• Polymer(Korea)
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• v.24 no.3
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• pp.399-406
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• 2000

A thermotropic liquid crystalline polymer (TLCP) containing a flexible spacer was synthesized from hydroquinone, p-hydrofybenzoic acid, and 1,6-dibromohexane. Intercalation of TLCP in layered clays is accomplished by heating the polymer with dodecyl ammonium-montmorillonite (C$_{12}$-MMT) above melt transition temperature (T$_{m}$). Liquid crystallinity of the TLCP/C$_{12}$-MMT hybrid was not observed when $C_{12}$-MMT content was above 1 wt%. Some of the $C_{12}$-MMTs in TLCP were highly dispersed in a nanometer scale, but some of them were agglomerated. Thermal and morphological properties of the nanocomposites were examined by differential scanning calorimetry (DSC), thermogravimetric analyzer (TGA), polarized optical microscope, and electron microscopes (SEM and TEM). TEM).

• Composites Research
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• v.16 no.4
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• pp.44-50
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• 2003

The damage zone around a crack tip occurring before the fracture is a significant domain. which affects the toughening mechanism of materials. In this study. the growth process of damage zone in the vicinity of crack tip for rubber-modified epoxy resin is investigated using an acoustic emission(AE) analysis. The weight fractions of rubber(CTBN 1300$\times$B) in rubber-modified epoxy resin are 5 wt% and 15 wt%. The fracture toughness($K_{IC}$) and the fracture energy($G_{IC}$) were measured using 3 point bending single-edge notched specimens. The damage zone and rubber particles distributed around the crack tip were observed by a polarized optical microscope and an atomic force microscope(AFM). The damage zone around crack tip of rubber-modified epoxy resin was formed at 13 % loading and developed until 57 % loading of the fracture load. The crack initiated at 57 % loading grew repeatedly in the stick-slip propagation behavior. Based on time-frequency analysis, it was confirmed that AE signals with frequency bands of 0.15~0.20 MHz and 0.20~0.30 MHz were generated from cavitation and stable/unstable cracking inside the damage zone.

• Journal of the Korean Chemical Society
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• v.46 no.2
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• pp.125-138
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• 2002

The kiln at Chollanamdo Kwangjusi Ch'unghyodong, which produced punch'ong and white wares for a period of 70 to 80 years in the 15th century, is examined for their scientific technological param-eters. Punch'ong sherds were divided into seven different groups according to the location and the layer of the waste mounds from which they were excavated. Optical and scanning electron microscope were used for microstructural observations and X-ray diffraction and polarized microscope for mineral characteristics. For determining the firing temperature, sherds were refired at different temperatures and their micro-structural changes were observed. Some wares such as the group CHE2 was high quality wares fired at high emperature around 1200$^{\circ}C$ for palace use, but as the ceramics ware became more widely used and the white wares increasingly preferred over punch'ong, lower quality wares of rougher raw materials were firedat lower temperatures around 1100-1150$^{\circ}C$ in quantity. They used local raw materials of several types, all available locally.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.4039-4045
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• 2014

The crystallization behavior of irradiated polypropylene (PP) and the blend is an important parameter for polymer processing. Blends of PP/low density polyethylene (LDPE) with different LDPE contents were prepared by melt mixing in a twin screw extruder. The effect of the LDPE content on the irradiation effectiveness of the PP/LDPE blend with trimethylolpropane-trimetacrylate (TMPTMA) as a crosslinking co-agent was investigated in conjunction with the LDPE loading in the blend. The non-isothermal crystallization and crystal structure were measured by DSC, X-ray diffraction (XRD), and polarized optical microscopy (POM). A decrease in the melting temperature of PP was observed due to irradiation, which may be due to the PP chain scissioning effect of irradiation. The Ozawa component n represents a rod shaped, disc shaped and sphere-shaped geometry of the crystal if the value corresponds to 2, 3 and 4, respectively. Based on Ozawa analysis, the values of n were 3.8 and 2.3 for the pure PP and PP blends with 30 wt% LDPE, respectively. The fact that the crystal geometry of PP changed from spherical to disc and rod shaped was confirmed by Ozawa analysis and POM. The ${\beta}$ form XRD peak of the PP/LDPE blend at $16.1^{\circ}$ disappeared after irradiation due to the crosslinking reaction.

• The korean journal of orthodontics
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• v.27 no.6 s.65
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• pp.979-995
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• 1997

The purpose of this study was to identify the preventive and the progressive inhibitory effects of enamel demineralization with fluoride releasing light-and self-cured orthodontic sealants(FluoroBond), in vitro, under the polarizing light microscope and the scanning electon microscope. The polarizing light microscopic group was subdivided into seven groups(Group A-Group G). The scanning electron microscopic group was also subdivided into seven groups(Group A'-Goup G'). For polarizing light microscopic evaluation, longitudinal sections were made longitudinally by Maruto cutter(Maruto Co., Japan) and Maruto grinding machine(Maruto Co., Japan). Sections were examined and photographed by the polarizing light microscope(Olympus Optical Co., Japan) using crossed polars and with the enamel rod longitudinal axis oriented at $45^{\circ}$ to the extinction position. For scanning electron microscopic evaluation, the specimens were coated with a highly conducting layer of gold palladium in a model Hus-4 high-vacuum evaporator and examined in an ISI-100B scanning electron microcope operated at 20kV. The results of this study were as follows : 1. The mean depths of artificial carious lesions under a polarized light microscope were $Group\;A(5.08{\mu}m),\;Group\;B(47.82{\mu}m,\;Group\;C(8.42{\mu}m),\;Group\;D(7.20{\mu}m),\;Group\;E(85.41{\mu}m),\;Group\;F(60.38{\mu}m),\;Group\;G(60.13{\mu}m)$. 2. There were statistically significant differences in Group B compared with Group A, C, and D(p<0.05), and also, in Group I compared with Group F and Group G(p<0.05). 3. Light-and self-cured orthodontic sealants had the preventive effects of enamel demineralization. 4. Light-and self-cured orthodontic sealants had the progressive inhibitory effects of enamel demineralization. 5. The time progress of demineralizing agent had no influence on the samples of light-and self-cured orthodontic sealants under the scanning electron microscope. 6. There was no difference between the specimens of light-and self-cured orthodontic sealants both in the polarized light microscopic group and in the scanning electron microscopic group.

• Journal of the Korean Wood Science and Technology
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• v.36 no.6
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• pp.96-104
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• 2008

In this study, the observation of test pieces with an optical microscope was carried out after fabricating 4 groups of standard lacquer, in order to inquire into the ancient lacquering techniques. Group I had transparent reddish brown color, and the part of layer was indefinite, and the layer polished was easily distinguished. Group II had mostly transparent yellowish brown color, and it was possibility distinguished the layers when they were varnished with mixed lacquer after prime coating, and when they were varnished with lacquer as the prime coating. Group III set up membrane in the hardening process of the lacquer, and the lacquer and the unsaturated fatty acid of internal part was dried, so the top layer and the lacquer layer were separated and observed. Group IV: When the lacquer coat film of Group IV test pieces were observed in polarized light, the ferrous components were seen as the black and red color were mixed, and the silica crystals of silty soil were distinguished by reflection of lights. And the colors were distinguished as the lacquer layer of ruddle had red color, and the mixed lacquer of reddish lacquer and ruddle had the deep red color at the top and the bottom, but the middle part had the bright red color.

• Applied Chemistry for Engineering
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• v.9 no.1
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• pp.71-75
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• 1998

Liquid crystalline compounds with amine terminal group and related linear and cross-linked liquid crystal polymers with epoxy resin structure were synthesized and characterized to develope matrix materials for polymer dispersed liquid display applications. Both linear and crosslinked side chain type liquid crystal polymers made with aromatic amine mesogens and ethylene glycol diglycidyl ether exhibited nematic texture as shown by polarized optical microscope(POM) and their transition temperatures were determined both by DSC and POM. Liquid crystal polymer samples also showed even-odd effect as the spacer length of aromatic amine mesogens were varied, however, the effect was samller than that of low molecular weight mesogens. Changes of nematic-to-isotropic transition($T_{NI}$) of crosslinked type polymer liquid crystals were also disscussed in relation to the concentration change of crosslinking agent 1,10-diaminodecane.

• Applied Chemistry for Engineering
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• v.9 no.1
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• pp.66-70
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• 1998

Several liquid crystalline monomers were synthesized and characterized to utilize as new matrix materials of liquid crystal/polymer composite films for display application. Liquid crystalline compounds which have azo group as center link, cyano group at one of the terminal position in common and bromoalkyl(azo(n)), azidoalkyl(AZI(n)), aminoalkyl(ALC(n)) as the terminal group were synthesized and identified respectively by FT-lR, $^1H-NMR$ spectrometer and elemental analysis. All these compounds exhibited nematic liquid crystalline region in the certain temperature range as determined by DSC and polarized optical microscope. These liquid crystalline compounds also showed a typical even-odd effect in both $T_{KN}$ and $T_{NI}$ due to conformational change as the length of terminal alkyl chain, $-(CH_2)n-$. was varied.

• Journal of the Korean Ceramic Society
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• v.46 no.4
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• pp.419-424
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• 2009

Congruent or stoichiometric $LiNbO_3$ fiber single crystals were grown by the $\mu$-PD method, and the grown fiber crystals have the several (2 or 3) ridges with a diameter of $1.35{\sim}1.5\;mm$ and a length of $40{\sim}100\;mm$. In this $\mu$-PD process, different growth rates ($10{\sim}60\;mm/h$) were applied. Pt wire or $LiNbO_3$ crystal was used as a seed. The properties of grown $LiNbO_3$ fiber single crystals having a-axis or c-axis according to seeds were effected by the grown conditions(Pt tube diameter, pulling speed, after heater etc.). Disk-type $LiNbO_3$ samples were poled in condition of DC 5 V/cm at 1050, 1075 or $1100^{\circ}C$. XRD, SEM, conoscope image through the polarized microscope, $T_C$ measuring apparatus, optical transmittance measuring instrument are used to identify the properties of $LiNbO_3$.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.4
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• pp.421-430
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• 2016

To prepare mesophase pitches through low energy process, pyrolysis fuel oil with $AlCl_3$ has been modified using two-step heat treatment which is heat-treated at $330^{\circ}C$ for 3~5 h after pre-treatment at $250^{\circ}C$. The result of polarized optical microscope observation, mesophase is not observed in pitches carried out only pre-heat treatment. While mesophase content is significantly increased from 9% to 100% according to increasing secondary heat treatment time from 3 h to 5 h. Synthesizing of the mesophase pitch at low temperature of $330^{\circ}C$ is attributed to decrease of viscosity of the pitches carried out first heat treatment with $AlCl_3$. The result of Fourier-transform infrared spectroscopic analysis, it is expected that aromatization of aliphatic compounds is dominant at early secondary heat treatment, on the other hand, polycondensation reaction becomes dominant as secondary heat treatment time increases. Aromaticity and stacking height of the pitches secondary heat treated for 5 hours are more increased about 25% and 107%, respectively, than that of pitches carried out only first heat treatment.