Sung-Taek Hur

Liquid crystalline blue phase I observed for a bent-core molecule and its electro-optical performance

We investigated the liquid crystalline blue phase I (BP I) observed for a nematogenic achiral bent-core molecule doped with a small percentage of a chiral additive with a high twisting power. We also observed the electro-optical performance of BP I by incorporating in-plane electric field geometry.

Liquid‐Crystalline Blue Phase Laser with Widely Tunable Wavelength

A lasing peak shift of more than 100 nm is realized due to the large shift of a photonic bandgap of a liquid-crystalline blue phase.

Investigation for correlation between elastic constant and thermal stability of liquid crystalline blue phase I

We investigated the relationship between the elastic constants of host nematic liquid crystals (NLCs) and the thermal stability of their liquid crystalline blue phase I (BPI). By adding bent-core molecules to a conventional NLC, we could gradually increase (decrease) the elastic constant K11 (K33). We confirmed experimentally that the thermal stability of BPI strongly depends on the ratio of the elastic constants K11 and K33 of the host NLCs; the stability increases with decreasing K33/K11 particularly when it is less than unity, being consistent with the theoretical prediction.

Liquid-Crystalline Blue Phase II System Comprising a Bent-Core Molecule with a Wide Stable Temperature Range

A thermodynamically stable blue phase II (BPII) has been prepared, and its electrooptical (EO) performance has been evaluated in a host system of a conventional rodlike nematogen mixed with a bent-core molecule. For the mixed system presented, the widest temperature range of BPII stability, during cooling/heating, was >6 °C. This range is much wider than those of conventional nematogens blended with chiral dopants. EO observations show that the BPII produced exhibited stable EO performance based on the EO Kerr effect. The temperature dependence of the Kerr effect was found to be in approximate agreement with the Landau-de Gennes theory. Furthermore, this material demonstrated very fast, sub-millisecond-scale, response times, thus showing potential for use in high-speed EO devices.

Transition between widened BPs by light irradiation using photo-active bent-core liquid crystal with chiral dopant

Upon UV irradiation of a bent-core liquid crystal (LC) bearing an azo linkage doped with chiral molecules, a photo-induced transition takes place from BPI to BPIII. BPIII is stabilised over 20 °C, while the widening of the BPI range is not so remarkable. The mechanism of photo-induced BPI–BPIII transition is also discussed.

High-transmittance liquid-crystal displays using graphene conducting layers

We report the use of graphene as a highly transparent conductive film in liquid-crystal displays (LCDs). Graphene films were synthesised via chemical vapour deposition, transferred onto glass substrates, and then used to fabricate typical twisted nematic LCD cells. LCD cells using graphene as transparent electrodes exhibited optical transmittances 7.7% higher than LCD cells fabricated using conventional conducting layers based on indium tin oxide (ITO) films. The device characteristics of LCD cells based on graphene electrodes, such as threshold voltage and voltage holding ratio, were comparable to those of conventional LCD cells based on ITO electrodes. These results indicate that graphene is a promising transparent conductive film compared to ITO, yielding LCDs with significantly improved optical transmittance.

A well-aligned simple cubic blue phase for a liquid crystal laser

Here, a well-aligned dye-doped simple cubic blue phase (BPII) sample is fabricated that is stable over the temperature range of 4 °C and has a photonic bandgap (PBG) equivalent to a visible optical wavelength. We demonstrate the maximum widest tunability range of 30 nm as a function of temperature for the well-aligned dye-doped BPII sample. Moreover, it is found that the emission threshold energy for the laser action can be dramatically reduced.

A vertical-field-driven polymer-stabilized blue phase liquid crystal mode to obtain a higher transmittance and lower driving voltage

We demonstrate a vertical-field-driven polymer-stabilized blue phase liquid crystal (PS-BPLC) mode for solving low transmittance and high driving voltage problems in conventional in-plane-switching (IPS) PS-BPLC modes. By controlling the ray directions of incident beams by means of two prism sheets attached to the top and bottom substrates, continuous grayscale properties can be achieved with a vertical field, where the transmittance of the proposed structure can be increased to become twice as high as that of a IPS PS-BPLC cell, and its driving voltage can also be lowered by about 20 V. With the vertical-field-driven PS-BPLC mode, the hysteresis problem of the IPS PS-BPLC mode can also be solved due to a reduction of the electric field required to achieve sufficient field-induced retardation.

23.3: A Vertical-Field-Driven Polymer-Stabilized Blue Phase Liquid Crystal Displays

We demonstrate a polymer-stabilized blue-phase liquid crystal device PS-BPLC, which can be driven by a vertical electric field by transforming normal incident beams into oblique ones. By attaching prism sheets to the cell, the high operating voltage and low transmittance issues on the PS-BPLC employing conventional in-plane field switching modes can be solved simply. The normal brightness can be enhanced by using two prism sheets on top and bottom substrates, respectively.

Temperature-Dependent Behaviours of Blue Phase I Observed for a Bent-Core Molecular System

Temperature-dependent behaviours, such as the Bragg reflection band and the EO performance, of the liquid-crystalline BP I observed for a nematogenic achiral bent-core molecule doped with a small amount of chiral additive was investigated. Our experimental results indicate that the physical behaviours of our sample were highly sensitive to temperature changes.