Euigyung Jeong

Agency for Defense Development, Sŏul, Seoul, South Korea

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Publications (29)73.02 Total impact

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    ABSTRACT: Multi-walled carbon nanotube (MWCNT)/epoxy composites were prepared using MWCNT fluorinated to different extents. The mechanical properties, fracture surface morphologies and electromagnetic interference shielding efficiency (EMI-SE) of these composites were evaluated for epoxy matrices containing MWCNT with degrees of fluorination. The tensile strengths of the MWCNT/epoxy composites improved by 31% with treated MWCNT compared to that of the epoxy composites with untreated MWCNT. The EMI-SE values of the fluorinated MWCNT/epoxy composites improved up to 26% with increasing fluorination extent. The mechanical and electrical properties enhancement of the composites were attributed to the fluorinated MWCNT, which improved both the dispersion of the MWCNT in epoxy matrix and interfacial interactions between the MWCNT and the epoxy matrix.
    No preview · Article · Feb 2016 · Applied Surface Science
  • Ji-Hyun Kim · Sangmin Lee · Euigyung Jeong · Young-Seak Lee
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    ABSTRACT: Graphite foams (GFs) were prepared by adding different amounts of mesophase pitch (MP) into polyvinyl alcohol-acrylic acid (PVA-AAc) solution followed by the heat treatment. It was confirmed that the pore diameters of GFs were controlled by the slurry concentration, which was the mesophase content added in polymer solution, and their thermal conductivity and compressive strength were also controlled by porosities of GFs formed at different conditions. The resulting GFs in this study had the highest thermal conductivity of 53.414 ± 0.002 W/mK and compressive strength of 1.348 ± 0.864 MPa at 0.69 in porosity. The thermal conductivity of MP based GFs increased approximately 23 times higher than that of using isotropic pitch based GFs due to the developed graphitic structure. © 2014 The Korean Society of Industrial and Engineering Chemistry. All rights reserved.
    No preview · Article · Dec 2015 · Journal of the Korean Industrial and Engineering Chemistry
  • Ji-Hyun Kim · Do Young Kim · Euigyung Jeong · Young-Seak Lee
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    ABSTRACT: To fabricate carbon foams with high compressive strength and thermal conductivity, carbon foams were prepared by curing and heat treatment of a polymer solution containing CMC, isotropic pitch and fluorinated CNTs. The CNTs were fluorinated at different fluorine gas pressures (F2:N2 =3:7, 5:5, and 7:3). The highly heat-treated carbon foams containing fluorinated CNTs prepared with F2:N2 =5:5 had the highest thermal conductivity of 3.18±0.01W/mK, and compressive strength of 2.42±0.22MPa, which were approximately 15% and 133% higher, respectively, than those of the highly heat-treated carbon foams containing un-fluorinated CNTs due to increased crystallinity of CNTs and their adhesion with pitches in highly heat-treated carbon foams through fluorination of CNTs.
    No preview · Article · Nov 2015 · Applied Surface Science
  • Ji-Hyun Kim · Euigyung Jeong · Young-Seak Lee
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    ABSTRACT: Graphite foams can be prepared by various methods, such as a blowing, the use of polymer based templates, and the compression of graphite and/or graphite sheets. Adding fillers to graphite foams can lead to improved thermal conductivity and compressive strength. The mechanical properties of graphite foam with carbon material added are negatively affected by the low dispersibility, alignment and interfacial adhesion of the fillers in the foam. This study reviews studies that have investigated various fabrication methods, the addition of carbon materials, and surface treatments of graphite foams to improve their thermal and mechanical properties. © 2015 The Korean Society of Industrial and Engineering Chemistry.
    No preview · Article · Sep 2015 · Journal of Industrial and Engineering Chemistry
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    ABSTRACT: We evaluated the use of polyethersulfone (PES) as reinforcement material to increase the mechanical and thermal properties of triglycidyl-p-aminophenol (TGAP) epoxy resin. The enhancement of the mechanical properties of the PES/epoxy composites was indicated by 44%, 35%, and 11% increases in tensile strength, impact strength, and fracture toughness, respectively. TGA revealed that the thermal stability of the PES/epoxy composites also improved by 17%, which was calculated using the integral procedural decomposition temperature (IPDT). These results are attributed to the good distribution and formation of the semi-interpenetrating polymer networks (semi-IPNs) that composed the epoxy network and the linear PES. © 2015 The Korean Society of Industrial and Engineering Chemistry.
    No preview · Article · Sep 2015 · Journal of Industrial and Engineering Chemistry
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    ABSTRACT: Poly(ether sulfone) (PES) embedded diglycidylether of bisphenol-A (DGEBA) epoxy composites were fabricated for improving its mechanical properties and thermal stability. The mechanical properties such as tensile, flexural and impact strength of the composites changed significantly with the introduction of PES. The value of the fracture toughness of this composite also was increased remarkably about 24%. Thermal stability of PES/epoxy composites also improved 12%, which was calculated with integral procedural decomposition temperature (IPDT). From the differential scanning calorimeter (DSC) result, the curing temperature and curing heat decreased according to the increase of PES contents. These were attributed to the good distribution and the formation of the semi-interpenetrating polymer networks (semi-IPNs) composed of the epoxy network and linear PES.
    No preview · Article · May 2015 · Polymer Korea
  • Min-Jung Jung · Euigyung Jeong · Young-Seak Lee
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    ABSTRACT: The surfaces of multi-walled carbon nanotubes (MWCNTs) were thermally fluorinated at various temperatures to enhance the electrochemical properties of the MWCNTs for use as electric double-layer capacitor (EDLC) electrodes. The fluorine functional groups were added to the surfaces of the MWCNTs via thermal fluorination. The thermal fluorination exposed the Fe catalyst on MWCNTs, and the specific surface area increased due to etching during the fluorination. The specific capacitances of the thermally fluorinated at 100 °C, MWCNT based electrode increased from 57 to 94 F/g at current densities of 0.2 A/g, respectively. This enhancement in capacitance can be attributed to increased polarization of the thermally fluorinated MWCNT surface, which increased the affinity between the electrode surface and the electrolyte ions.
    No preview · Article · Apr 2015 · Applied Surface Science
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    ABSTRACT: Mutli-walled carbon nanotubes (MWCNTs) were surface-modified by a hydrofluoric acid solution to remove impurities and improve interfacial bonding and dispersion of nanotubes in an epoxy matrix. The crystallinity on the surface of treated MWCNTs was investigated by X-ray photoelectron spectroscopy and Raman spectroscopy. The mechanical properties were characterized by tensile test, and the enhancement of mechanical properties of the modified MWCNTs/epoxy composites was indicated by a 33% increase in tensile strength. The electromagnetic interference shielding effectiveness (EMI-SE) of modified MWCNTs/epoxy composites was improved with an increase in concentration of hydrofluoric solution, and EMI-SE showed the maximum increase with 25% HF. However, mechanical and EMI-SE properties didn't show further increase with over 50% HF concentration because the properties of MWCNTs were influenced by degradation of crystallinity and intrinsic properties of MWCNTs. The mechanical and electrical property enhancements of the polymer composites are attributed to the modification of MWCNTs which improve crystallinity of MWCNTs and dispersion in the epoxy resin.
    No preview · Article · Jan 2015 · Polymer Korea
  • Mi-Seon t Park · Seho Cho · Euigyung Jeong · Young-Seak Lee
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    ABSTRACT: The pitch-based high crystallinity cokes are investigated by evaluating its potential as electrode materials for electric double layer capacitors (EDLCs). After activation process, the high crystallinity cokes-based activated carbon (hc-AC) demonstrates great potential for use as an electrode material for EDLCs. The specific capacitance of hc-AC with the carbon to KOH ratio of 1:3 is 276 F g−1, even with a low specific surface area of 983 m2 g−1. These results are comparable to that of the most commonly used material for EDLCs, MSP 20 (256 F g−1), which has a high specific surface area of 1807 m2 g−1.
    No preview · Article · Jul 2014 · Journal of Industrial and Engineering Chemistry
  • Min-Jung Jung · Euigyung Jeong · Yesol Kim · Young-Seak Lee
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    ABSTRACT: To investigate the relationship between textural properties and electrochemical properties, activated carbon nanofibers were manufactured using an electrospinning process followed by chemical activation using KOH or NaOH. The specific surface area of the KOH-activated carbon nanofibers was higher than that of NaOH-activated carbon nanofibers; however, the total pore volume and mesopore volume of the NaOH-activated carbon nanofibers were greater than those of the KOH-activated carbon nanofibers when the same number of moles of KOH and NaOH were used. The specific capacitances increased as the specific surface area and pore volume of the activated carbon nanofibers were increased. However, the specific capacitance obtained at a high scan rate (50 mV/s) and the retained capacitance of the activated carbon nanofibers increased with increasing total pore and mesopore volume, especially for mesopores with diameters of 2–4 nm.
    No preview · Article · Jul 2013 · Journal of Industrial and Engineering Chemistry
  • Euigyung Jeong · Min-Jung Jung · Young-Seak Lee
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    ABSTRACT: In this study, we investigated the role of fluorination in improving the electrochemical properties of activated carbon nanofiber (ACNF) electrodes. The ACNFs were prepared with various textural properties and then fluorinated. The electrochemical properties of the resulting ACNFs were subsequently evaluated to investigate the effect of the fluorination of the prepared ACNFs with various textural properties on the electrochemical properties. The specific capacitances of the ACNF electrodes increased by 15.8–47.3% after fluorination, although the specific surface area and the total pore volume decreased significantly; these results suggest that the introduction of CF functional groups onto the ACNF surface was more important than the induction of changes in the textural properties of the ACNF samples with respect to improving the electrochemical properties of the ACNF electrodes. The retained capacitances of the ACNF electrodes also increased 2–12% after fluorination, although the etching effect of the fluorination significantly collapsed the mesopores; these results suggest that the CF functional groups were electrochemically active even at a high scan rate.
    No preview · Article · Jun 2013 · Journal of Fluorine Chemistry
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    ABSTRACT: This study investigated the potential of direct fluorination as a multifunctional surface modification method for an aramid fabric. The aramid fabric was fluorinated at temperatures of 30, 90, and 150 °C. As the fluorination temperature increased, the fluorinated aramid fabric became more hydrophobic and oleophobic, with a water contact angle of 129.3° and a diiodomethane contact angle of 108.6° when the fluorination temperature was 150 °C. Thus, the fluorinated fabric could be defined as an omniphobic surface. Both the phenol resin wettability and the impregnation of the fluorinated aramid fabric improved as the fluorination temperature increased, suggesting better interfacial adhesion between the fabric and the polymer matrix. Direct fluorination of an aramid fabric can be an efficient multifunctional surface modification method to achieve omniphobicity in the aramid fabric for the protection, self-cleaning, and improved interfacial adhesion between the fabric and resin for fiber-reinforced polymer composites.
    No preview · Article · Sep 2012 · Journal of Fluorine Chemistry
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    ABSTRACT: The surface of phenol-based activated carbon (AC) was seriatim amino-fluorinated with solution of ammonium hydroxide and hydrofluoric acid in varying ratio to fabricate electrode materials for use in an electric double-layer capacitor (EDLC). The specific capacitance of the amino-fluorinated AC-based EDLC was measured in a 1 M H(2)SO(4) electrolyte, in which it was observed that the specific capacitances increased from 215 to 389 Fg(-1) and 119 and 250 Fg(-1) with the current densities of 0.1 and 1.0 Ag(-1), respectively, in comparison with those of an untreated AC-based EDLC when the amino-fluorination was optimized via seriatim mixed solution of 7.43 mol L(-1) ammonium hydroxide and 2.06 mol L(-1) hydrofluoric acid. This enhancement of capacitance was attributed to the synergistic effects of an increased electrochemical activity due to the formation of surface N- and F-functional groups and increased, specific surface area, and mesopore volumes, all of which resulted from the amino-fluorination of the electrode material.
    No preview · Article · May 2012 · Journal of Colloid and Interface Science
  • Min-Jung Jung · Euigyung Jeong · Sang Ick Lee · Young-Seak Lee
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    ABSTRACT: To improve the electrochemical performance of an activated carbon (AC)-based electric double-layer capacitor (EDLC), the AC surface, which is used as an electrode, was modified using physicochemical base tuning that uses different concentrations of ammonium hydroxide. The effect of the treatment on the surface and electrochemical properties of the AC electrodes was investigated. The specific capacitance of a 13 vol%-solution-treated sample was increased to 385 F/g at a scan rate of 5 mV/s, which was 17% higher than the value of 328 F/g obtained for the untreated samples. This increase can be attributed to an increase in the mesopore volume ratio due to the etching effect of the reaction between the carbon surfaces and ammonium hydroxide. Moreover, nitrogen functional groups, which were introduced by the treatment, also improved the electrochemical properties of the resulting AC-based electrode. Therefore, a simultaneous etching and nitrogen-introducing method with ammonium hydroxide can easily introduce nitrogen functional groups on the surface of an AC electrode. This method is very effective for preparing AC for use in an EDLC with improved electrochemical properties.
    No preview · Article · Mar 2012 · Journal of Industrial and Engineering Chemistry
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    ABSTRACT: To improve the electrical performance of activated carbon (AC)-based electric double-layer capacitors (EDLCs), the surface of AC was modified with gas phase ammonia treatment at 1073 K with different treatment times to carry out simultaneous etching and N-doping. The effects of the treatment on AC surfaces and their electrochemical properties were investigated. The specific capacitances of samples treated for 22 min were increased to 426 F/g at scan rates of 10 mV/s, which corresponded to a 76.8% increase as compared with 241 F/g of samples measured as received from the manufacturer. The increase is attributed to an increase in the specific surface area and the total pore, micro- and mesopore volumes due to the etching effect of the high-temperature ammonia gas reaction. Moreover, N-functional groups, which were introduced by the treatment, also aided to improve the electrochemical properties of the resulting AC-based electrode. Therefore, the simultaneous etching and N-doping method with ammonia gas at high temperature can easily introduce nitrogen functional groups on the AC surface. In addition, the reaction of nitrogen gas with AC can affect its specific surface area and surface pore structure, which is very effective in preparing AC for EDLCs with improved electrochemical properties.
    No preview · Article · Jan 2012 · Journal of Industrial and Engineering Chemistry
  • Jinhoon Kim · Euigyung Jeong · Young-Seak Lee
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    ABSTRACT: This study reports the application of illite as a clay filler and direct fluorination as an organophilic modification for clays. Illite was also modified using conventional methods, with reagents such as 3-aminopropyltrimethoxysilane and hexadecyl-trimethoxysilane for comparison of the resultant illite/polypropylene (PP) composites with the fluorinated illite/PP composites. The thermal properties, flame retardancy, and mechanical properties of the resultant composites were also investigated. Fluorination of illite resulted in exfoliation and more thermally stable organophilic modification compared with the conventional silane treatment. When comparing two different silane-treated illite/PP composites with fluorinated illite/PP composites, fluorinated illite had better thermal stability and exfoliation after modification and more improved dispersion in PP matrix. This resulted in improved thermal stability, flame retardancy, and mechanical properties compared with the silane-treated illite/PP composites. The fluorinated illite/PP composite exhibited a 28% increase in thermal stability and a 50% increase in flame retardancy compared with neat PP. Fluorination of illite yielded at least 50% further improvement in the thermal stability and flame retardancy of the resulting illite/PP composites compared with the conventional silane treatments.
    No preview · Article · Jan 2012 · Journal of Materials Science
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    ABSTRACT: The surface of phenol-based activated carbon (AC) was fluorinated at room temperature with different F2:N2 gas mixtures for use as an electrode material in an electric double-layer capacitor (EDLC). The effect of surface fluorination on EDLC electrochemical performance was investigated. The specific capacitance of the fluorinated AC-based EDLC was measured in a 1 M H2SO4 electrolyte, in which it was observed that the specific capacitances increased from 375 and 145 F g−1 to 491 and 212 F g−1 with the scan rates of 2 and 50 mV s−1, respectively, in comparison to those of an unfluorinated AC-based EDLC when the fluorination process was optimized via 0.2 bar partial F2 gas pressure. This enhancement in capacitance can be attributed to the synergistic effect of increased polarization on the AC surface, specific surface area, and micro and mesopore volumes, all of which were induced by the fluorination process. The observed increase in polarization was derived from a highly electronegative fluorine functional group that emerged due to the fluorination process. The increased surface area and pore volume of the AC was derived from the physical function of the fluorine functional group.
    No preview · Article · Dec 2011 · Journal of Fluorine Chemistry
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    ABSTRACT: The surface of a phenol-based activated carbons (ACs) used as an electrode in an electric double-layer capacitor (EDLC) was oxyfluorinated at room temperature with different F2:O2 gas mixtures, and the effects of these surface modifications on EDLC electrical performance were investigated. The specific capacitance of the oxyfluorinated AC-based EDLC was measured in a 1 M H2SO4 electrolyte, in which it was observed that the specific capacitances increased from 375 and 145 F g−1 to 391 and 189 F g−1 with the scan rates of 5 and 50 mV s−1, respectively, over compared to those of an untreated AC-based EDLC when the oxyfluorination ratio was at the optimal F2:O2 = 5:5. This was attributed to the synergistic effect of surface chemical compositions and textural properties of the resulting oxyfluorinated AC, which had the highest micropore volume, an optimal mesopore volume, and electrochemically active surface functional groups, such as C–F and quinone CO.
    No preview · Article · Sep 2011 · Colloids and Surfaces A Physicochemical and Engineering Aspects
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    ABSTRACT: A high-performance NO gas sensor was prepared by inducing thermal fluorination of carbon nanotube semiconductors. Thermal fluorination of multi-walled carbon nanotubes (MWCNTs) was carried out at various temperatures (100 ∼ 1000 °C) to investigate the effects of the reaction temperature. The mechanism of high-performance NO gas sensor electrode was shown to depend on the fluorination temperature in a way that can be divided into three regions, separated at 400 and 1000 °C. In the first temperature region, the induction of fluorine functional groups onto MWCNTs showed the opposite trend in electrical resistance change comparing with traditional p-type MWCNTs. In the second temperature region, the induced fluorine functional groups were attenuated by generated fluorinated carbon gases resulting in the decomposition of MWCNTs and the recovery of traditional p-type gas sensor behavior. In the highest temperature region above 1000 °C, reoriented carbon structure was observed, showing bent nanotubes produced from destruction by fluorination and subsequent reorientation due to the high temperature. The gas sensing responsiveness was significantly improved by the thermal fluorination, which causes electrophilic attraction, creates adsorption sites for target NO gases and improve hydrophobicity for gas sensing stability in humid condition. In conclusion, a high-performance gas sensor was obtained by thermal-fluorination of MWCNTs.
    No preview · Article · Jun 2011 · Carbon
  • Euigyung Jeong · Jinhoon Kim · Se Ho Cho · Yeon-Sook Bae · Young-Seak Lee
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    ABSTRACT: Oxy-fluorination of carbon preforms with various F2:O2 gas mixtures were examined to improve the mechanical and thermal properties of carbon fiber-reinforced carbon composites (C/C composites). The oxy-fluorination of the preforms introduced functional groups onto the preform surface, which improved their thermal properties. Oxy-fluorination also improved the interfacial adhesion of the C/C composites, resulting in increased flexural strength and anti-oxidation. Two synergistic effects of oxy-fluorination on the carbon preform are suggested. One optimizes interfacial adhesion by forming hard chemical bonds and soft electrophilic bonds between the surface functional groups of the oxy-fluorinated carbon preforms and the functional groups of the carbon precursors. The other improves anti-oxidation of the C/C composites by improving the thermal properties of the carbon preform itself and interfacial adhesion which resulted in reducing pores, voids, and interfacial cracks.
    No preview · Article · Apr 2011 · Journal of Fluorine Chemistry