• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2000.07a
• /
• pp.303-307
• /
• 2000

The crystal structure of ZnS fabricated by gas-liquid phase reaction was obtained by XRD and refined by RIETAN near R$_{wp}$ factor 10%. The increasement of HCP phase depended on extra H$_2$S gas and the lattice parameter and crystalline size changed by the relative ratio of multiphase. Using ZnS of the different multiphase ratio and crystalline size, sintered ZnS:Cu, Al green phosphor and the CL property resulted optimum luminescence in the range of 91~94% and 150~190$\AA$, respectably, FCC/HCP ratio and crystalline size. As changing of structure ratio, the reason of different luminescence property is now studying. As well as, after XRD pattern of TiO$_2$powder fitted by RIETAN and the structure factor using MEED method simulated about each atom of (002) plane. Additionally, we proposed RIETAN and MEED were the methods of the study of luminescence mechanism for many phosphor materials.s.

• Composites Research
• /
• v.30 no.1
• /
• pp.1-6
• /
• 2017

Epoxy resin (EP) is one of the most famous thermoset materials. In general, because EP has three-dimensional random network, it possesses thermal properties like a typical heat insulator. Recently, there has been increasing interest in controlling the network structure for making new functionality from EP. Indeed, the new modified EP represented as liquid crystalline epoxy (LCE) is spotlighted as an enabling technology for producing novel functionalities, which cannot be obtained from the conventional EPs, by replacing the random network structure to oriented one. In this paper, we review current progress in the field of LCEs and their application for the highly thermal conductive composite materials.

• Korean Journal of Materials Research
• /
• v.8 no.8
• /
• pp.678-684
• /
• 1998

By means of constant- pressure molecular dynamics simulations, we studied the liquid- glass- crystalline transition of a system composed of Lennard- Jones particles with periodic boundary conditions. Atomic volume and enthalpy were calculated as functions of temperature during heating and cooling processes. The Wendt- Abraham ratio derived from radial distribution function and the angular distribution function characterizing short range order were analyzed to distinguish between liquid, glass and crystalline states. A liquid phase resulting from a slow heating of an initial fee crystal amorphized on fast quench, but it crystallized on slow quench. When slowly heated, the amorphous phase from fast quench crystallized into an fee structure. A system with free surface was shown to melt from the surface inward at a lower temperature than bulk system and to have a strong tendency for crystallization even during a fast quench from a liquid state.

• Proceedings of the Korean Society of Dyers and Finishers Conference
• /
• 2012.03a
• /
• pp.51-51
• /
• 2012

Cellulose is extremely difficult to dissolve cellulose in water and most common organic solvents due to their stiff molecular structure, close chain packing and intermolecular hydrogen bonds. Recently, cellulose solutions using ionic liquids (ILs) as a green solvent have been known to form cholesteric liquid crystalline phase at high cellulose concentration. In this study, the phase transition and rheological behaviors of concentrated cellulose/[AMIM]Cl solution were investigated using polarized optical microscopy and rheometry. Studies were conducted to characterize the influence of cellulose concentration on the phase transition of the cellulose solution and the mechanical properties of the regenerated fibers spun from the anisotropic cellulose/[AMIM]Cl solutions.

• Proceedings of the Korean Fiber Society Conference
• /
• 1998.10a
• /
• pp.94-97
• /
• 1998

We have been studying :he synthesis of thermotropic polyurethanes, based on structural modifications by means of (i) the introduction of bulky substituent group in the aromatic ring to decrease the degree of lateral packing, (ii) the copolymerization of two kinds of monomers having different alkylene lengths to lower the regularity of the polymer structure, and (iii) the use of nonlinear monomers to lower the persistence length of the polymer chain in the liquid crystalline phase and to decrease the lateral interactions in the solid state. (omitted)

• Textile Coloration and Finishing
• /
• v.15 no.4
• /
• pp.73-79
• /
• 2003

It is generally known that cotton treated with liquid ammonia has better soft handle, wrinkle recoveries and stability of appearance as compared with the alkali mercerized cotton. In this study, the various cotton fabrics treated with liquid ammonia$(NH_3)$, sodium hydroxide(NaOH) and sodium hydroxide(NaOH)/liquid ammonia$(NH_3)$ and untreated cotton fabric were investigated and compared in terms of physical properties and dyeing behavior. As the result, the strength of four kinds of cotton fabrics were similar. But the elongation of cotton treated with liquid ammonia increased slightly. Liquid ammonia treatment reduced the crystallinity of cotton and the crystalline structure of cotton transformed from cellulose 1 to mixed structure of celluloseIand III. In dyeing, dyeing rate decreased but equilibrium dye uptake increased by liquid ammonia treatment of cotton fabrics.

• Bulletin of the Korean Chemical Society
• /
• v.33 no.5
• /
• pp.1647-1652
• /
• 2012

With the objective to design and synthesis of Schiff's base symmetrical liquid crystal dimmers and to study the effect of molecular structure variation ($o-ortho$, $m-meta$, $p-para$) and change in alkoxy terminal chain length on mesomorphic properties of liquid crystals, We have synthesized Schiff base dimers from dialdehyde derivative containing 2-hydroxy-1,3-dioxypropylene as short spacer with aniline derivatives having different lengths of terminal alkoxy chains ($n$ = 5, 7, 9). The chemical structure of the final products was characterized by proton nuclear magnetic resonance ($^1H$ NMR) spectroscopy and fourier transform infrared (FT-IR) spectroscopy. The mesomorphic properties and optical textures of the resultant dimers were characterized by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The existence of smectic A phase transition was confirmed by the observation of batonnets and fan shaped textures in optical microscopy when compound were heated from crystalline phase. All of the dimers of this series, with the exception of $\mathbf{2S_5}$ -ortho, -meta, -para, were thermotropic liquid crystal. The compound $\mathbf{2S_9}$ -meta was monotropic, while the rest were enantiotropic. It was found that the change in terminal alkoxy chain length has pronounced effect on the mesomorphic properties. The temperature range of smectic A phase window widens with increasing alkoxy chain length.

• Journal of Adhesion and Interface
• /
• v.15 no.4
• /
• pp.161-168
• /
• 2014

New self-assembled discotic liquid crystals have been prepared through single hydrogen bonding between phenol and pyridine moieties, and their liquid crystalline properties were investigated. For the construction of discotic structure, we used phloroglucinol as a core molecule and trans-4-alkoxy-4'-stilbazoles with systematically varied alkyl chain lengths as peripheral units. FTIR results showed that the intermolecular hydrogen bonds between core and peripheral molecules are successfully formed, and the stability of the hydrogen bond is strongly influenced by molecular ordering. Discotic complexes exhibited different liquid crystalline phases depending on the length of alkyl chains around the discotic mesogen. The discotic complexes with longer alkyl chains showed hexagonal columnar mesophases, while the other complexes formed nematic columnar mesophases. These results indicated that the type of mesophase structure was strongly dependent on the alkyl chain length around the aromatic core.

• Bulletin of the Korean Chemical Society
• /
• v.28 no.1
• /
• pp.108-114
• /
• 2007

The lyotropic behaviors to form the structure of distearoylphosphatidylcholine (DSPC)-based liquid crystal (LC) hydrated by only propylene glycol (PG) without water were examined by differential scanning calorimetry (DSC), X-ray diffractions (XRD), polarized microscope (PM) and transmission electron microscope (TEM). By increasing the amount of PG instead of water, it showed the phase transition to be gradually changed from anisotropic structures to other structures more close to isotropic ones and their appearance to be changed from solid-like states to liquid-like ones with more fluidity. Below 50% w/w PG, the mixtures of DSPC and PG resulted in no direct observation of LC structure through PM because they were very close to solid-states. From 55% w/w to 90% w/w of PG, the dense lamella crystalline structures were observed through PM, and their thickness and area decreased as the content of PG increased. Measured by DSC with heating process, the main phase transition from α -lamella phase to isotropic phase appeared from 52.89 °C to 47.41 °C to show linearly decreasing behaviors because PG affects the hydrophobic region of DSPC-based lamella phase. The repeating distance of the lamella phase and the interlayer distance between bilayers were calculated with XRDs and the average number of bilayers related to the thickness in LC structure was approximately estimated by combining with TEM results. The WAXS and DSC measurements showed that all of PG molecules contributed to swelling both the lipid layer in the edge region of lamella phase close to phosphate groups and the interlayer between bilayers below 90% w/w of PG. The phase and thermal behaviors were found to depend on the amount of PG used by means of dissolving DSPC as a phospholipid and rearranging its structure. Instead of water, the inducement of PG as a polar solvent in solid-lamella phase is discussed in terms of the swelling effect of PG for DSPC-based lamella membrane.

• Applied Chemistry for Engineering
• /
• v.21 no.6
• /
• pp.603-609
• /
• 2010

This paper aims to investigate the lyotropic behaviors of DSPC and CER3 when they are swollen by GLY as a solvent. The analyses were carried out on DSC, XRDs, PM, and Cryo-SEM. CER3 which has its high crystallinity and structural similarity with DSPC was well arranged up to 7.0 wt% in comparison to 20 wt% DSPC without any separation, but it was separated from the liquid crystalline (LC) phase to form another crystalline phase with the expression of its characteristic peak in XRDs and eutectic thermal behavior in DSC. Introducing CER3, two types of patterns were shown in XRD spectra; one is SPP expressed in a normal LC and another is LPP expressed in human skin SC. Therefore, it was confirmed that the incorporation of CER3 makes LC structure more similar to human skin. In Cryo-SEM study, it was shown that CER3 makes LC structure thicker and denser.