• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.469-472
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• 2003

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 $11^{\circ}$ by the ion beam alignment method was observed on the a-C:H thin film (polymer-like carbon) deposited at 1W rf bias condition, and the low pretilt angle of the NLC was observed on the a-C:H thin film(diamond-like carbon) deposited at rf 30W and 60W bias condition. Consequently, the high NLC pretilt angle and the good aligning capabilities of LC alignment by the IB alignment method on the a-C:H thin film deposited at 1W rf bisa condition can be achieved.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.67-70
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• 2003

The control of tilt angle for nematic liquid crystal (NLC) with negative and positive dielectric anisotropy on the rubbed homeotropic polyimide (PI) using baking method by hot plate equipment was investigated. LC tilt angle decreased with increasing baking temperature and time. Especially, the low LC tilt angle of positive type NLC ($\Delta\varepsilon$ >0) on the rubbed homeotropic PI surface by increasing temperature and time was measured. The tilt angle of positive type NLC ($\Delta\varepsilon$ >0) is smaller than that of the negative type ($\Delta\varepsilon$ >0) on rubbed PI with increasing baking temperature and time. We consider that the tilt angle of NLC is decreased due to increasing the steric interaction between horizon component of permittivity $\varepsilon$ = of NLC and the stress of polymer side chain by high temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.05a
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• pp.100-103
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• 2005

Homogeneously aligned nematic liquid crystal modes are representatively the -FFS (fringe-field switching) mode using liquid crystal (-LC) with negative dielectric anisotropy, the +FFS mode and the IPS (in-plane switching) mode using +LC with positive dielectric anisotropy. In view of image quality evaluation standard of LCD, we compared characteristics of the brightness, the contrast ratio (CR) and color shift when the modes have respectively optimized phase retardation values $(d{\Delta}n)$. Consequently, in the most sensitively viewing angle of a man's physical vision, both FFS modes have advantage over the IPS mode from the brightness & the CR point of view. We are also confirmed that the +FFS mode out of them shows the smallest color shift according to all viewing directions in grey levels.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.86-92
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• 2019

Polymers with various compositions of azobenzene and hexamethylene groups in the main chain were synthesized by a Schotten-Baumann reaction and their properties were investigated. The chemical structures and physical properties of the synthesized polymers were investigated by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, differential scanning calorimetry, thermogravimetric analysis, polarized optical microscopy, and x-ray diffraction. The polymers showed an inherent viscosity of 1.28-1.36 dl/g and were relatively insoluble in most organic solvents. The melt transition temperature increased rapidly with increasing number of azobenzene groups in the polymer. When the azobenzene monomer content was more than 50 mol%, no melting transition occurred below the decomposition temperature. Among the polymers with a melt transition temperature, the MP-A3C7 and MP-A5C5 polymers were liquid crystalline materials and exhibited a nematic phase with weak liquid crystallinity over a wide liquid crystal temperature range. This difference in the properties of the synthesized polymers is likely due to the changes in intermolecular forces resulting from the linearity and polarity of the trans-form of azobenzene.

• Polymer(Korea)
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• v.32 no.5
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• pp.446-457
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• 2008

Three kinds of hydroxypropyl cellulose (HPC) derivatives: 6- (cholesteryloxycarbonyl) pentoxypropyl celluloses(CHPCs) with degree of esterification(DE) ranging from 0.6 to 3, 6-[4-{4'-(nitrophenylazo)phenoxycarbonyl}] pentoxypropyl celluloses (NHPCs) with DE ranging from 0.4 to 3, and fully 6-(cholesteryloxycarbonyl) pentanoated NHPCs (CNHPCs) were synthesized, and their thermotropic liquid crystalline properties were investigated. All the CHPCs and NHPCs with $DE{\leq}1.7$ formed enantiotropic cholesteric phases, whereas CNHPCs with 6-(cholesteryloxycarbonyl) pentanoyl DE(DEC) more than 1.6 exhibited monotropic cholesteric phases. On the other hand, NHPCs with $DE{\geq}2.4$ and CNHPCs with $DEC{\leq}1.3$ showed monotropic nematic phases. NHPCs with $DE{\leq}l$, as well as HPC, formed right-handed helices whose optical pitches (${{\lambda}_m}'s$) increase with temperature, while all the CHPCs formed left-handed helices whose ${{\lambda}_m}'s$ decrease with temperature. In contrast with these derivatives, NHPCs with $1.4{\leq}DE{\leq}1.7$ and CNHPCs with $DEC{\geq}1.6$ did not display reflection colors over the full cholesteric range, suggesting that the helical twisting power of the cellulose chain and the cholesteryl group highly depends on the chemical structure and DE of mesogenic group.

• Journal of Adhesion and Interface
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• v.25 no.1
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• pp.169-274
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• 2024

Recent attention has been drawn to materials that undergo reversible expansion and contraction in response to external stimuli, leading to morphological changes. These materials hold potential applications in various fields including soft robotics, sensors, and artificial muscles. In this study, a novel material capable of responding to high temperatures for protection or encapsulation is proposed. To achieve this, liquid crystal elastomer (LCE) with nematic-isotropic transition properties and polyimide (PI) with high mechanical strength and thermal stability were utilized. To utilize a solution process, a dope solution was synthesized and introduced into micro-printing techniques to develop a two-dimensional pattern of LCE/PI bilayer structures with sub-millimeter widths. The honeycomb-patterned LCE/PI bilayer mesh combined the mechanical strength of PI with the high-temperature contraction behavior of LCE, and selective printing of LCE facilitated deformation in desired directions at high temperatures. Consequently, the functionality of selectively and reversibly encapsulating specific high-temperature materials was achieved. This study suggests potential applications in various actuator fields where functionalities can be implemented across different temperature ranges without the need for electrical energy input, contingent upon molecular changes in LCE.

• Polymer(Korea)
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• v.36 no.6
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• pp.776-788
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• 2012

Octa[8-{4-(4'-cyanophenylazo)phenoxy}]octyl and octa[8-{4-(4'-cyanophenylazo)phenoxycarbonyl}]heptanoated disaccharide derivatives were synthesized by reacting cellobiose, maltose, and lactose with 1-{4-(4'-cyanophenylazo) phenoxy}octylbromide or 1-{4-(4'-cyanophenylazo)phenoxycarbonyl}]heptanoyl chloride, and their thermotropic liquid crystalline and photochemical phase transition behavior were investigated. All the {(cyanophenylazo)phenoxy} octyl disaccharide ethers (CADETs) formed monotropic nematic (N) phases, whereas all the {(cyanophenylazo) phenoxycarbonyl}heptanoated disaccharide esters (CADESs) exhibited enantiotropic N phases. Compared with CADETs, CADESs showed higher isotropic (I)-to-N phase transition temperatures. Photoirradiation of the disaccharide derivatives in a glass cell or in a cell with a rubbed polyimide (PI) alignment layer at a N phase resulted in disappearance of the N phase due to trans-cis photoisomerization of azobenzene, and the initial N phase was recovered when the irradiated sample was kept in the dark because of cis-trans thermal isomerization and reorientation of trans-azobenzenes. The rates of the photochemical N-I and the thermal I-N phase transition of disaccharide derivatives in a cell with a rubbed PI alignment layer were faster than those in a glass cell, and were significantly different from those observed for the monomesogenic compounds containing cyanoazobenzene and the 4-{4'-(cyanophenylazo)phenoxy}octyl glucose and cellulose ethers. The results were discussed in terms of difference in cooperative motion of azobenzene groups due to the flexibility of the main chain, the number of mesogenic units per repeating units, and the distance between the azobenzene groups.