Wonsang Koh
Georgia Institute of Technology
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Featured researches published by Wonsang Koh.
ACS Applied Materials & Interfaces | 2011
Wonsang Koh; Ji Il Choi; Kevin Donaher; Seung Geol Lee; Seung Soon Jang
The lithium (Li) adsorption mechanism on the metallic (5,5) single wall carbon nanotube (SWCNT)-fullerene (C(60)) hybrid material system is investigated using first-principles method. It is found that the Li adsorption energy (-2.649 eV) on the CNT-C(60) hybrid system is lower than that on the peapod system (-1.837 eV) and the bare CNT (-1.720 eV), indicating that the Li adsorption on the CNT-C(60) hybrid system is more stable than on the peapod or bare CNT system. This is due to the C(60) of high electron affinity and the charge redistribution after mixing CNT with C(60). In order to estimate how efficiently Li can utilize the vast surface area of the hybrid system for increasing energy density, the Li adsorption energy is calculated as a function of the adsorption positions around the CNT-C(60) hybrid system. It turns out that Li preferably occupies the mid-space between C(60) and CNT and then wraps up the C(60) side and subsequently the CNT side. It is also found that the electronic properties of the CNT-C(60) system, such as band structure, molecular orbital, and charge distribution, are influenced by the Li adsorption as a function of the number of Li atoms. From the results, it is expected that the CNT-C(60) hybrid system has enhanced the charge transport properties in addition to the Li adsorption, compared to both CNT and C(60).
ChemPhysChem | 2015
Wonsang Koh; Hye Sook Moon; Seung Geol Lee; Ji Ii Choi; Seung Soon Jang
The mechanism of Li adsorption on a graphene-fullerene (graphene-C60 ) hybrid system has been investigated using density functional theory (DFT). The adsorption energy for Li atoms on the graphene-C60 hybrid system (-2.285 eV) is found to be higher than that on bare graphene (-1.375 eV), indicating that the Li adsorption on the former system is more stable than on the latter. This is attributed to the high affinity of Li atoms to C60 and the charge redistribution that occurs after graphene is mixed with C60 . The electronic properties of the graphene-C60 system such as band structure, density of states, and charge distribution have been characterized as a function of the number of Li atoms adsorbed in comparison to those of the pure graphene and C60 . Li adsorption is found to preferentially occur on the C60 side due to the high adsorption energy of Li on C60 , which imparts a metallic character to the C60 in the graphene-C60 hybrid system.
RSC Advances | 2015
Wonsang Koh; Ji Hye Lee; Seung Geol Lee; Ji Il Choi; Seung Soon Jang
In this study, we investigated the mechanisms of Li adsorption on a graphene–C60 nanobud system using density functional theory. Li adsorption on the hybrid system was enhanced compared to those using pure graphene and C60. The Li adsorption energies ranged from −1.784 to −2.346 eV for the adsorption of a single Li atom, and from −1.905 to −2.229 eV for the adsorption of two Li atoms. Furthermore, adsorption energies were similar at most positions throughout the structure. The Li adsorption energy of an 18-Li adsorbed system was calculated to be −1.684 eV, which is significantly lower than Li–Li binding energy (−1.030 eV). These results suggest that Li atoms will be adsorbed preferentially (1) between C60 and C60, (2) between graphene and C60, (3) on graphene, or (4) on C60, rather than form Li clusters. As more Li atoms were adsorbed onto the graphene–C60 nanobud system because of its improved Li adsorption capability, the metallic character of the system was enhanced, which was confirmed via analysis of band structure and electronic density of states.
IEEE Transactions on Components, Packaging and Manufacturing Technology | 2011
Seung Geol Lee; Ji Il Choi; Wonsang Koh; Seung Soon Jang; Jongman Kim; Gene Kim
The effect of temperature on the distribution and transport of water molecules in a model epoxy molding compound (EMC) system is investigated using atomistic molecular dynamics simulation with 4 and 7 wt% water content at various temperatures, such as 298, 323, 353, and 373 K. The thermal expansion of the hydrated model EMC was evaluated as 1-5% of its dried volume with increasing temperature. The spatial distributions of the amine groups and hydroxyl groups are not significantly affected by temperature due to the crosslinked topological constraint. The correlation of these functional groups with water molecules was not affected by temperature due to their hydrophilicity. In contrast, it is observed that the water phase is expanded with increasing temperature, which is more distinct as a function of water content. The temperature effect on the water diffusion was clearly observed: the diffusion coefficient became larger with increasing temperature. The activation energy for the water diffusion via a hopping mechanism was 21.9 kJ/mol (0.23 eV) and 21.2 kJ/mol (0.22 eV) for the 4 wt% and the 7 wt% water contents, respectively, which infers that the water transport is more facilitated with increasing water content because the water structure of the water phase in the model EMC is more developed.
Carbon | 2011
Wonsang Koh; Ji I. Choi; Seung G. Lee; Wang R. Lee; Seung Soon Jang
Applied Clay Science | 2013
Seung Geol Lee; Ji Il Choi; Wonsang Koh; Seung Soon Jang
Journal of Physical Chemistry C | 2012
Seung Geol Lee; Tod A. Pascal; Wonsang Koh; Giuseppe F. Brunello; William A. Goddard; Seung Soon Jang
Current Applied Physics | 2014
Wonsang Koh; Ji Ii Choi; Euigyung Jeong; Seung Geol Lee; Seung Soon Jang
Theoretical Chemistry Accounts | 2012
Seung G. Lee; Wonsang Koh; Giuseppe F. Brunello; Ji Il Choi; David G. Bucknall; Seung Soon Jang
Archive | 2010
Kevin Donaher; Seung Soon Jang; Wonsang Koh