Ki-Sub Kim

Korea National University of Transportation, Sŏul, Seoul, South Korea

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Publications (79)154.22 Total impact

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    Ki-Sub Kim · Byung Heung Park
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    ABSTRACT: Choline chloride (ChCl) is a well-known material forming deep eutectic solvents (DESs) when mixed with a hydrogen bonding donor (HBD). The potential applicability of DES systems is wide for replacing ionic liquids at relatively low cost. Therefore, the application to chemical processes necessitates the reliable data of DES properties. In this work, thermal behaviors of two ChCl-based DES systems (ChCl+urea and ChCl+1,3-dimethylurea) were investigated by using a differential scanning calorimeter. Crystalline as well as amorphous characteristics were found by varying compositions. In general, the increased composition of ChCl strengthened the crystallinity of solid phase. In the ChCl+urea system, a phase diagram was drawn with obtained melting point data while it could not be available for the other system.
    Preview · Article · Nov 2015 · Journal of chemical engineering of Japan

  • No preview · Article · Nov 2015 · Journal of Chemical & Engineering Data
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    ABSTRACT: Partially side-opened carbon nanopeapods show great potential for various applications. Here, we investigated the schematics and energetics of a nonvolatile nanomemory element, based on a C60 fullerene encapsulated in a partially opened carbon nanopeapod, using empirical interatomic interaction potential functions. Bistability of the van der Waals potential energy is achieved from the positional change of the encapsulated C60 fullerene, and the encapsulated C60 fullerene can shuttle between bistable positions, under alternatively applied force fields. Since the C60 fullerene can retain its position without recharging, the proposed system can operate as a nonvolatile memory device. These results can be useful for the understanding of new molecular machines.
    No preview · Article · Nov 2015 · Journal of Nanoscience and Nanotechnology
  • Yea Eun Lee · Jeong Won Kang · Ki-Sub Kim
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    ABSTRACT: Thiol-capped cadmium telluride (CdTe) nanoparticles (NPs) self-assembled into nanowires (NWs) under dark conditions, and the evolutionary process was investigated. Thiolglycolic acid (TGA) was selected as one of the stabilizers and a TGA-to-Cd ion ratio of 1.3 rather than the traditional 2.4 ratio was used. The reduced amount of the stabilizer and the oxidation of tellurium ions on CdTe NP surface under dark conditions resulted in reorganization from individual NPs into NWs consisting of multi-layers of individual NPs. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were performed to characterize the synthesized nanostructures. The NWs produced were straight and long, with lengths ranging from 500 nm to 10 μm. Photoluminescence (PL) showed that the nanostructure wavelengths were slightly blue-shifted from 546 to 539 nm. Both control of the amount of stabilizer and oxidation of Te ions acted as driving forces to form NWs. Thus, small modifications in synthesis yielded a major difference in the final nanomaterial structure. The suggested synthetic procedure provides a viable pathway for the fabrication of nanomaterials.
    No preview · Article · Oct 2015 · Journal of Nanoscience and Nanotechnology
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    ABSTRACT: Cadmium telluride (CdTe) nanowires were successfully synthesized from individual nanoparticles and the evolutionary process was investigated. Slow oxidation of Te2− in CdTe nanoparticles resulted in the generation of ribbons consisting of several layers of individual nanocrystals. The length of nanowires ranged from 1 to 8 μm. The presence of unusual shapes of multiparticle assemblies, such as bouquet, dog-bone, and ribbon bunches was observed as intermediate stages. The images of nanoribbons were analysed based on transmission electron microscopy and scanning electron microscopy. The suggested synthetic procedure provides a viable pathway for the fabrication of nanomaterials with helical conformations.
    No preview · Article · Sep 2015 · Journal of Nanoscience and Nanotechnology
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    ABSTRACT: The equilibrium boundaries of CH4 and CO2 hydrates were examined in the presence of di-carboxylic acids, glutaric acid and malonic acid, at a mass fraction of 0.1 and 0.01. Including di-carboxylic acids in the water phase shifted the phase boundaries to higher pressure and lower temperature conditions. We attributed this to the formation of hydrogen bonding between the inhibitors and water molecules rather than to the formation of water structures serving as hydrate precursors. In addition, the inhibition effect of shorter carbon-chained malonic acid was better than that of longer-chained glutaric acid due to its higher mole fraction in water phase. This inhibition effect was compared with that of conventional thermodynamic hydrate inhibitors (THIs) used in commercial processes. The comparison showed that the effect of malonic acid was close to that of tri-ethylene glycol for inhibiting the CH4 hydrate.
    No preview · Article · Sep 2015 · Fluid Phase Equilibria
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    ABSTRACT: The phase equilibrium conditions of CO2 hydrates were examined in the presence of morpholinium and piperidinium ionic liquids (ILs) with a mass fraction of 0.1. The equilibrium conditions were in the ranges of (274.6-281.2) K and (1.80-3.95) MPa. The addition of ILs shifted the hydrate equilibrium conditions to a higher pressure and lower temperature region compared to the hydrate formed from pure water. Piperidinium and morpholinium ILs showed similar inhibition effects in the higher temperature range ≥278.5K, whereas at lower temperature piperidinium ILs had a slightly better inhibition effect than morpholinium ILs. The anionic species also affected the hydrate inhibition effectiveness. Smaller anions, i.e., Br-, had a slightly better inhibition effect than the bigger ions of BF4-
    No preview · Article · Sep 2015 · Fluid Phase Equilibria
  • Oh Kuen Kwon · Ki-Sub Kim · Jeong Won Kang
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    ABSTRACT: We propose schematics for an ultra-sensitive pressure sensor based on graphene and investigate its mechanical responses using classical molecular dynamics simulations. The top structure is similar to a thumbtack or pushpin and the bottom structure is composed of the graphene on the cylindrical hole. So while the top plate applied to the actual pressure has a large area, the majority of the load transfers to the graphene through the narrow pin. Therefore, the sensitivity can be greatly enhanced and the sensing limits can be adjusted by designing the aspect ratio between the head and the pin areas composed of the top structure. Simulation results for the operations of the proposed sensor were in good agreement with the previous experimental and theoretical works. This proposed schematics can detect the pressure via the deflection change or/and the resonance frequency shift, and also have great potential for versatile applications in nanoelectromechanical systems.
    No preview · Article · Sep 2015 · Journal of Computational and Theoretical Nanoscience
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    ABSTRACT: We have investigated the motion of a C60 molecule absorbed on sinusoidal graphene nanoflake (GNF) via molecular dynamics simulations. Since C60 deposited on sinusoidal GNF is favorable on energetic grounds, the C60 molecule moved toward one of the valleys of sinusoidal GNF without energy barrier. So no sooner the C60 molecule was deposited on the sinusoidal GNF, then the C60 molecule immediately began to move toward the valley of the sinusoidal GNF. Since the position of the C60 molecule can be changed by externally applied force fields and has a binding energy of 0.754 eV in the valley of sinusoidal GNF, the sinusoidal C60/GNF can be applied to a switchable nonvolatile memory device. This work provides the probability of alternative ‘bucky shuttle’ memory based on the sinusoidal C60/GNF hybrid nanostructure.
    No preview · Article · Jul 2015 · Journal of Nanoscience and Nanotechnology
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    ABSTRACT: CdTe nanowires were synthesized from individual nanoparticles via self-assembly at a specific wavelength of light. The wavelength of 500 nm resulted in a self-assembly of nanoparticles into nanowires. Most of the produced nanowires were straight and long in shape and their length ranged from 300 nm to 20 μm. The oxidation of Te2– in CdTe nanoparticles under the visible light resulted in the assembly of nanowires consisting of several layers of individual nanoparticles. Transmission electron microscopy and scanning electron microscopy were performed to characterize the synthesized nanostructures. Energy-dispersive X-ray demonstrated the atomic percentage of nanowires. Photoluminescence showed that the wavelength of the nanostructures is slightly blue-shifted from 555 to 548 nm.
    No preview · Article · Jul 2015 · Journal of Nanoscience and Nanotechnology
  • Jeong Won Kang · Ki-Sub Kim · Oh Kuen Kwon
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    ABSTRACT: This paper presents the schematics and the energetics of nonvolatile-nanomemory-element based on carbon nanotube (CNT) on graphene nanoribbon (GNR) array using interatomic interaction potential function. The system proposed was composed of short outer CNT and long core CNT placed on two GNRs with a gap. The short outer CNT, which can be formed by electro-burning or electron-beam stripping, shuttles between two GNRs along the core CNT under the alternatively applied force fields. When the outer CNT settles on the GNRs, the local energy minima are achieved from the attractive van der Waals potential energies and then, since the outer CNT shuttle remains its position on the GNR without external force fields, the proposed system can operate a nonvolatile memory device. To switch this CNT shuttle system, the external force fields to overcome the restoring force exerted by van der Waals attractions should be applied.
    No preview · Article · Mar 2015 · Journal of Computational and Theoretical Nanoscience
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    ABSTRACT: We address the simple schematics of graphene-nanoflake shuttle-memory and investigate its energetic and dynamic properties. The internal dynamics of a related model system, consisting of a graphene-nanoflake on a patterned graphene nanoribbon, are investigated via classical molecular dynamics simulations. The van der Waals interactions between the graphene-nanoflake and the patterned graphene nanoribon make bistable potential energy wells in the larger surface area regions of the patterned graphene nanoribbon, and then the graphene-flake keeps its seat on one of the bistable positions, which is the place where the binary data is archived. This graphenenanoflake shuttle can be a tunable two-level system, where transitions between the bistable positions can be induced by applying an electric field. Nanostructures composed of graphene-nanoflake on graphene-nanoribbon are applicable to ultra-fast response oscillators, switches, sensors, and quantum computing, as well as nonvolatile memory.
    No preview · Article · Jan 2015 · Journal of Computational and Theoretical Nanoscience

  • No preview · Article · Dec 2014
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    ABSTRACT: Ionic liquids (ILs) have been proposed as potential inhibitors for preventing gas hydrate formation because their ion pairs effectively interrupt the hydrogen bonding between water molecules. ILs also have broad inhibitory capabilities depending on the specific cation and anion combinations. The final structural design of ILs for hydrate inhibition must be performed after an inhibition mechanism is suggested. In this study, the inhibitory thermodynamic effects of ILs were measured by the hydrate–aqueous liquid–liquid carbon dioxide (CO2) equilibrium, and the experimental results were analyzed based on the hydration free energy of ILs calculated through molecular dynamics study. 1-Hydroxyethyl-1-methylpyrrolidinum chloride showed the best inhibitory performance of the suggested candidates. The anions mostly contributed to the thermodynamic inhibition, but the cations had a marginal impact on CO2 hydrate inhibition. Through fundamental understanding of the inhibition mechanism by both experimental and computational approaches, it is highly possible to provide crucial information for effective ILs to be designed as the CO2 hydrate inhibitor.
    Full-text · Article · Nov 2014 · Fluid Phase Equilibria
  • Ki Sun Lee · Jeong Won Kang · Jong-Ho Cha · Ki-Sub Kim
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    ABSTRACT: Cadmium telluride (CdTe) nanowires were successfully synthesized from individual nanoparticles via self-assembly, and the evolutionary process was investigated. The oxidation of tellurium ions in CdTe nanoparticles under dark conditions led to the assembly of straight nanowires made of several layers of individual nanoparticles. Transmission electron microscopy and scanning electron microscopy were performed to characterize the synthesized nanostructures. The length of the NWs assembled from CdTe NPs ranged from 0.5 to 30 μm. Unlike generally prepared NWs, these NWs were made from individual NPs layered on top of each other. Remarkably, the assembly of individual NPs formed bundles during the intermediate steps before they unraveled into individual NWs. Both control of the amount of stabilizer and oxidation of Te ions acted as driving forces to form NWs. Thus, small modifications in synthesis yielded a major difference in the final nanomaterial structure. The suggested synthetic procedure provides a viable pathway for the fabrication of nanomaterials.
    No preview · Article · Nov 2014 · Journal of Nanoscience and Nanotechnology
  • Yong Hwa Lee · Woo Youn Lee · Ki-Sub Kim · Yeon Ki Hong
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    ABSTRACT: As an effective method for extraction of acrylic acid, aqueous two-phase systems based on morpholinium ionic liquids were used in this study. Effects of the alkyl chain length of cation in morpholinium ionic liquids on phase diagram and extraction efficiencies were investigated. Experimental results show that aqueous two phase systems can be formed by adding appropriate amount of morpholinium ionic liquids to aqueous K2HPO4 solutions. It can be found that the ability of morpholinium ionic liquids for phase separation followed the order [HMMor][Br] > [OMMor][Br] > [BMMor][Br> [EMMor][Br]. There was little difference between binodal curves of imidazolium ionic liquids and those of morpholinium ionic liquids. 50∼90% of the extraction efficiency was observed for acrylic acid by aqueous two phase extraction of acrylic acid with morpholinium ionic liquids. It can be concluded that morpholinium ionic liquids/K2HPO4 were effective for aqueous two phases extraction of acrylic acid comparing to imidazolium ionic liquids/K2HPO4 systems because of their lower cost.
    No preview · Article · Oct 2014 · Korean Chemical Engineering Research
  • Ki-Sub Kim · Byung Heung Park

    No preview · Article · Sep 2014
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    ABSTRACT: We report the concept of combining ionic liquids (ILs) with polymer inhibitors to more effectively inhibit methane hydrate formation. The new inhibitors extended the induction time and decreased the growth rate of the hydrate. It was found that the presence of a hydroxyl group on IL provided the most powerful inhibition effect by forming hydrogen bonds between IL and water molecules.
    No preview · Article · Nov 2013 · RSC Advances
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    ABSTRACT: We investigated the phase equilibrium boundary of tri-n-butylphosphine oxide (TBPO) semiclathrate hydrates incorporated with CH4, CO2, and H2. TBPO aqueous solutions with a molality (m) of (1.61 and 1.98) mol·kg–1 were used for hydrate formation, which corresponded to the clathrate structures of TBPO·34.5H2O and 28H2O, respectively. The phase boundary at both concentrations was shifted to the promotion region represented by lower pressures and higher temperatures, compared to each simple gas hydrate. In particular, TBPO + CO2 double hydrate presented mild hydrate stabilization conditions of <1 MPa at (280 to 285) K. Additionally, the dissociation enthalpy (ΔHd) calculated from the phase boundary curves for the TBPO + CO2 double hydrates was almost the same as that for tetra-n-butylammonium bromide (TBAB) + CO2 double hydrate (219.5 kJ·mol–1 for m = 1.61 mol·kg–1 and 211.6 kJ·mol–1 for m = 1.98 mol·kg–1). These results demonstrate that the TBPO + CO2 double hydrate could be used as refrigerants for cold storage and transportation.
    No preview · Article · Nov 2013 · Journal of Chemical & Engineering Data
  • Ki-Sub Kim · Zion Hwang · Jeong Won Kang
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    ABSTRACT: We investigate the dynamics behaviors of single-layered graphene sheet resonator at constant temperature via classical molecular dynamics simulations. The simulation results show that the graphene sheet resonator works in a mixed behavior, partly chaotic and partly regular, which is due to the interaction between the self-rippling of the graphene sheet and the applied gate forces. However in spite of the partial chaotic motions, the existence of regular signature can allow the development of tunable resonators. Hence the resonance frequencies as a function of the applied fate force can be regressed by the power function, this result shows the tenability of the graphene sheet resonator by controlling electrical direct current bias of the gate. Graphene resonators as ultra-sensitive sensors can be well-modeled using the tension variations induced by the applied gate force.
    No preview · Article · Aug 2013 · Journal of Computational and Theoretical Nanoscience

Publication Stats

1k Citations
154.22 Total Impact Points

Institutions

  • 2012-2015
    • Korea National University of Transportation
      • Department of Chemical and Biology Engineering
      Sŏul, Seoul, South Korea
  • 2009-2015
    • Chungbuk National University
      • Department of Chemical Engineering
      Chinsen, Chungcheongbuk-do, South Korea
  • 2001-2007
    • Korea Advanced Institute of Science and Technology
      • Department of Chemical and Biomolecular Engineering
      Seoul, Seoul, South Korea