Jeong-Yeon Hwang

Vertically aligned liquid crystals on a γ-Al2O3 alignment film using ion-beam irradiation

Using ion-beam (IB) irradiation, liquid crystals (LCs) were vertically aligned (VA) on a γ-Al2O3 alignment film. Atomic-layer deposition was used to orient the LCs on high-quality γ-Al2O3 alignment films. The LC molecule orientation indicates the vertical direction of the atomic-layer-deposited γ-Al2O3 alignment films. X-ray photoelectron spectroscopy showed that IB irradiation changed the chemical structure, shifting the Al–O binding energy and altering the Al–O bonding intensity. The low-voltage transmittance characteristics of the VA LC displays on the γ-Al2O3 alignment films were also measured, showing reduced voltage and power requirements.

Low-power operation of vertically aligned liquid-crystal system via anatase-TiO 2 nanoparticle dispersion

Electro-optic performance of a liquid-crystal (LC) system is enhanced by TiO(2) nanoparticle dispersed in nematic liquid crystal (NLC). The 2.5 V threshold voltage of LC for device operation is lowered to 0.5 V through TiO(2) nanoparticle mixing up to 2 wt.%. To characterize the shape and size distribution of the nanoparticles, high-resolution transmission electron microscopy is employed. Transmittance spectra for the TiO(2) dispersed LC structure and nondispersed LC structure showed that transparency of the TiO(2) dispersed LC is similar to that of pure liquid LC.

Therapeutic potential of panduratin A, LKB1-dependent AMP-activated protein kinase stimulator, with activation of PPARα/δ for the treatment of obesity

Aim: AMP‐activated protein kinase (AMPK) activators have shown potential as therapeutic agents for metabolic disorders. This study was conducted to evaluate therapeutic potential of panduratin (PAN) A, a natural AMPK stimulator, with activation of PPARα/δ for the treatment of obesity.

Titanium dioxide surface modification via ion-beam bombardment for vertical alignment of nematic liquid crystal

We introduce the characteristics of the titanium dioxide (TiO(2)) inorganic film deposited by rf magnetron sputtering for liquid crystal display applications. The TiO(2) films demonstrated vertical alignment (VA) of the liquid crystals (LCs) obtained by using ion-beam (IB) bombardment. As observed by using x-ray photoelectron spectroscopy, the chemical structure of the TiO(2) was changed by IB bombardment, altering the Ti-O bonding of the Ti 2p spectra to lower intensity levels. Breaking Ti-O bonding by IB bombardment created pretilt angles between the TiO(2) film and LC molecules. The better voltage-transmittance characteristics of the VA LCDs based on TiO(2) film were measured and compared with the same characteristics of polyimide film.

A chemically modulated polystyrene surface for homogeneously aligned liquid crystals using various ion beam exposure angles

In this study, transparent polystyrene (PS) was replaced with conventional polyimide material. As a non-contact process, an ion beam (IB) bombardment process was applied to align the homogeneous liquid crystal (LC) material on the PS surfaces. Confirming the atomic force microscopy and X-ray photoelectron spectroscopy analysis, the chemical compositional changes of the IB-irradiated PS surfaces were determined as a function of the IB exposure angle although there was no effect of modulation of the physical geographic characteristics on IB-irradiated PS surfaces. Using this analysis, the optimal IB bombardment condition was determined at the IB exposure angle of 45°. Finally, the electro-optical properties of an LC cell suggest the use of PS in conventional LC alignment materials.

Control of High Pretilt Angle for Nematic Liquid Crystal on Homeotropic Alignment Layer by In-situ Photoalignment Method

Pretilt angle generation and liquid crystal (LC) aligning capabilities for a nematic (N) LC with obliquely polarized UV exposure on a homeotropic polyimide (PI) surface by an in-situ photoalignment method were studied. The high pretilt angle of 30θ for NLC with obliquely polarized UV exposure on the PI surface for 20 min can be achieved. The pretilt angle generated in NLC by the in-situ photoalignment method was higher than that generated by a conventional photoalignment method on a homeotropic alignment layer. Also, we suggest that the generation of pretilt angle in NLC with obliquely polarized UV exposure during imidization of the polymer for homeotropic alignment is a promising method to generate a high pretilt angle. Lastly, the good electro-optical (EO) characteristics of the photoaligned vertical alignment (VA)-liquid crystal display (LCD) by UV exposure on the PI surface for 10 min were observed.

Liquid Crystal Alignment Effects Using a-C:H Thin Films Deposited at RF Bias Condition

The nematic liquid crystal (NLC) aligning capabilities using a-C:H thin film deposited at the three kinds of rf bias condition were investigated. A high pretilt angle of about 11° by the ion beam alignment method was observed on the a-C:H thin film (polymer-like carbon) deposited at 1 W rf bias condition, and the low pretilt angle the NLC than 1 W rf bias conditions was observed on the a-C:H thin film (diamond-like carbon) deposited at rf 30 W and 60 W bias condition. Consequently, the high LC pretilt angle and the good aligning capabilities of LC alignment by the ion beam alignment method on the a-C:H thin film deposited at 1 W rf bisa condition can be achieved. Also, the good thermal stability of LC alignment by the IB alignment method on the a-C:H thin film as working gas at rf bias condition can be achieved.

Alignment Characteristics of Liquid Crystal Molecules on Titanium Dioxide Thin Film

We present the characteristics of titanium dioxide (TiO2) inorganic film deposited by RF magnetron sputtering for liquid crystal display applications in this paper. TiO2 films supported vertically aligned liquid crystal (LC) molecules based on ion-beam (IB) irradiation time dependence. Uniform alignment was obtained only when the incident time was two minutes with 1.8 keV of incident energy and an incident angle of 45°. Energy from uniform high-density plasma by IB irradiation affected the interaction between the TiO2 layer and LC molecules to produce vertical alignment of the LC molecules.

Continuous Pretilt Angle Controlled No-Bias-Bend Pi Cell via Blended Polyimide Liquid Crystal System

The controllable pre-tilt angle of liquid crystals was investigated using a blend of horizontal and vertical polyimide prepared using a rubbing method. Various pretilt angles ranging from 0° to 90° were achieved as a function of the vertical polyimide content. We observed uniform liquid crystal alignment on the rubbing-treated blended polyimide layer. A no-bias-bend (NBB) pi cell with an intermediate pretilt angle of 47.8° was manufactured. This cell had no initial bias voltage and a low threshold voltage, which indicates that it has low power consumption. In addition, the response time of the NBB pi cell was rapid.

Surface oxidation and charge transfer inducing dipole–dipole interactions for homogeneous liquid crystal orientation

Generally, liquid crystal (LC) orientation on rubbed polystyrene (PS) surfaces runs in the direction orthogonal to the rubbing process. In this study, homogeneous LC orientations were produced in the direction parallel to the ion beam (IB) process on PS surfaces using various IB exposure energies. Through x-ray photoelectron spectroscopy it was shown that IB irradiation resulted in the reformation of O=C bonds resulting from surface oxidation or charge transfer, reversely tracing out the produced pretilt angles of the homogeneous LC. Moreover, thermal tests on IB-irradiated PS surfaces were carried out which showed that a relatively high IB exposure energy induced a thermally stable LC alignment property. Finally, we determined the mechanism by which homogeneous LCs are aligned on IB-irradiated PS surfaces with electro-optical properties of twisted-nematic LC cells.