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Temperature and magnetic field dependent optical properties of superconducting $MgB_2$ thin film
정종훈,이해자,김경완,김명훈,노태원,강원남,정창욱,이성익,Jung, J. H.,Lee, H. J.,Kim, K. W.,Kim, M. W.,Noh, T. W.,Wang, Y. J.,Kang, W. N.,Jung, C. U.,Lee, Sung-Ik 한국초전도학회 2001 Progress in superconductivity Vol.3 No.1
We investigated the temperature and magnetic field dependent optical properties of a$ MgB_2$ thin film in the far-infrared region. In the superconducting state, i.e. 5 K, we obtained the values of superconducting gap $2\Delta$ ~ 5.2 meV and $2\Delta$ $_{k}$ $B/T_{c}$ ~1.8. Although the value of$ 2\Delta$</TEX$B/T_{c}$ was nearly half of the BCS value, the $2\Delta$ seemed to follow the temperature dependence of the BCS formula. Under the magnetic field (H), the superconducting state became suppressed. Interestingly, we found that the normal state area fraction abruptly increased at low field but slowly increased at high field. It did not follow the H-dependences predicted for a s-wave superconductor (i.e. a linear dependence) nor for a s-wave one (i.e. $H^{1}$2/ dependence). We discussed the complex gap nature of $MgB_2$ in comparison with two gap and anisotropic s-wave scenarios.ios.
정종훈,정희정,유성구,최현국,서길수 한국공업화학회 2002 응용화학 Vol.6 No.1
Poly(acrylic acid)/Na-MMT superabsorbent nanocomposite was synthesized. Acrylic acid(AA) used as a monomer, N,N'-methylenebis-acrylamide was used as a crosslinker, and potassium persulfate was used as an initiator. Absorption amount of water at the superabsorbent nanocomposite was 311 to 801 times of' superabsorbent nanocomposite weight. Superabsorbent nanocomposite with a water absorbency higher than 801g H_2O/g was synthesized having 0.10 wt% crosslinker, 1.8 wt% initiator, 10 wt % Na-MMT, a neutralization degree of 65 % and a reaction temperature of 70℃.
Poly(N-isopropylacrylamide)/Silica 복합재료에 관한 연구
정종훈,서길수 한국공업화학회 2002 응용화학 Vol.6 No.2
Thermosensitive poly(N-isopropylacrylamide) (PNIPAM) composite exhibit a unique phase change at its lower critical solution temperature(LCST). The properties of PNIPAM nanocomposite make it a good candidate material for many applications, such as in articial muscles, drug delivery system, reversible surfaces, separation membranes, enzyme immobilization, catalysis substrates, actuators, and chemical valves. Thermal responsive composite were synthesized by two step. In the first step, N-isopropylacrylamide and methylene bisacrylamide as crosslinking agent was copolymerized at 65 ℃ and generated the silica in PNIPAM network by in-situ precipitation method as second step. Hydrogel containing silica exhibited a LCST similar to PNIPAM hydrogel. However, tensile strength showed that the mechanical property of thermoresponsive PNIPAM composites was improved compared to PNIPAM without silica filler.
Poly(ethylene oxide)/메조포어 실리카 복합재료에 관한 연구
김영식,유성구,정종훈,서길수,김동준 한국공업화학회 2002 응용화학 Vol.6 No.1
Mesopouous siliica material was synthesized under acidic conditions in the presence of cationic surfactant as templating species. It has been studied the penetration phenomena of polyethylene oxide(PEO) into mesoporous silica. From the result of X-ray diffraction(XRD) experiments, polymer/mesoporous silica sample has been showed that pore size hasn't been changed even polymer were penetrated into pores of mesoporous silica. It was known that the amount of PEO chains penetrated into mesoporoussilica pores has large effect on the reaction time. And the ares of the endotherm corresponding to the crystalline PEO was reduced by the study of differential scanning calorimetry(DSC)
Foaming 조건에 따른 PMMA microcellular foam의 구조 연구
김영식,배효광,유성구,정종훈,서길수 한국공업화학회 2002 응용화학 Vol.6 No.1
Supercritical carbon dioxide is known to swell and plasticize poly(methyl methacrylate), PMMA, dramatically. In this paper, a basic characterization of the solid-state foam processing is presented. Experiments were conducted in order to determine the effect of foaming temperature and foaming time on cell structures, cell density, and so on. As a result, Higher foaming temperature and foaming time generated larger cell size, and lower cell density.