• Elastomers and Composites
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• v.48 no.2
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• pp.141-147
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• 2013

Polyurethanes containing no mesogenic unit were prepared by polyaddition reaction of homo- and copolyurethanes based on para-type 1,4-phenylene diisocyanate (1,4-PDI), 2,6-bis($\omega$-hydroxypentoxy)naphthalene (BHN5) with 1,4-bis($\omega$-hydroxypentoxy)benzene (BHB5). All copolyurethanes showed monotropic liquid crystallinity, when measurements were performed under shearing. For example, a polyurethane Poly(50/50, mol%) with $[\eta]$=0.32 dL/g exhibited liquid crystallinity in the temperature range from $223^{\circ}C$ to $211^{\circ}C$ in the cooling stage. In contrast, two homopolyurethanes exhibited no explicit mesomorphic behavior, which was observed by DSC (Differental Scanning calorimeter) and measurement and polarized microscopic observation. The mesomorphic behavior of synthesized polyurethane was identified and characterized by differential scanning calorimetry, polarized optical microscope and X-ray.

• Korean Journal of Metals and Materials
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• v.47 no.9
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• pp.542-549
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• 2009

Zr-based amorphous alloy matrix composites reinforced with tantalum continuous fibers were fabricated by the liquid pressing process, and their anisotropic mechanical properties were investigated by tensile and compressive tests of $0^{\circ}$(longitudinal)-, $45^{\circ}$-, and $90^{\circ}$(transverse)-orientation specimens. About 60 vol.% of tantalum fibers were homogeneously distributed inside the amorphous matrix, which contained a small amount of polygonal crystalline particles. The ductility of the tantalum-continuous-fiber-reinforced composite under tensile or compressive loading was dramatically improved over that of the monolithic amorphous alloy, while maintaining high strength. When the fiber direction was not matched with the loading direction, the reduction of the strength and ductility was not serious because of excellent fiber/matrix interfacial strength. Observation of the anisotropic deformation and fracture behavior showed the formation of multiple shear bands, the obstruction of crack propagation by fibers, and the deformation of fibers themselves, thereby resulting in tensile elongation of 3%~4% and compressive elongation of 15%~30%. These results suggest that the liquid pressing process was useful for the development of amorphous matrix composites with excellent ductility and anisotropic mechanical properties.

• Applied Chemistry for Engineering
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• v.21 no.2
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• pp.230-237
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• 2010

A homologous series of linear liquid crystal dimers, ${\alpha},{\omega}$-bis(4-nitroazobenzene-4'-carbonyloxy)alkanes (NATWESn, n = 2~8, 10, the number of methylene units in the spacer) have been synthesized, and the thermal behavior of the series has been investigated. All the dimers formed enantiotropic nematic phases. The nematic-isotropic transition temperatures of the dimers and their entropy variation at the phase transition showed a large odd-even effect as a function of n. This behavior was rationalized in terms of the change in the average shape of the spacer on varing the parity of the spacer. The thermal stability and degree of order in the nematic phase and the magnitude of the odd-even effect of NATWESn were very similar to those of the corresponding ether compounds, while they were significantly different from those of the monomesogenic compounds, 4-{4'-(nitrophenylazo)phenoxy}alkanoyl chlorides and the side-chain liquid-crystalline polymers, the poly[1-{4-(4'-nitrophenylazo) phenoxycarbonylalkanoyloxy}ethylene]s. The results were discussed in terms of the 'irtual trimer model'by Imrie.

• Journal of information and communication convergence engineering
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• v.1 no.3
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• pp.133-138
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• 2003

The preparation of $Al_{2}O_{3}-SiO_{2}$ thin films from less than one micron to several tens of microns in thickness had been prepared from metal alkoxide sols. Two methods, dip-withdrawal and electrophoretic deposition, were employed for thin films and sheets formation. The requirements to be satisfied by the solution for preparing uniform and strong films and by the factors affecting thickness and other properties of the films were examined. For the preparation of thin, continuous $Al_{2}O_{3}-SiO_{2}$ films, therefore, metal-organic-derived precursor solutions contained Si and Al in a chemically polymerized form has been developed and produced in a clear liquid state. In the process of applying to substrates, this liquid left a transparent, continuous film that could be converted to crystalline $Al_{2}O_{3}-SiO_{2}$ upon heating to $1000^{\circ}C$. And, a significant change of the film density took place in the crystallization process, thus leading to the strict requirements as to the film thickness, which could survive crystallization.

• Journal of the Korean Magnetics Society
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• v.12 no.5
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• pp.163-167
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• 2002

In order to study the temperature dependence of the magnetostatic wave modes for an YIG thin film, grown by a liquid phase epitaxy method, The ferromagnetic resonance was performed by an FMR spectrometer in the temperature range -140$\^{C}$∼200$\^{C}$. The magnetostatic surface wave and backward volume wave modes show periodic excitations in parallel configuration. The resonance fields of all modes and intensities decreased with decreasing the temperature. All magnetostatic modes can be well explained by the Walker and Damon-Eshbach theory. The calculated saturation magnetization Ms of the YIG thin film was increased with decreasing the temperature. The line widths of magnetostatic modes changed in various trends with decreasing the temperature.

• Bulletin of the Korean Chemical Society
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• v.28 no.10
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• pp.1651-1655
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• 2007

Rod-like polymerizable LC molecules having two different reactive groups, i.e. acryl and diacetylene groups were prepared. 4-Hydroxyphenyldiacetylenes were synthesized by the coupling reaction of 1-bromoalkynes with 4-ethynylphenol and then reacted with 4-(6-acryloyloxyalkyloxy)benzoic acid to give polymerizable LC molecules 4a-d. The mesomorphic properties of compounds 4a-d were investigated by differential scanning calorimetry, polarized optical microscopy and X-ray diffractometry. Compounds 4a-c exhibited smectic and nematic phases, but compound 4d having a longest alkyl tail among the series formed only a smectic phase. Photopolymerizability of acryl and diacetylene groups was investigated by IR spectroscopy. An anisotropic polymer film could be prepared by selective polymerization of acryl groups with 365 nm UV light in the presence of a photoinitiator (2,2-dimethoxy-2-phenylacetophenone). The subsequent reaction of diacetylene groups with 254 nm UV light disrupted the anisotropic structure, suggesting that these LC molecules could be used for imaging on the film.

• Journal of the Korean Wood Science and Technology
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• v.48 no.3
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• pp.405-413
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• 2020

Recycling of ionic liquid (1-ethyl-3-methylimidazolium acetate, [EMIM]Ac) after the pretreatment of Salix gracilistyla Miq. was conducted and the effect of the recycling number on the enzymatic saccharification yield was investigated. Enzymatic saccharification was performed using an enzyme cocktail (Acremonium cellulase and Optimash BG) at 50 ℃ for 72 h. All recycled [EMIM]Ac samples showed a lower amount of water soluble fraction than pure [EMIM]Ac. On increasing the recycling number from 1 to 4, the amount of water soluble fraction decreased from 18% to 15%. The X-ray diffraction pattern of the products pretreated with recycled [EMIM]Ac showed cellulose I crystalline polymorph. The crystallinity of the product pretreated with recycled [EMIM]Ac was 47-49%, which was lower than 33% of that with pure [EMIM]Ac. The yields of glucose and xylose decreased in the pretreatment with recycled [EMIM]Ac compared to that with pure [EMIM]Ac.

• Journal of the Korean Institute of Telematics and Electronics
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• v.10 no.3
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• pp.10-22
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• 1973

Recently, nematic and nematic-cholesteric mixtures of substances have been discovered which have stimulated progress in electronics research and industry. In the liquid crystalline state, compounds with nematic mesopheses possess the ability to scatter light, depending on the strength of an applied electric field. The rewaking of interest in this fascinating but long-neglected area has occasioned the introduction of the subjects at the situation of the chemists. Since 1888 year, approximately 2000 compounds have been found to possess the unusual properties of what are commonly referred to as liquid crystals. In this paper, a comprehensive review will not be attempthed here. Nevertheless, some general information necessary to familarize the reader with rather exotic field will facilitate an understanding of the new effect and its application.

• Carbon letters
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• v.13 no.4
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• pp.191-204
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• 2012

Carbon nanotubes (CNTs) have exceptional mechanical, electrical, and thermal properties compared with those of commercialized high-performance fibers. For use in the form of fabrics that can maintain such properties, individual CNTs should be held together in fibers or made into yarns twisted out of the fibers. Typical methods that are used for such purposes include (a) surfactant-based coagulation spinning, which injects a polymeric binder between CNTs to form fibers; (b) liquid-crystalline spinning, which uses the nature of CNTs to form liquid crystals under certain conditions; (c) direct spinning, which can produce CNT fibers or yarns at the same time as synthesis by introducing a carbon source into a vertical furnace; and (d) forest spinning, which draws and twists CNTs grown vertically on a substrate. However, it is difficult for those CNT fibers to express the excellent properties of individual CNTs as they are. As solutions to this problem, post-treatment processes are under development for improving the production process of CNT fibers or enhancing their properties. This paper discusses the recent methods of fabricating CNT fibers and examines some post-treatment processes for property enhancement and their applications.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.957-962
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• 2003

The preparation of $Al_2$O$_3$-SiO$_2$ thin films from less than one micron to several tens of microns in thickness had been prepared from metal alkoxide sols. Two methods, dip-withdrawal and electrophoretic deposition, were employed for thin films and sheets formation. The requirements to be satisfied by the solution for preparing uniform and strong films and by the factors affecting thickness and other properties of the films were examined. for the preparation of thin, continuous $Al_2$O$_3$-SiO$_2$ films, therefore, metal-organic-derived precursor solutions contained Si and Al in a chemically polymerized form has been developed and produced in a clear liquid state. In the process of applying to substrates, this liquid left a transparent, continuous film that could be converted to crystalline $Al_2$O$_3$-SiO$_2$ upon heating to 100$0^{\circ}C$. And, a significant change of the film density took place in the crystallization process, thus leading to the strict requirements as to the film thickness, which could survive crystallization.