Composites for Display Applications

In this paper, we present the phase behavior and electro-optical Kerr effect of the optically isotropic liquid crystal composites, which require no surface treatment for device fabrication. Anomalously large Kerr constant, more than 10−8 mV−2 and fast response, less than sub-milli-second were observed at a room temperature.

A large Kerr constant polymer-stabilized blue phase liquid crystal

A polymer-stabilized blue phase liquid crystal (BPLC) composite with a large Kerr constant (K∼13.7u2002nm/V2) is developed and its electro-optic properties characterized. In addition to the reduced operating voltage, this BPLC also exhibits a fast response time (∼1u2002ms), high contrast ratio (>1000:1), and relatively small hysteresis (<6%). It will undoubtedly accelerate the emergence of BPLC for next-generation display and photonic devices.

A low voltage and submillisecond-response polymer-stabilized blue phase liquid crystal

We report a polymer-stabilized blue phase liquid crystal (BPLC) whose Kerr constant is about 2.2× larger than previous record. When filled in a 3.2-μm-thick vertical field switching cell, the on-state voltage is merely 8.4u2009V (at λu2009=u2009514u2009nm) while keeping submillisecond response time and negligible hysteresis (<1%) at the room temperature. These results imply that the dawn of BPLC era for high speed display and photonic devices has finally arrived.

Optically isotropic-nanostructured liquid crystal composite with high Kerr constant

The relationship between material parameters of host nematic liquid crystals (LCs) and Kerr constant of their nanostructured chiral LC composites was investigated. We made certain that the Kerr constant of nanostrutured chiral LC composites was closely related to the parameters of their host LCs, such as value of the difference of refractive index (Δn), the dielectric anisotropy (Δe), and bend to splay elastic constant ratio (K33∕K11).

Optimized blue-phase liquid crystal for field-sequential-color displays

We report an optimized blue phase liquid crystal (BPLC) mixture JC-BP08 for field-sequential-color (FSC) display applications. JC-BP08 exhibits several attractive features: 1) its fast average gray-to-gray response time enables FSC display, which in turn triples the resolution density and optical efficiency. 2) Its voltage holding ratio is >99.4% at 25°C and >93.2% at 60°C. 3) Its average dielectric constant e’≈87 is still manageable by the bootstrapping driving to enable 240 Hz operation. 4) Using a triangular protrusion electrode structure, the transmittance can reach 74% at 15V, which enables single-TFT driving. 5) With two-domain structure, it offers indistinguishable gamma shift and wide viewing angle. We proposed a voltage charging model and found a linear relationship between the required charging time and e’, which is validated by our experimental results.

Optically isotropic liquid crystal composite incorporating in-plane electric field geometry

We demonstrate an intriguing liquid crystal display (LCD) mode that comprises an optically isotropic LC composite incorporating in-plane electric field geometry. No surface treatment, such as rubbing, is required to fabricate the LCD mode because it is based on an isotropic state. The measured response time is of submillisecond order. This rapid response originates from the local reorientation of molecules in small LC clusters as well as from strong polymer stabilization. The LCD mode has several unique features such as fast response, continuous greyscale capability and a high contrast ratio.

Fast electro-optic device controlled by dielectric response of planarly aligned cholesteric liquid crystals

Planarly aligned cholesteric liquid crystals of short pitch were applied by the in-plane electric field. The reorientation of the director, increasing pitch, and flexoelectricity induce the change of transmission. The main effect in this research is due to the director reorientation along the electric field. The flexoelectricity deters the change in the birefringence induced by the dielectric response. The response was very fast for the effectively thin periodic boundary of the half-pitch of liquid crystal. The contrast ratio was more than 80 for red light and the response time was less than 0.1 ms for the experimental conditions.

Troponoid metallomesogens with 5-alkoxy, 5-alkoxycarbonyl, 5-alkanoyloxy, 5-alkyl, 5-alkoxy-2-amino, and 5-alkoxy-2-alkylamino substituents

Metal complexes (Cu, VO, Zn, Mn, and Ni) with 5-alkoxy-, 5-alkoxycarbonyl-, 5-alkanoyloxy-, and 5-alkyl-tropolonato structures as well as bis(5-alkoxy-2-aminotroponato)copper were synthesized. All bistropolonato Cu complexes showed ordered smectic phases such as hexatic smectic B, smectic G(J), and smectic H phases. The Zn, Mn, and Ni complexes were non-mesomorphic whereas the VO complexes with 5-alkoxy- and 5-alkanoyloxy-tropolonato groups had mesophases. Among the Cu complexes, bis(5-alkanoyloxytropolonato)copper complex had the highest clearing point. The mesomorphic properties depend on the kinds of substituents, metal ions, and heteroatoms of the core. The Cu complexes have a square planar coordination structure and the VO complexes a square pyramidal one. The thermal stability of the Cu complexes was explained by the size and symmetry of the core structure. To decrease the transition temperatures of bis(5-alkoxytropolonato)copper complexes, secondary alkoxyl groups were introduced at the C-5 positions and the two oxygen atoms of the bistropolonato core were replaced by two nitrogen atoms, which reduced the symmetry of the structure.

Polarization Analysis of Nanostructured Chiral LC Composites

The polarization analyses of the isotropic nanostructured LC composites, which is a promising candidate of next-generation LCD material, were performed to investigate the residual birefringence after application of an electric field. The composites showed negative, positive and nearly zero in azimuth angle of optical rotation for the chiral nematic phase, the induced isotropic phase and the isotropic phase, respectively. When the residual birefringence occurred, the optical rotatory of the isotropic nanostructured LC composites exhibited slightly negative. It is suggested that the primary cause of the residual birefringence is the electric field-induced phase transition to the chiral nematic phase.

17.1: Invited Paper: Optically Isotropic Liquid Crystals for Electro-optical Devices

Optically isotropic liquid crystals show quick response, and enable rubbing free process in LCD fabrication. However there are some specific issues to be solved for mass production. In this paper, the relations between electro-optical properties and preparation condition and the other properties of relatively recent materials are mainly shown.