Publications (24)99.33 Total impact
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Article: Preparation of single-walled carbon nanotube (SWNT) gel composites using poly(ionic liquids)
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ABSTRACT: This paper reports a new and practical route for synthesizing nanotube-polymeric ionic liquids gel by non-covalent functionalization of oxidized single-walled carbon nanotube (SWNT) surfaces with imidazolium-based poly(ionic liquids) (PILs), using in situ radical polymerization method. A black and homogeneous precipitate SWNTs was obtained as a gel form, which is well dispersed in aqueous solution without any aggregation. The formation of SWNT gels is explained by the electrostatic attractions or π-bonds between the SWNT surface and the PIL matrix. By anion-exchange reaction of PIL bound to SWNTs, hydrophilic anions in PIL were substituted with hydrophobic anions, resulting in an effective transfer of SWNT-PIL hydrogels to organogels. The result also showed that SWNTs can effectively improve the conductivity along with the thermal stability of nanocomposite gels. KeywordsCarbon nanotubes-Nanocomposite-Hydrogels-OrganogelsColloid and Polymer Science 04/2012; 288(9):1013-1018. · 2.33 Impact Factor -
Article: Large-scale graphene micropatterns via self-assembly-mediated process for flexible device application.
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ABSTRACT: We report on a method for the large-scale production of graphene micropatterns by a self-assembly mediated process. The evaporation-induced self-assembly technique was engineered to produce highly ordered graphene patterns on flexible substrates in a simplified and scalable manner. The crossed stripe graphene patterns have been produced over a large area with regions consisting of single- and two-layer graphene. Based on these graphene patterns, flexible graphene-based field effect transistors have been fabricated with an ion-gel gate dielectric, which operates at low voltages of < 2 V with a hole and electron mobility of 214 and 106 cm(2)/V·s, respectively. The self-assembly approach described here may pave the way for the nonlithographic production of graphene patterns, which is scalable to large areas and compatible with roll-to-roll system.Nano Letters 02/2012; 12(2):743-8. · 13.20 Impact Factor -
Article: Electromagnetic properties of Fe3O4-functionalized graphene and its composites with a conducting polymer
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ABSTRACT: Hybrid materials of Fe3O4-decorated reduced gra- phene oxide (Fe3O4-RGO) and poly(3,4-ethylenedioxythio- phene) (PEDOT) were prepared by poly(ionic liquid)-mediated hybridization. In this hybrid material, poly(ionic liquid) was found to perform multiple roles for: (1) stabilizing Fe3O4-RGO against aggregation in the reaction medium, (2) transferring Fe3O4-RGO nanomaterials from aqueous into organic phase, and (3) associating Fe3O4-RGO nanomaterials with PEDOT. The hybrid materials of Fe3O4-RGO with PEDOT showed the lowest surface resistivity of 80 X sq1 at an RGO-Fe3O4 loading of 1 wt %, and exhibited superparamagnetic behavior with an electromagnetic interference shielding effectiveness of 22 dB.Journal of Polymer Science Part A Polymer Chemistry 01/2012; 50(5):927-935. · 3.92 Impact Factor -
Article: Preparation and characterization of graphene composites with conducting polymers
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ABSTRACT: We report a new route for preparing electro-conductive composites based on reduced graphene oxide (RG-O) and poly(3,4-ethylenedioxythiophene) (PEDOT). The composites were prepared by in situ polymerization of EDOT in aqueous mixture containing RG-O platelets modified with poly(sodium 4-styrenesulfonate) (PSS). In the synthetic process, PSS molecules stabilize RG-O in the aqueous phase and function as a polymerization template to hybridize PEDOT chains along RG-O platelets. Compared with the RG-O platelets, the resulting composites show an enhanced electrical conductivity of 9.2 S cm −1 with good thermal stability.Polymer International 08/2011; 61:93-98. · 1.90 Impact Factor -
Article: Shape-controlled synthesis of silver crystals mediated by imidazolium-based ionic liquids.
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ABSTRACT: This work presents an approach toward the shape-controlled synthesis of Ag crystals with hierarchical structures by exploitation of ionic liquids (ILs) as a shape-regulating agent. The synthesis of Ag crystals involves the reduction of AgNO(3) by EG in the presence of ILs, specifically 1-butyl-3-methylimidazolium methylsulfate (bmim-MeSO(4)). In accordance with non-classical crystallization growth mechanism, the primary Ag nanoparticles were formed at the early stage of the reaction, and then self-organized into 1D or 3D Ag superstructures via an IL-mediated self-assembly process. Their final morphologies were strongly dependent on the reaction conditions such as the concentration of ILs in the reaction mixture and the reaction temperature, which suggests that ILs play an important role in controlling the shape of the Ag crystals.Physical Chemistry Chemical Physics 08/2011; 13(36):16138-41. · 3.57 Impact Factor -
Article: Self-organized graphene patterns.
Advanced Materials 04/2011; 23(24):2734-8. · 13.88 Impact Factor -
Article: High-performance supercapacitors based on poly(ionic liquid)-modified graphene electrodes.
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ABSTRACT: We report a high-performance supercapacitor incorporating a poly(ionic liquid)-modified reduced graphene oxide (PIL:RG-O) electrode and an ionic liquid (IL) electrolyte (specifically, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide or EMIM-NTf(2)). PIL:RG-O provides enhanced compatibility with the IL electrolyte, thereby increasing the effective electrode surface area accessible to electrolyte ions. The supercapacitor assembled with PIL:RG-O electrode and EMIM-NTf(2) electrolyte showed a stable electrochemical response up to 3.5 V operating voltage and was capable of yielding a maximum energy density of 6.5 W·h/kg with a power density of 2.4 kW/kg. These results demonstrate the potential of the PIL:RG-O material as an electrode in high-performance supercapacitors.ACS Nano 01/2011; 5(1):436-42. · 10.77 Impact Factor -
Article: Nanocomposites of single-walled carbon nanotubes and poly(3,4-ethylenedioxythiophene) for transparent and conductive film
Organics Electronic. 03/2010; -
Article: Synthesis of phase transferable graphene sheets using ionic liquid polymers.
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ABSTRACT: A practical route to the production of solution phase transferable graphene sheets using ionic liquid polymers (PIL) as a transferring medium is developed. Chemically converted graphene sheets decorated with PIL were found to be stable against the chemical reduction and well dispersed in the aqueous phase without any agglomeration. Upon the anion exchange of the PIL on graphene sheets, these PIL-modified graphene sheets in aqueous phase are readily transferred into the organic phase by changing their properties from hydrophilic to hydrophobic.ACS Nano 02/2010; 4(3):1612-8. · 10.77 Impact Factor -
Article: Poly(ionic liquid)-mediated hybridization of single-walled carbon nanotubes and conducting polymers.
Chemistry - An Asian Journal 02/2010; 5(2):256-60. · 4.50 Impact Factor -
Article: Poly(3,4-ethylenedioxythiophene) Derived from Poly(ionic liquid) for the Use as Hole-Injecting Material in Organic Light-Emitting Diodes.
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ABSTRACT: We report that poly(3,4-ethylenedioxythiophene) derived from poly(ionic liquid) (PEDOT:PIL) constitutes a unique polymeric hole-injecting material capable of improving device lifetime in organic light-emitting diodes (OLEDs). Imidazolium-based poly(ionic liquid)s were engineered to impart non-acidic and non-aqueous properties to PEDOT without compromising any other properties of PEDOT. A fluorescent OLED was fabricated using PEDOT:PIL as a hole-injection layer and subjected to a performance evaluation test. In comparison with a control device using a conventional PEDOT-based material, the device with PEDOT:PIL was found to achieve a significant improvement in terms of device lifetime. This improvement was attributed to a lower indium content in the PEDOT:PIL layer, which can be also interpreted as the effective protection characteristics of PEDOT:PIL for indium extraction from the electrodes.Macromolecular Rapid Communications 09/2009; 30(17):1477-82. · 4.60 Impact Factor -
Article: Ionic-liquid-assisted formation of silver nanowires.
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ABSTRACT: Down to the wire: A simple and effective method to synthesize silver nanowires through an ionic-liquid-assisted polyol process is developed (see scheme; scale bar=5 nm). The ionic liquids are tuned to provide the anisotropic growth of silver nanoparticles into nanowires.Angewandte Chemie International Edition 05/2009; 48(21):3806-9. · 13.45 Impact Factor -
Article: Organic solvent dispersion of poly(3,4‐ethylenedioxythiophene) with the use of polymeric ionic liquid
Journal of Polymer Science Part A Polymer Chemistry 09/2008; 46(20):6872 - 6879. · 3.92 Impact Factor -
Article: Water treeing, AC breakdown, and dielectric loss characteristics of EVA‐OH as a function of conversion rate
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ABSTRACT: Four kinds of ethylene–vinyl acetate–vinyl alcohol (EVA–OH) terpolymers containing different contents of hydroxyl groups were prepared using the transesterification reaction between a ethylene–vinyl acetate (EVA) copolymer and alcohol. Structural and thermal analyses of the EVA-OH produced were performed with Fourier transform infrared spectroscopy and differential scanning calorimetry. Electrical properties such as water treeing, AC breakdown, and dielectric loss characteristics were investigated. It was found that both water tree length and the probability of water tree generation decreased as a function of hydroxyl group content. AC breakdown characteristics such as average breakdown strength and characteristic breakdown strength (breakdown probability = 63.2%) of EVA improved as a function of the conversion rate of EVA-OH from acetate to hydroxyl groups. Dielectric loss increased with hydroxyl group content in the low-frequency range. In contrast, it was observed that dielectric loss decreased with hydroxyl group content in the high-frequency range. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 420–424, 2006Journal of Applied Polymer Science 04/2006; 101(1):420 - 424. · 1.29 Impact Factor -
Article: Compatibilizing Effect of SEBS for Electrical Properties of LDPE/PS Blends
Macromolecular Materials and Engineering 01/2006; 291(2):109 - 113. · 1.99 Impact Factor -
Article: Effects of alcoholic solvents on the conductivity of tosylate‐doped poly(3,4‐ethylenedioxythiophene) (PEDOT‐OTs)
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ABSTRACT: The effects of alcoholic solvents on the charge transport properties of tosylate-doped poly(3,4-ethylenedioxythiophene) (PEDOT-OTs) are investigated. The use of different alcoholic solvents in the oxidative chemical polymerization of 3,4-ethylenedioxythiophene (EDOT) with iron(III)-p-tosylate led to a change in the electrical conductivity of PEDOT-OTs. For example, PEDOT-OTs prepared from methanol shows a conductivity of 20.1 S cm−1 which is enhanced by a factor of 200 as compared to PEDOT-OTs prepared from hexanol. The variation of charge transport properties on the use of different alcoholic solvents is consistent with the data recorded by UV-visible and electrospin resonance (ESR) measurements. From XPS experiments, the PEDOT-OTs samples prepared from different alcoholic solvents were found to have almost the same doping level, suggesting that the number of charge carriers is not responsible for the change in conductivity. Supported by XRD results, it was found that the use of alcoholic solvents with shorter chain length induces more efficient packing of PEDOT chains. It is proposed that the alcoholic solvents associated with the counter ion of PEDOT via hydrogen bonding give rise to a change in the molecular ordering of PEDOT chains during the polymerization step, hence enhancing or depressing the inter-chain hopping rate of the resulting PEDOT-OTs. Copyright © 2005 Society of Chemical IndustryPolymer International 11/2005; 55(1):80 - 86. · 1.90 Impact Factor -
Article: Effects of poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] on the charge distributions of low‐density polyethylene/polystyrene blends
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ABSTRACT: The effect of the triblock copolymer poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) on the formation of the space charge of immiscible low-density polyethylene (LDPE)/polystyrene (PS) blends was investigated. Blends of 70/30 (wt %) LDPE/PS were prepared through melt blending in an internal mixer at a blend temperature of 220 °C. The amount of charge that accumulated in the 70% LDPE/30% PS blends decreased when the SEBS content increased up to 10 wt %. For compatibilized and uncompatibilized blends, no significant change in the degree of crystallinity of LDPE in the blends was observed, and so the effect of crystallization on the space charge distribution could be excluded. Morphological observations showed that the addition of SEBS resulted in a domain size reduction of the dispersed PS phase and better interfacial adhesion between the LDPE and PS phases. The location of SEBS at a domain interface enabled charges to migrate from one phase to the other via the domain interface and, therefore, resulted in a significant decrease in the amount of space charge for the LDPE/PS blends with SEBS. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2813–2820, 2004Journal of Polymer Science Part B Polymer Physics 06/2004; 42(15):2813 - 2820. · 1.53 Impact Factor -
Conference Proceeding: ESD protection materials using conductive polymers
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ABSTRACT: Clear conductive polymer films were prepared by coating the solution composed of conductive polymer and their properties were evaluated. Conductive polymer coated polymer films are transparent and have good ESD properties enough to be used as ESD protection materials for packaging electronic parts. 0.5 mm thick A-PET film with a surface resistance of 10<sup>5</sup> ohms per square shows a transparency at 550 nm of higher than 80%. Other properties such as cleanliness were also described. In addition, the application to other products such as cover films for carrier tapes, interleaf films for flexible printed circuit boards are introduced.2002 Electrical Overstress/Electrostatic Discharge Symposium, 2002. EOS/ESD '02.; 11/2002 -
Article: Charge distribution and conduction characteristics of 2-vinylpyridine-grafted polyethylenes
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ABSTRACT: This article describes electrical properties such as space charge distribution and electrical conduction characteristics of 2-vinylpyridine (VP) grafted low density polyethylenes (PE). The VP incorporated onto PE chains changes electrical properties of PE. For example, the homocharge found in virgin PE decreases with the increase of graft ratio. As a result of the nitrogen acting as an electron donor, no space charge develops at high graft ratios. It has been found that VP reduces the current density in PE. Grafted PE with VP content of 0.754 wt % has also been found to obey a space charge limited conduction mechanism: effective charge mobility at 70 °C was calculated to be 4.6×10−16 m2/V s: an activation energy for the conduction was estimated to be 0.81 eV at 70 °C. © 2000 American Institute of Physics.Journal of Applied Physics 05/2000; 87(10):7333-7337. · 2.17 Impact Factor -
Article: Space charge behaviour in maleic anhydride grafted polyethylene/ethylene - vinyl - acetate copolymer laminates
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ABSTRACT: Charge distributions in maleic anhydride (MAH) grafted polyethylene (g-PE)/ethylene - vinyl - acetate (EVA) copolymer laminates have been measured with materials of different composition. All laminates showed interfacial charge, the polarity and the magnitude of which are explained by interfacial polarization. It was found that the interfacial charge increased with the increase of MAH content in the g-PE, whereas it decreased with the increase of vinyl - acetate content in the EVA. This feature was attributed to the differences in electrical conductivity of the materials. Details of the experimental results are described.Journal of Physics D Applied Physics 12/1998; 30(1):1. · 2.54 Impact Factor
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Institutions
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1992–2012
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Korea University
- Department of Materials Science and Engineering
Seoul, Seoul, South Korea
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1997
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Korea Advanced Institute of Science and Technology
Seoul, Seoul, South Korea
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