• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.369-372
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• 2010

As analyzing friability of HTPE and HTPB propellants, the following results could be derived. The friability of the tested propellants depended on its binder contents, mechanical property, and burning rate. It was decreased as burning rate was lowered and toughness was increased.

• Macromolecular Research
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• v.10 no.6
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• pp.365-368
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• 2002

Thermoplastic polyurethanes (TPUs) with different hard segment length has been prepared from a fixed molar ratio of poly(tetramethylene ether glycol), 4,4'-diphenylmethane diisocyanate, and 1,4-butanediol by different polymerization procedures. Results reveal that the on-set temperature of endotherms ( $T_{cc}$ ) due to the crystallization of hard segments by cooling the TPUs from melt and the peak temperature of endotherms due to the melting of hard segments ( $T_{mh}$ ) by heating the TPUs increased and levelled off with increasing the hard segment length of TPUs. It has also been observed that soft segment glass transition temperature ( $T_{gs}$ ) of TPU decreased slightly with increasing the hard segment length, which explains less mixing of soft segments and hard segments. In tensile measurement of TPUs, strain hardening is observed with increasing the hard segment length, which is attributed to the strain induced crystallization of soft segments.

• Macromolecular Research
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• v.11 no.1
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• pp.42-46
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• 2003

Cell attachment and proliferation on the polymer films of triblock copolymer(ester-ether)s comprising po1y (L-1actide) (PLLA) and poly (oxyethylene-co-oxypropylene)(PN) were investigated using 3T3 fibroblasts. It was found that on the tissue culture polystyrene(TCPS) and the PLLA control film the cells could spread well while on the copolymer films the cells showed a rounded morphology without spreading and proliferated weakly. Especially, little cells proliferated on the films of copolymer having a LN composition of 20 wt%. While the water absorption of the copolymer films increased with increasing PN content, the contact angle against water of copolymer films immersed in aqueous medium was almost identical, being slightly lower than that of the PLLA film. These properties were compatible with the results of cell attachment. The in vitro hydrolysis of the films of triblock and multiblock type copolymers was faster with increasing PN content. The increased hydrolyzability, the flexibility and the decreased cell attachment suggested that these copolymers may have high potential as biodegradable materials for medical use.

• Journal of Integrative Natural Science
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• v.9 no.1
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• pp.28-34
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• 2016

A number of chiral selectors have been developed and applied for enantiomer separation of a variety of chiral compounds. Among these chiral selectors are chiral crown ethers, a class of synthetic host polyether molecules that bind protonated chiral primary amines with high selectivity and affinity. In this paper, two important chiral crown ethers as chiral selectors of bis-(1,1'-binaphthyl)-22-crown-6 and (18-crown-6)-2,3,11,12-tetracarboxylic acid (18-C-6-TA) are focused. They have been widely used to resolve the enantiomers of chiral compounds containing a primary amino moiety using chiral stationary phases (CSPs) or chiral selectors by high-performance liquid chromatography (HPLC), capillary electrophoresis (CE) and so on in chirotechnology. Also, it was described that the commercially available covalent type HPLC CSPs derived from (+)- and (-)-18-C-6-TA have been developed and successfully applied for the resolution of various primary amino compounds including amino acids.

• Korean Journal of Materials Research
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• v.31 no.8
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• pp.427-432
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• 2021

This study uses silicone monomer, DMA, crosslinking agent EGDMA, and initiator AIBN as a basic combination to prepare hydrogel lenses using fluorine-based perfluoro polyether and iron oxide and zinc oxide nanoparticles as additives. After manufacturing the lens using iron oxide nanoparticles and zinc oxide nanoparticles, the optical, physical properties, and polymerization stability are evaluated to investigate the possibility of application as a functional hydrogel lens material. As a result of this experiment, it is found that the addition of the wetting material containing fluorine changes the surface energy of the produced hydrogel lens, thereby improving the wettability. Also, the addition of iron oxide and zinc oxide nanoparticles satisfies the basic hydrogel ophthalmic lens properties and slightly increases the UV blocking performance; it also increases the tensile strength by improving the durability of the hydrogel lens. The polymerization stability of the nanoparticles evaluated through the eluate test is found to be excellent. Therefore, it is judged that these materials can be used in various conditions as high functional hydrogel lens material.

• Journal of dental hygiene science
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• v.10 no.3
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• pp.177-183
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• 2010

This study was begun to search effect of contact angles of elastic rubber impression materials on the surface of working cast. Of elastic rubber impression materials with a Type III consistency, such as polysulfide, polyether and addition silicone, we selected one and then measured the contact angle after dripping a distilled water 3.3ml. Then, after pouring a dental anhydrite in three types of impression materials, we prepared a working cast and then examined its surface. Contact angle was measured using a full automatic contact angle measuring system (DM-700, KYOWA, Japan), and the surface of working cast was observed using a field emission scanning electron microscope (JSM-6700F, JEOL Ltd., JAPAN). The following results were obtained: 1) $Mean{\pm}SD$ (SD: standard deviation) of the initial contact angles were $91.3{\pm}20.5^{\circ}$ in the addition silicone materials, $90.0{\pm}2.2^{\circ}$ in the polyethers and $101.5{\pm}2.3^{\circ}$ in the polysulfides. These results indicate that mean values were similar but standard deviations of the three materials showed a great discrepancy. 2) As the time elapsed, addition silicone materials were found to have a contact angle decreased abruptly as compared with the remaining two types. That is, the initial contact angle was $91.3^{\circ}$ and it was abruptly decreased to $29.4^{\circ}$ after 25 seconds. 3) In the polyethers, the initial contact angle was $101.5^{\circ}$ and it was decreased to $90.7^{\circ}$ after 25 seconds. In the polysulfides, however, the initial contact angle was $90.0^{\circ}$ and it was $84.2^{\circ}$ after 25 seconds. This showed almost no changes in the initial contact angles. Moreover, its magnitude was greater than that seen in additional silicones. 4) There were significant differences in the contact angles between the three types of elastic rubber impression materials as the time elapsed (p<0.001). On an observation on the surface of working cast, addition silicone materials were found to have the most dense surface. This was followed by polysulfides and polyethers in a descending order.

• Korean Journal of Poultry Science
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• v.12 no.2
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• pp.127-134
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• 1985

Battery trial with 240 broiler chicks of Hubbard strain was conducted for a period of 2 weeks in order to compare the anticoccidical efficacy of polyether ionophorous antibiotics ; Maduramicin ammonium, Monensin and Salinomyc in sodium. The criteria used in these anticoccidial efficacy studies were anticoccidial index, growth rate, feed efficiency, mortality, lesion score and the number of oocysts produced after artificial inoculation with 70,000 sporulated oocysts of Eimeria tenella(90%) and E.necatrix (10%) to each bird. The result obtained are summarized as follow: 1. All groups medicated anticoccidial feed additives improved body weight gain and feed efficiency. However, it was found that the group medicated with Maduramicin showed better body weight gain (352.5 and 648.8 g) and feed efficiency(1.603 and 1.680) during the first and the second week experiments, 2. The mortality rate(4.2%) and lesion scores (1.72) of Maduramicin medicated group, from artificial coccidiosis were comparatively lower than those of other two medicated groups, 3. It was also found that oocyst output (0.25 ${\times}$ 10$^4$) in Maduramicin medicated group were lower than those of other two groups. 4. Anticoccidial indexes during the first week were 177.9 in Maduramicin medica-group, 158.7 in Salinomycin medicated group, 141.6 in Monensin medicated group and 78.0 in infected, nonmedicated group as compared with 200.0 in noninfected, nonmedicated group (NNC) 5. Anticoccidial indexes during the second week were 201.1 in Maduramicin group 184.0 in infected, nonmedicated group as compared with 200.0 in noninfected, nonmedicated group (NNC).

• Journal of the Korean Applied Science and Technology
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• v.34 no.1
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• pp.66-82
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• 2017

Organosilicone-based surfactants consist of hydrophobic organosilicone groups coupled to hydrophilic polar groups. Organosilicone surfactants have been widely used in many industrial fields starting from polyurethane foam to construction materials, cosmetics, paints & inks, agrochemicals, etc., because of their low surface tension, lubricity, spreading, water repellency and thermal and chemical stability, resulted from the unique properties of organosilicone. Especially, trisiloxane surfactants, having low molecular weight organosilicone as hydrophobe, exhibit low surface tension and excellent wettability and spreadability, leading to their applications as super wetter/super spreader, but have the disadvantage of vulnerability to hydrolysis. A variety of trisiloxane surfactant structures are required to provide the functional improvement and the defect resolution for reflecting the necessities in the various applications. This review covers the synthetic schemes of reactive trisiloxanes as hydrophobic siloxane backbones, the main reaction schemes, such as hydrosilylation reaction, for coupling reactive trisiloxanes to hydrophilic groups, and the synthetic schemes of the main trisiloxane surfactants including polyether-, carbohydrate-, gemini-, bolaform-, double trisiloxane-type surfactants.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.3
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• pp.253-260
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• 2016

This paper proposes a planar Log-Periodic Dipole Array(LPDA) antenna with light-weight supporting structure for installing on an aircraft. The proposed antenna is designed by applying a planar skeleton supporting structure that has light-weight for an aircraft and is capable of withstanding structural vibration. The material of the planar skeleton supporting structure is a Polyether ether ketone(Peek) which has excellent characteristics on strength and temperature. The proposed antenna is fabricated by attaching the radiating elements of the LPDA on both sides of the supporting structure. The changed input impedance due to the dielectric material of the supporting structure was compensated for by controlling the distance and length of several radiating elements. The 10-dB return loss bandwidths of the designed planar LPDA antenna with light-weight supporting structure are obtained as 0.4~3.1 GHz(7.3:1) in the simulation and 0.41~3.5 GHz(8.2:1) in the measurement. The average gains in 0.5~3 GHz band are 6.77 dBi in the simulation and 6.55 dBi in the measurement. Therefore, we confirm that the designed antenna is appropriate to be installed on an aircraft due to its light-weight structure and wideband directional radiation characteristics.

• Journal of the Korean Applied Science and Technology
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• v.34 no.3
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• pp.461-477
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• 2017

Organosilicone-based surfactants, consisting of hydrophobic organosilicone groups coupled to hydrophilic polar groups, have been widely used in many industrial fields starting from polyurethane foam to construction materials, cosmetics, paints & inks, agrochemicals, etc., because of their low surface tension, lubricity, spreading, water repellency and thermal and chemical stability, resulted from the unique properties of organosilicone. Especially, organosiloxane surfactants, having low molecular weight siloxane as hydrophobe, exhibit low surface tension and excellent wettability and spreadability, leading to their applications as super wetter/super spreader, but have the disadvantage of vulnerability to hydrolysis. A variety of low molecular weight siloxane surfactant structures are required to provide the functional improvement and the defect resolution for reflecting the necessities in the various applications. This review includes the synthetic schemes of reactive tetrasiloxanes and disiloxanes as hydrophobic siloxane backbones, the main reaction schemes, such as hydrosilylation reaction, for coupling reactive tetrasiloxanes or disiloxanes to hydrophilic groups, and the main synthetic schemes of the tetra- and di-siloxane surfactants having polyether-, carbohydrate-, gemini-, bola-type surfactant structures.