• 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.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.69-74
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• 2017

In this study, cholesteryl 4-n-alkoxybenzoates (Chol-n), with alkyl groups used for controlling the temperature of transition to the liquid crystal phase, were synthesized, and the effects of the length of the alkyl groups on the physical properties of the liquid crystal compounds were investigated. The chemical structures and thermal and liquid crystalline properties of the synthesized compounds were investigated by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy ($^1H$-NMR), differential scanning calorimetry (DSC), and polarizing optical microscopy (POM). The synthesized compounds showed melting transition temperatures ($T_m$) in the range of $103^{\circ}C$ to $143^{\circ}C$ and all of the compounds except Chol-6 exhibited a wide liquid crystal phase temperature range of about $60^{\circ}C$ to $100^{\circ}C$. No correlation between the number of carbon atoms in the molecule and the thermal properties of the compounds was found. All of the synthesized compounds showed an enantiotropic cholesteric phase, which was accompanied by a chiral smectic phase in the compounds Chol-6, Chol-8, Chol-9, and Chol-10. All of the compounds exhibited thermochromism in the liquid crystal state, and their color changed from red to blue as the temperature was increased.

• Korean Journal of Crystallography
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• v.3 no.2
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• pp.111-119
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• 1992

Alexandrite crystals were grown by the Czochralski method. Relationships between or ystal quality and crystal growth factors such as pulling rate, rotation rate, purity of BeO po wders and evaporation loss compensation of BeO and Cr3+/Al3+substitution ratio were investigated. As a result, 1) high purity (more than 99.99p,) of BeO, as a raw material, is requisite condition for single crystal growth, 2) evaporation loss comp ensation is also requisite for high quality crystal growth. This compensation depends on pulling rate and Cr3+/Al3+ ratio. And 3) optimum pulling and rotation rate for alexandrite growth were 0.5∼1.0mm/hr and 20∼25rpm, respectively. Ale xandrite crystals were grown to (001) direction. Various types of defects were detected by the polarizing microscope and we discussed how to remove these defects. And room tempo rature absorption and fluorescence spectra were measured.

• Korean Journal of Optics and Photonics
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• v.21 no.5
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• pp.185-189
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• 2010

We demonstrate a single-frequency wavelength tunable erbium-doped fiber (EDF) ring laser. We used an unpumped-EDF as a saturable-absorber in order to obtain a stable single-frequency with a narrow-linewidth single-polarization mode in the ring cavity. The lasing wavelength was controlled by using bending-induced strain, such as tension and compression strain corresponding to the bending direction, applied to the fiber gratings. The fiber laser exhibited an output power of -1.85 dBm at a wavelength of 1540.72 nm for a pumping power of ~400 mW. An extinction ratio was measured to be more than 60 dB. The proposed tunable fiber laser maintains nearly the same output power while its lasing wavelength is controlled over in a wavelength range of 5 nm.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.10
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• pp.4041-4046
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• 2010

Wholly aromatic polyesters having flexible alkoxy side chain were synthesized by direct polycondensation. The synthetic polymers have been characterized by $^1H$-NMR, FT-IR. DSC, TGA, optical polarizing microscope and X-ray diffractometer. The inherent viscosities (${\eta}_{inh}$) measured in 1,1,2,2-tetrachloroethane (TCE) were 0.46~2.41 dL/g. The polymers having side chain showed double melting transition, ie, solid-sanidic liquid crystalline (LC) phase transition ($T_{m1}$) and sanidic LC phase-nematic LC phase transition ($T_{m2}$). As incresing length of alkoxy side chain, phase transition temperatures decreased and solubilities in organic solvents incresed. The peaks of $2{\theta}\;{\simeq}5$ and $2{\theta}\;{\simeq}20$ in X-ray diffractograms are due to crystallization of polymer main chain and of long side chain, respectively.

• Journal of the Korean Chemical Society
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• v.26 no.3
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• pp.188-193
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• 1982

Four new thermotropic copolyesters were prepared and their liquid crystal properties were investigated by differential scanning calorimetry and on a hot-stage of a polarizing microscope. Three copolyesters had same mesogenic unit, triad aromatic ester structure, interconnected through a random combination of either odd-even, or odd-odd, or even-even number of methylene groups in the polymethylene flexible spacers. Another random copolyester consisted of mesogenic units of 1 : 1 mixture of central methyl-and bromohydroquinone moieties with two flanking p-oxybenzoate units connected by decamethylene spacer. All of the polyesters formed nematic liquid crystal phase upon melting. The transitions for melting and nematic ${\to}$ isotropic transformations could be reversibly observed by DSC as well as by microscopic study. The thermodynamic properties for their liquid crystal ${\to}$ isotropic phase transitions were discussed in relation to their chemical structures.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.274-275
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• 2000

광결정(photonic crystal)으로 광원의 자발 방출을 조절하면 문턱전류 없는 레이저, 고효율 다이오드, 파장 크기에서 손실 없이 급격히 꺾을 수 있는 광도파로 등 기존의 광소자에서 얻을 수 없는 좋은 성능을 얻을 수 있을 것으로 예상된다. 이러한 광결정은 유전체를 파장정도 크기에서 주기적으로 배치시킨 인공적인 결정인데 고체에서 원자의 주기적인 배치로 전자가 전파할 수 없는 진동수 영역, 즉 밴드갭이 생기는 것과 유사하게 빛에 대해서 빛이 전파할 수 없는 진동수 영역인 광밴드갭(photonic bandgap)을 가진다. 그런데 관심있는 광영역에서 3차원 모든 방향으로 광밴드갭이 있는 구조물은 마이크로미터보다 작은 내부 구조를 가지는 복잡한 3차원 구조물로 제작이 어렵다. 이러한 어려움을 극복하기 위해 제작이 비교적 용이한 3차원 광밴드갭 구조물이 찾아지고 있다. 다른 접근 방법으로 평면(x-y)에서는 2차원 광밴드갭을 이용하고 제 3의 방향(z축)으로는 전반사를 이용하는 구조는 제작이 용이할 뿐만 아니라 처음부터 광원의 편광을 TE 또는 TM 모드로만 방출 되도록 준비해 줄 수 있으면 거의 3차원 광결정에서 얻을 수 있는 효과를 낼 수 있는 것으로 발표되었다.$^{(1)}$ 이 방법을 이용하여 최근에 미국의 캘리포니아 공과대학(Caltech)을 중심으로 레이저 동작을 보여 주었다.$^{(2.3)}$ 공기로 둘러싸인 얇은 유전체 평판에서 생기는 전반사와 평판 위에 2차원 삼각형살창(triangular lattice)에 구멍을 뚫어 얻는 2차원 광밴드갭을 이용해 3차원 공진모드를 형성하였다. 이러한 구조에서 1개만 구멍을 매워서 만든 공진기는 저온(143 K)에서 레이저 발진을 보였고 여러 개의 구멍을 매운 경우는 상온에서 펌프 펄스의 유지시간이 0.5% 인 경우 레이저가 동작하는 것을 보여주었다. 이는 구조내에서 열전도가 문제가 된다는 것을 의미하는데 위아래가 공기로 둘러 싸여 있어 발생한 열이 가는 유전체 네트웍을 통해서만 전달 될 수 있기 때문이다. (중략)

• Polymer(Korea)
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• v.30 no.5
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• pp.417-421
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• 2006

Photo -alignment of poly (siloxane cinnamate) (PSCN) was studied to better understand the alignment mechanism of cynnamoyl groups under various process conditions. DSC and polarized microscope studies showed that the isotropic temperature oi PSCN was about $105^{\circ}C$ and the liquid crystallinity, once formed, did not completely disappear even when the temperature went into the isotropic regions. UV/Vis absorption study suggested that the photo - dimerization was the main photo alignment mechanism and it's efficiency could be enhanced through the self-alignment of PSCN. It was also found that photo-dimerization was in competition with photo-fries reaction and the photo- alignment of PSCN was interfered with the excessive UV because of the strong photo-fries reaction. However, photo - fries reaction could be suppressed by adjusting the UV wavelength.

• Elastomers and Composites
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• v.44 no.4
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• pp.436-441
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• 2009

Semi flexible polyesters containing aromatic rings and pentamethylene groups in the main chain were synthesized by direct polycondensation reaction. The structures of these polymers were investigated by $^1H$-NMR and FT-IR and the phase transition behavior was characterized with DSC, TGA and crossed polarizing microscope. Inherent viscosities ($\eta_{inh}$) of polymers measured in phenol/p-chlorophenol/1,1,2,2-tetrachloroethane were between 0.46 and 1.30 dL/g. As increasing the linearlity of rigid moieties in polyster, melting transition temperatures ($T_m$) increased and solubilities in organic solvents decreased. P-H, P-mH and P-4H of the polymers formed turbid melts that showed stir-opalescence and nematic phase at the broad anisotropic region, However, P-R, P-C and P-2B did not exhibit any textures related to the liquid crystallinity.

• Journal of Korea Society of Industrial Information Systems
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• v.13 no.1
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• pp.11-21
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• 2008

Recently, it has shown an increased interest in 3D stereoscopic contents due to the development of the digital image media. Therefore, many techniques in 3D stereoscopic image generation have being researched and developed. However, it is difficult to generate high immersion and natural 3D stereoscopic contents, because the lack of 3D geometric information imposes restrictions in 2D image. In addition, control of the camera interval and rendering of the both eyes must be repetitively accomplished for the stereo effect being high. Therefore, we propose integrated editing system for 3D stereoscopic contents production using a variety of images. Then we generate 3D model from projective geometric information in single 2D image using image-based modeling method. And we offer real-time interactive 3D stereoscopic preview function for determining high immersion 3D stereo view. And then we generate intuitively 3D stereoscopic contents of high-quality through a stereoscopic LCD monitor and a polarizing filter glasses.