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Lee, Jun‐,Ho,Lee, Youngkwan,Nam, Jae‐,Do John Wiley Sons, Ltd. 2010 Surface and interface analysis Vol.42 No.1
<P><B>Abstract</B></P><P>We investigated the delamination problem at the metal‐polymer interface and the mechanical buckling of the metal layer at a localized area of the metallic shell under compression between two parallel plates. First, polystyrene (PS) beads were synthesized by dispersion polymerization and then their sulfonation process. After sequential electroless deposition, the average size of multi‐metal coated sulfonated polystyrene (SPS) bead was <I>ca</I> 4.95 µm. Using the electromechanical indentation, the electrical resistance of a single metal‐coated SPS bead decreased with increasing compressive strain without delamination at the metal‐polymer interface, and its electrical resistance showed 5.65 Ω. Copyright © 2009 John Wiley & Sons, Ltd.</P>
Lee, Sang Ha,Lee, Hyuck,Cho, Misuk,Lee, Youngkwan Elsevier 2017 Carbon Vol.115 No.-
<P>Here, we introduce a layered hollow sphere (LHS) architecture of iridium -decorated carbon electrode. The electrode was prepared by coating of a solution composed of graphene oxide (GO), IrC1(3), and polystyrene bead followed by subsequent pyrolysis. The morphology of the electrode was investigated according to the composition of solution, and the electrocatalytic properties were characterized. The usage of GO highly enhanced the electrochemical surface area of the electrode (by similar to 6 times). The LHS electrode also showed outstanding electrocatalytic properties: a current density of 89.99 mA/cm(2) could be obtained at a potential of 1.6 V. (C)2017 Elsevier Ltd. All rights reserved.</P>
Lee, Seokjae,Koo, Jaryong,Hyung, Gunwoo,Lim, Donghwan,Lee, Donghyung,Lee, Kumhee,Yoon, Seungsoo,Kim, Wooyoung,Kim, Youngkwan Springer 2012 Nanoscale research letters Vol.7 No.1
<P>We investigate multiple quantum well [MQW] structures with charge control layers [CCLs] to produce highly efficient blue phosphorescent organic light-emitting diodes [PHOLEDs]. Four types of devices from one to four quantum wells are fabricated following the number of CCLs which are mixed p- and n-type materials, maintaining the thickness of the emitting layer [EML]. Remarkably, such PHOLED with an optimized triplet MQW structure achieves maximum luminous and external quantum efficiency values of 19.95 cd/A and 10.05%, respectively. We attribute this improvement to the efficient triplet exciton confinement effect and the suppression of triplet-triplet annihilation which occurs within each EML. It also shows a reduction in the turn-on voltage from 3.5 V (reference device) to 2.5 V by the bipolar property of the CCLs.</P>
Lee, Sangyool,Cho, Mi-Suk,Nam, Jae-Do,Lee, Youngkwan American Scientific Publishers 2008 Journal of nanoscience and nanotechnology Vol.8 No.10
<P>Arrays of polypyrrole nanorods were fabricated using an anodized aluminum oxide (AAO) template for use as supercapacitors. Gold was deposited on one side of the AAO template by thermoevaporation for use as an electrode and pyrrole was electrochemically polymerized, causing it to grow from the gold electrode into the AAO template. The length of the PPy nanorods was controlled by adjusting the applied charge, and nanorods with three different lengths were prepared: 1.2 microm for 0.5 C x cm(-2), 2.4 microm for 1.0 C x cm(-2), and 4.6 microm for 2.0 C x cm(-2). After the removal of the AAO template in alkali solution, a well-arranged polypyrrole (PPy) nanorod electrode structure having an extremely large surface area was produced. The morphology of the PPy nanorods was monitored by SEM. The capacitive performances of the PPy nanorod array electrodes were investigated by cyclic voltammetry (CV) as well as the galvanostatic charge/discharge test. Greatly enhanced capacity performance was observed in the nanorod electrodes. Also, a higher specific capacitance was observed in the longer nanorod electrode having a larger surface area.</P>
Crosslinked Gel Polymer Electrolytes for Si Anodes in Li-Ion Batteries
Lee, Jeong Hun,Kim, Soochan,Cho, Misuk,Chanthad, Chalathorn,Lee, Youngkwan The Electrochemical Society 2019 Journal of the Electrochemical Society Vol.166 No.13
<P>Gel polymer electrolyte (GPE) membrane was prepared by the facile amine-epoxy crosslinking reaction of poly(ethylene glycol)diglycidylether (PEGDE) with diamino-poly(propylene oxide) (DPPO) and subsequent immersion in 1 M LiPF<SUB>6</SUB> solution. To apply GPE for Si anode in a Li-ion battery, the physical properties were optimized by the degree of crosslinking which was controlled by molecular weight of each part. The crosslinked GPE membrane composed of PEGDE(1,000 g mol<SUP>−1</SUP>) and DPPO (4,000 g mol<SUP>−1</SUP>) exhibited desirable dimensional stability, low electrical resistance, adequate ionic conductivity of 1.0 mS cm<SUP>−1</SUP> at 25°C. The Si anode cell employing this GPE exhibited enhanced battery performance of 2,434 mAhg<SUP>−1</SUP> and 80% cyclic retention after 100 cycles. The well-optimized cGPE with desirable physical properties could resolve the issues of safety and stability resulted from volume expansion of Si as well as Li dendrite formation.</P>
Effect of ZnO particle sizes on thermal aging behavior of natural rubber vulcanizates
Lee, Yong Hwan,Cho, Misuk,Nam, Jae-Do,Lee, Youngkwan Elsevier 2018 Polymer degradation and stability Vol.148 No.-
<P><B>Abstract</B></P> <P>The effects of ZnO particle size on crosslinking and thermal aging behavior of natural rubber (NR) were investigated. NR vulcanizates filled with nano ZnO allowed higher crosslink density, lower polysulfide crosslink, and stronger mechanical properties than those filled with micro ZnO. After thermal aging, NR filled with nano ZnO exhibited much more stable chemical and mechanical properties. The high crosslink density as well as the formation of more stable mono- and di-sulfidic crosslinks was attributed to the good dispersion and high surface area of the nano ZnO.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effects of ZnO particle size on crosslinking and thermal aging of natural rubber (NR) were investigated. </LI> <LI> High crosslink density as well as the formation of more stable crosslinks was attributed to high surface area of nano ZnO. </LI> <LI> NR vulcanizates with nano ZnO exhibited high retention of mechanical properties after thermal aging. </LI> </UL> </P>