양전자 소멸시간 분광분석(Positron Annihilation Lifetime Spectroscopy)을 이용한 고분자 재료의 분자수준적 구조해석

곽승엽(Seung Yeop Kwak),김성호(Sung Ho Kim) 한국고분자학회 2005 고분자 과학과 기술 Vol.16 No.2

역삼투막용 고분자 소재

곽승엽(Seung Yeop Kwak),김창근(Chang Keun Kim),김재진(Jae Jin Kim) 한국고분자학회 1994 고분자 과학과 기술 Vol.5 No.2

The Building Energy Statistics using National Building Energy Integrated Management System

Kwak Young-Hoon(곽영훈),Shin Sung-Eun(신성은),Oh Seung-Yeop(오승엽),Kwon Oh-In(권오인) 한국태양에너지학회 2016 한국태양에너지학회 학술대회논문집 Vol.2016 No.10

Fouling-resistant microfiltration membrane modified with magnetite nanoparticles by reversible conjunction

Woo, Seung Taek,Yun, Taeseon,Kwak, Seung-Yeop Elsevier 2018 Separation and purification technology Vol.202 No.-

<P><B>Abstract</B></P> <P>We developed a stimuli-responsive poly(tetrafluoroethylene) (PTFE) microfiltration (MF) membrane by reversible conjunction of magnetite nanoparticles. We modified the magnetic particles with maleimide functional groups and attached them to a furan-modified PTFE membrane via a Diels–Alder (DA) cycloaddition reaction to prepare an anti-fouling membrane that responds to magnetism and temperature. The combined results of Fourier-transform infrared spectroscopy, X-ray diffractometry, vibrating sample magnetometry, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy investigations clearly showed that the maleimide-modified magnetic nanoparticles were successfully synthesized and coupled with the furan-modified PTFE MF membrane by the DA reaction. The modified membrane produced a micro-vortex under a rotating magnetic field, and showed a high resistance to fouling with a water flux higher than 50% of initial flux even after 30 min in the fouling test, whereas the neat membrane had a water flux falling below 20% of initial flux in 30 min. Moreover, the magnetite nanoparticles were readily and repeatedly regenerated on the MF membrane surface using a thermally driven peel-and-stick process; 75% of the water flux was recovered, even after three fouling cycles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A dual-stimuli-responsive membrane is developed. </LI> <LI> The thermo-reversible magnetic nanoparticles were successfully synthesized. </LI> <LI> The magnetite nanoparticles produced a micro-vortex on the membrane surface. </LI> <LI> The magnetite nanoparticles were detached and reattached by controlling temperature. </LI> <LI> The dual-stimuli-responsive PTFE membrane showed high fouling resistance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Tubular Superstructures Composed of α-Fe₂O₃ Nanoparticles from Pyrolysis of Metal–Organic Frameworks in a Confined Space: Effect on Morphology, Particle Size, and Magnetic Properties

Lee, Junhyung,Kwak, Seung-Yeop The American Chemical Society 2017 CRYSTAL GROWTH AND DESIGN Vol.17 No.9

<P>While preparation of metal oxide from metal organic frameworks (MOFs) has been widely studied, crystal growth via thermal decomposition of MOFs in a confined space is rarely investigated. We demonstrate a confinement effect on the crystal growth via pyrolysis of MOFs at high temperature. Iron containing MOF (Fe-MIL-88A) was calcined inside a SiO2. The crystalline phase, particle size, morphology, and magnetic properties of the synthesized iron oxide were characterized; alpha-Fe2O3 tubular structures that consisted of nanoparticles (around 10 nm) were observed. Studies of the magnetic properties show enhanced magnetization with superparamagnetic behavior. These results indicate that space confinement during the thermal treatment in air at high temperature allows the synthesis of small nanoparticles and the preservation of initial morphology of MOF precursors, which cannot be obtained via heating of MOFs without shell under identical conditions.</P>

Physical state of cellulose in BmimCl: dependence of molar mass on viscoelasticity and sol-gel transition

Ahn, Yongjun,Kwak, Seung-Yeop,Song, Younghan,Kim, Hyungsup The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.3

<P>In this work, we investigated the correlation between the molar mass and the rheological properties of cellulose/1-butyl-3-methylimidazolium chloride (BmimCl) solutions, and provided the depolymerization kinetics of cellulose in BmimCl. Gel permeation chromatography was used to track the change in molar mass and kinetics as a function of the dissolution time. The molar mass of cellulose in BmimCl decreased significantly as the dissolution time increased, following a zeroth order rate law. The decrease of inter-chain friction induced by depolymerization resulted in a lower viscosity, shorter relaxation time, and lower activation energy. The activation energies for flow were distinctly different above and below the critical molar mass, which indicates that the relaxation mechanisms were not identical above and below the critical molar mass. The transition behavior of liquid crystalline phase also changed at the critical molar mass, which strongly demonstrated the effect of chain length on the formation of cholesteric phase. The exponents of Mark-Houwink-Sakurada and the radius of gyration showed that cellulose in BmimCl existed as a Gaussian chain in a theta solvent.</P>

Efficient and selective removal of heavy metals using microporous layered silicate AMH-3 as sorbent

Kim, Jihoon,Kwak, Seung-Yeop Elsevier 2017 Chemical Engineering Journal Vol.313 No.-

<P><B>Abstract</B></P> <P>AMH-3 is a zeolite-like material with a three-dimensional uniform porous structure, layered structure, and abundant exchangeable cations. Herein, the use of AMH-3 to remove heavy metals present in aqueous solutions is investigated for the first time. Pristine AMH-3 and metal-sorbed AMH-3 were characterized with inductively coupled plasma atomic emission spectroscopy (ICP-AES), field emission scanning electron microscopy (FE-SEM), <SUP>29</SUP>Si cross polarization magic angle spinning nuclear magnetic resonance spectroscopy (CP MAS NMR) and X-ray diffraction (XRD). The removal of heavy metals by AMH-3 was found to be governed by ion exchange rather than surface adsorption, and no significant change occurred in the structure of the AMH-3 during the ion exchange. The removal of various heavy metal ions (Pb<SUP>2+</SUP>, Cu<SUP>2+</SUP>, Cd<SUP>2+</SUP>, and Zn<SUP>2+</SUP>) onto AMH-3 from aqueous solutions was conducted using a batch method. The effects of influential parameters, such as the initial metal ion concentration and contact time, on the sorption process were studied. The metal ion sorption capacity and removal efficiency were mainly dependent on the difference between the effective pore size of the AMH-3 and the hydrated radius of the metal ion. The sorption isotherm data were well fitted by Langmuir (for Pb<SUP>2+</SUP>, Cu<SUP>2+</SUP>, and Zn<SUP>2+</SUP>) and Freundlich (for Cd<SUP>2+</SUP>) models. The sorption kinetics data were well fitted by a pseudo-secondorder kinetic model. Competitive sorption experiments revealed an order of metal ion affinity of Pb<SUP>2+</SUP> >Cu<SUP>2+</SUP> >Zn<SUP>2+</SUP> >Cd<SUP>2+</SUP>. These findings indicate that AMH-3 is suitable for the efficient and selective removal of heavy metals from aqueous solutions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> AMH-3 has unique framework and abundant exchangeable cations. </LI> <LI> The removal of metal ions was governed by ion exchange rather than surface adsorption. </LI> <LI> AMH-3 exhibited a high sorption capacities for metal ions. </LI> <LI> Metal ions were selectively removed by AMH-3 pore size. </LI> </UL> </P>

Solvent-assisted heat treatment for enhanced chemical stability and mechanical strength of <i>meta</i>-aramid nanofibers

Chung, Junho,Kwak, Seung-Yeop Elsevier 2018 European polymer journal Vol.107 No.-

<P><B>Abstract</B></P> <P> <I>Meta</I>-aramid exhibits excellent chemical stability and mechanical strength owing to its rigid crystal structure. However, the crystal structure is destroyed when <I>meta</I>-aramid nanofibers (mANFs) are fabricated by electrospinning, which results in nanofibers with poor performance characteristics. Here, we present a facile solvent-assisted heat treatment for the efficient crystallization of mANFs. The optimal volume ratio of the co-solvent solution was determined to be 6:5:100 (DMAc:ethylene glycol:water), and the optimal crystallization temperature 120 °C. The crystallinity of the mANFs obtained under these optimized conditions (mANF-6-120) is higher than the crystallinity of mANFs heat-treated at 300 °C (mANF-HT). As a result, mANF-6-120 exhibits superior chemical stability and mechanical strength compared to mANF-HT. After immersion in DMAc for 48 h, the weight of mANF-6-120 is reduced to 28% of its original weight, whereas the relative remaining weight of mANF-HT is less than 8%. The value of Young’s modulus of mANF-6-120 is 1.7 times higher than that of mANF-HT. The crystallization process developed in this study requires less energy and is less expensive than the conventional high-temperature heat treatment process. The <I>meta</I>-aramid nanofiber mat obtained using the proposed process shows great promise for application to water purification and the treatment of polluted air.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We fabricated <I>meta</I>-aramid nanofibers via electrospinning. </LI> <LI> The as-synthesized <I>meta</I>-aramid nanofibers were treated by solvent-assisted thermal treatment. </LI> <LI> The <I>meta</I>-aramid nanofibers were effectively crystallized by the solvent-assisted thermal treatment at 120 °C. </LI> <LI> The highly crystallized nanofibers exhibited enhanced chemical stability and mechanical strength. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Stress Analysis of HTS Magnet for a 600 kJ SMES

Myung-Jin Park,Sang-Yeop Kwak,Woo-Seok Kim,Seung-Wook Lee,Seung-Yong Hahn,Ji-Kwang Lee,Jin-Ho Han,Kyeong-Dal Choi,Hyun-Kyo Jung,Ki-Chul Seong,Song-yop Hahn IEEE 2007 IEEE transactions on applied superconductivity Vol.17 No.2

<P>Auto tuning niching genetic algorithm was used to design optimal HTS magnets for the 600 kJ class SMES system under several design constraint conditions. Constraint conditions were operation loss of magnet (less than 2 W), inductance of magnet (less than 24 H), the number of double pancake coils (about 10 DPCs), the number of turns of DPC (less than 300 turns), outer diameter of DPC (close to 800 mm) and total length of HTS wire in a DPC (less than 500 m). As a result of optimum design, we obtained design parameters for the 600 kJ SMES magnet according to two operating currents, 360 A and 370 A. However, even though the HTS magnet was designed optimally in respect to the electromagnetics, consideration of mechanical integrity due to the stress by Lorentz force must not be neglected for the stable operation of the SMES system. Therefore, we developed a program, through the finite element method (FEM), for stress analysis due to Lorentz force in operation of the SMES system. In this paper, the stresses (radial and hoop stress) imposed on the designed HTS magnets were calculated by the program, and the results of stress analysis were discussed.</P>

Assembly of magnetite nanocrystals into spherical mesoporous aggregates with a 3-D wormhole-like pore structure

Yu, Byong Yong,Kwak, Seung-Yeop Royal Society of Chemistry 2010 Journal of materials chemistry Vol.20 No.38

<P>Spherical mesoporous magnetite (Fe<SUB>3</SUB>O<SUB>4</SUB>) aggregates with a wormhole-like pore structure were successfully synthesized for the first time using a single iron precursor (iron(<SMALL>III</SMALL>) ethoxide) and an amphiphilic poly(ethylene oxide)-<I>block</I>-poly(propylene oxide)-<I>block</I>-poly(ethylene oxide) triblock copolymer (PEO<SUB>100</SUB>–PPO<SUB>65</SUB>–PEO<SUB>100</SUB>) as a soft template. In this synthesis, the interaction between the iron precursor and the triblock copolymer self-assemblies in ethanol leads to the assembly of magnetite nanocrystals into spherical mesoporous aggregates. These aggregates were characterized using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, standard and high-resolution transmission electron microscopy, <SUP>57</SUP>Fe Mössbauer spectroscopy, and X-ray diffraction, confirming the formation of pure-phase Fe<SUB>3</SUB>O<SUB>4</SUB> particles with monodisperse morphology (about 130 nm in diameter), three-dimensional wormhole-like mesopores, and highly crystalline spinel structure. In addition, a formation mechanism for this material in the present system is proposed, based on the analysis of results. The mesoporous magnetite has a high specific surface area of 165.6 m<SUP>2</SUP> g<SUP>−1</SUP>, and relatively large pores with a mean size of 5.2 nm. The magnetic susceptibility data demonstrate that this material exhibits superparamagnetic behavior.</P> <P>Graphic Abstract</P><P>The individual spinel-structured magnetite nanocrystals (about 5 nm in diameter) self-assemble into spherical aggregates (∼ 130 nm in diameter) with a three-dimensional wormhole-like mesopore structure. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0jm01274b'> </P>