Ki-Sub Kim

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

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Publications (30)41.92 Total impact

  • [Show abstract] [Hide abstract]
    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.
    RSC Advances 11/2013; 3(43):19920-19923. · 2.56 Impact Factor
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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.
    Journal of Chemical & Engineering Data 11/2013; 58(12):3494–3498. · 2.00 Impact Factor
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    ABSTRACT: A tunable graphene-resonator was investigated using classical molecular dynamics modeling and simulations. The fundamental resonance frequency variation of the graphene resonator was found to be very closely related to the average tension acting on both its edges. The initial stain-induced tension could be adjusted by using the mismatch between the negative thermal expansion coefficient of the graphene and the positive thermal expansion coefficient of the substrate, and the deflection-induced tension could be controlled by an electrostatic capacitive force due to the gate voltage. For very small initial axial-strains, the tunable range reached above several hundred gigahertz. As the initial axial-strain on the graphene-resonator increased, both the tunability and the tunable range decreased. The fundamental resonance frequency as a function of the calculated gate voltage was in good agreement with previous experiments. Considering the variables that affect the tension variation, this graphene-resonator is suitable for use as an ultra-sensitive accelerometer, thermo-sensor or weight scale, as well as many other types of sensor.
    Current Applied Physics 06/2013; 13(4):789–794. · 1.81 Impact Factor
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    ABSTRACT: We presented simple schematics of a nanoscale inertial measurement unit based on the self-retraction motion of the graphene flakes. When an external force is applied to the nanoscale graphite flake, the inertial force exerted on the movable layer can telescope it, then the self-restoring force also arises as the van der Waals force between the interlayers of the flake, which each suspended flake can automatically and fully retract back onto the top of the graphite platform immediately after the externally applied force is released. Since the van der Waals force linearly increases with the increasing size of the flake, the sensing limitation can be controlled. When the external force does not exceed the retracting force, this addressed nanoscale inertial measurement unit can be semi-permanently used. Therefore, the size and the thickness of the graphene flake should be carefully selected with a tradeoff. These graphite flakes can be utilized as a basic structure in various nanoelectromechanical devices, such as switch and memory, linear and angular accelerometers, and pressure sensors.
    Physica E Low-dimensional Systems and Nanostructures 05/2013; 50:44–50. · 1.52 Impact Factor
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    ABSTRACT: A tunable graphene-nanoribbon (GNR)-resonator was investigated via classical molecular dynamics simulations. Resonance frequencies increased with increasing externally applied gate-force and axial-strain, and could be tuned above several hundred GHz. Tunable resonance frequencies achieved from the gate force were higher than those achieved from the axial-strain. The operating frequencies of GNR-resonators without axial-strain or with small axial-strains were most widely tuned by the gate, and almost linearly increased with increasing mean deflection. As the axial strain increased, the tunable ranges of the GNR-resonators were exponentially decreased, although the operating frequencies increased. GNR-resonators without axial-strain could be applied to wide-range-tuners, whereas GNR-resonators with high axial-strain could be applied to high-frequency-fine-tuners.
    Current Applied Physics 03/2013; 13(2):360–365. · 1.81 Impact Factor
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    ABSTRACT: We propose schematics for an ultra-sensitive pressure sensor based on graphene-nanoribbon (GNR) and investigate its electromechanical properties using classical molecular dynamics simulations and piezo-electricity theory. Since the top plate applied to the actual pressure is large whereas the contact area on the GNR is very small, both the sensitivity and the sensing range can be adjusted by controlling the aspect ratio between the top plate and the contact point areas. Our calculation shows that the electrical conductivity of GNRs can be tuned by the applied pressure and the electric conductance of the deflected GNR linearly increases with increasing applied pressure for the linear elastic region in low pressure below the cut-off point. In the curves for both the deflection and potential energy, the linear elastic regime in low pressure was explicitly separated with the non-linear elastic regime in high pressure. The proposed GNR-based nanoelectromechanical devices have great potential for application as electromechanical memory, relay or switching devices.
    Physica E Low-dimensional Systems and Nanostructures 01/2013; 47:6–11. · 1.52 Impact Factor
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    ABSTRACT: We investigated an ultrahigh sensitive accelerometer based on graphene nanoribbon resonators. Sensing acceleration can be made by their resonance frequency shift and/or their capacitance change. Schematics and the static properties were introduced and the dynamic properties were investigated via classical molecular dynamics simulation. As the acceleration increased, the oscillations of the deflections were going dramatically faster and the mean deflections increased, then the capacitance continually varied with large amplitudes and the resonance frequencies linearly increased in a log–log scale by power regression. The energy loss decreased with increasing time, and the average quality factors were dramatically reduced with increasing acceleration.
    Physics Letters A 10/2012; 376(45):3248–3255. · 1.77 Impact Factor
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    ABSTRACT: We investigated the dynamics properties of the carbon-nanotube (CNT) oscillators with intertube gaps via classical molecular dynamics simulations. The maximum frequencies of the CNT-oscillators were achieved when the lengths of the outertube including the gap were the same as the length of the coretube, and so their maximum frequencies, with the same coretube length, were the same as each other regardless of the gap's value. Their resonance frequencies were complexly correlated with the geometric parameters and initial conditions such as initial velocity and displacement. Increasing the outertube's length by increasing the gap was the most important parameter in estimating the resonance frequency of the CNT-oscillator with an intertube gap between outertubes. Finally, we note that CNT-oscillators with intertube gaps can be applied as frequency-controlled oscillators by manipulating this gap.
    Physica E Low-dimensional Systems and Nanostructures 07/2012; 44(10):2027–2031. · 1.52 Impact Factor
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    ABSTRACT: In this paper, we investigated the resonant frequencies of multi-walled carbon nanotube (MWCNT) resonators with short outertubes according to the classical molecular dynamics approach. The resonant frequencies of the MWCNT resonators with short outertubes were influenced in both the wall number and the length of the short outertubes. The resonance frequencies of MWCNTs with short outertubes could be modeled by Gaussian distribution functions. Both the bandwidth and the sensitivity increased with increasing the wall number of the outertubes. The maximum frequency increased with increasing the diameter and with increasing the wall number of the outertubes for MWCNTs. So the effects of increasing the wall number of the outertubes were very important factors for understanding the vibrational frequency changes of MWCNTs with short outertubes as well as the effect of increasing the lengths of the outertubes.
    Journal of Nanoscience and Nanotechnology 05/2012; 12(5):4224-7. · 1.15 Impact Factor
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    ABSTRACT: CdTe nanorribons were successfully synthesized from individual nanoparticle. Slow oxidation of Te(2-) in CdTe nanoparticles resulted in the assembly of ribbons consisting of several layers of individual nanocrystals. The light-controlled self-assembly of CdTe nanoparticles led to twisted ribbons with variable pitch. Transmission electron microscopy, scanning electron microscopy, and atomic force microscopy were performed to characterize the synthesized nanostructures. The suggested synthetic procedure provides a viable pathway for the fabrication of nanomaterials with helical conformations.
    Journal of Nanoscience and Nanotechnology 05/2012; 12(5):4309-12. · 1.15 Impact Factor
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    ABSTRACT: We have successfully synthesized ionic liquid (IL)-stabilized palladium (Pd) nanoparticles (NPs) by electrochemical reduction. The particle size was controlled by adjusting the current density. Transmission electron microscopic (TEM) images showed that the average diameters of the Pd NPs were 2.4, 3.2, and 3.5 nm, depending on the synthetic conditions. Particle size increased as the current density and the length of the alkyl chain in the cation decreased. X-ray diffraction of the resulting NPs indicated that the particles had a crystalline structure. Overall, the results show that NPs can be finely tuned according to the kinds of ILs employed, as well as by electrochemical reduction.
    Journal of Nanoscience and Nanotechnology 04/2012; 12(4):3641-5. · 1.15 Impact Factor
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    ABSTRACT: CdTe nanoribbons feature their unique optical properties compared with CdTe nanoparticles. Slow oxidation of tellurium ions on CdTe nanoparticles resulted in the organization of individual nanoparticle into nanoribbons. The light-controlled self-assembly of CdTe nanoparticles led to twisted ribbons. It was found that irradiation improved the oxidation of tellurium ions. Transmission electron microscopy (TEM) were performed to characterize the synthesized nanostructures and showed nanowires were twisted after self-assembly. The photoluminescence was slightly blue-shifted from 550 to 544 nm. This synthetic procedure could potentially provide a key step toward the fabrication of nanowires.
    Korean Chemical Engineering Research. 01/2012; 50(6).
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    ABSTRACT: In this paper, we investigated cantilevered carbon-nanotube-resonators encapsulating finite nanoclusters with different linear-densities via classical molecular dynamics simulations, which included the use of the approximation model. Through this we can simply obtain the fundamental frequency shifts of the cantilevered carbon-nanotube-resonators encapsulating finite nanoclusters. As the linear mass density of the encapsulated finite nanocluster increased, the frequency-shift-range also increased. Previous works focused on the resonance-frequency-shift due to the attached mass but our molecular dynamics simulation looked into the dependence on the linear density of the encapsulated nanocluster as an important parameter to analyze the vibration features of carbon-nanotube-resonators. The molecular dynamics simulation results were in good agreement with those of previously related experimental and theoretical works.
    Physica E Low-dimensional Systems and Nanostructures 01/2012; 44(s 7–8):1543–1547. · 1.52 Impact Factor
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    ABSTRACT: We investigate the nano mass transfer in an ultrahigh frequency carbon-nanotube-resonator encapsulating a nanocluster via classical molecular dynamics simulations. When the carbon-nanotube-resonator vibrated, the encapsulated copper nanocluster more rapidly approached the end of the cantilevered carbon-nanotube-resonator. Such phenomena were due to the migration of the encapsulated copper nanocluster due to the centrifugal force induced by the vibrating nanotube resonator. So the resonance frequency change could be time-dependently found. For the movable copper nanocluster in carbon nanotube resonator, the vibrational spectra when the copper nanocluster inside the carbon nanotube resonator rapidly settled at the capped edge were different from those obtained when the copper nanocluster continuously oscillated inside the carbon nanotube resonator. Such results showed that the frequency of the carbon-nanotube-resonator encapsulating the movable copper nanocluster could be adjusted by controlling the mean position of the oscillating copper nanocluster. The movable nanocluster inside a carbon-nanotube can be applied to a nanotube-based data storage media by sensing the position of the nanocluster.
    Journal of Nanoscience and Nanotechnology 07/2011; 11(7):5856-60. · 1.15 Impact Factor
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    ABSTRACT: We conceptually investigated a carbon-nanotube-based tuner operated by the telescoping nanotube motion in a multi-walled carbon-nanotube induced by electromigration of an encapsulated nanoparticle. The telescoping lengths in the proposed carbon-nanotube-based tuner could be achieved from the electromigration phenomena of the nanoparticle embedded in the carbon nanotube. So the core part is the nanoparticle shuttle and a multi-walled carbon-nanotube with ultra-low interlayer friction. The tuning of this telescoping carbon-nanotube-based tuner is achieved from the electric current flow. The properties of operation were investigated via classical molecular dynamics simulations and then the parameters of the continuum model were then calibrated to fit the results of the molecular dynamics simulations. Since the effective boundary considered as the movable clamp affected the vibration of the telescoping nanotube, the calibrated Young's modulus of this work were lower than the those of the previous works. Presented tuners are controllable in a few nanometers, and their operations are robust and reliable.
    Journal of Nanoscience and Nanotechnology 07/2011; 11(7):6359-63. · 1.15 Impact Factor
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    ABSTRACT: Pyrrolidinium cation-based ionic liquids were synthesized, and their inhibition effects on methane hydrate formation were investigated. It was found that the ionic liquids shifted the hydrate equilibrium line to a lower temperature at a specific pressure, while simultaneously delaying gas hydrate formation.
    Chemical Communications 06/2011; 47(22):6341-3. · 6.38 Impact Factor
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    ABSTRACT: We investigated, via the classical MD simulation method based on Tersoff–Brenner potential, the fundamental resonance frequency changes of single-walled carbon nanotube (SWCNT) resonators originated from the purely mechanical coupling of the axial-strain-induced torsion (ASIT) response. The fundamental frequency changes were also negligible where the ASIT responses were negligible in achiral SWCNTs whereas those were explicitly found under both compression and tension for the chiral SWCNTs with the obvious ASIT responses. Specially, for SWCNT with the chiral angle of π/12π/12, where the highest ASIT response can be found, the fundamental resonance frequency changes were highest. The fundamental resonance frequencies under the tensioning increased almost linearly with increasing the axial strain whereas they rapidly decreased under compression with increasing the compressive strain.
    Physics Letters A 03/2011; 375(12):1470–1476. · 1.77 Impact Factor
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    ABSTRACT: We investigated a linear nanomotor based on the telescoping carbon nanotube motion induced by electromigration of an encapsulated nanoparticle. The nanoparticle motion induced by the electric current makes the inner nanotube linearly telescope or retreat. Theoretical results using a kinetic Monte Carlo method were in good agreement with previous experiments. The telescoping speed of the linear nanomotor exponentially decreased with increasing mass of the inner nanotube.
    Journal of Nanoscience and Nanotechnology 02/2011; 11(2):1573-6. · 1.15 Impact Factor
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    ABSTRACT: We investigated the cantilevered carbon-nanotube-resonator including electromigratively movable nanoparticle via classical molecular dynamics simulations and continuum model. The change of the effective mass value, which was closely correlated with the position change of the encapsulated nanoparticle, could be regressed by a power function, the resonance frequency of the carbon-nanotube-resonator could be tuned by controlling the nanoparticle’s position, and the possible frequency-shift-ranges then reached 18–85%. The suggested device could be served as a data-storage-media for electromechanical nonvolatile-memory as well as a frequency-tuner.Research highlights► Cantilevered carbon-nanotube-resonator including electromigratively movable nanoparticle. ► Resonance frequency can be tuned by controlling the nanoparticle’s position. ► Suggested device can be served as an electromechanical nonvolatile-memory.
    Computational Materials Science. 01/2011; 50(5):1818-1822.
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    ABSTRACT: We investigated an ultrahigh frequency carbon nanotube resonator encapsulating a nanocluster, as another tunable resonator, via classical molecular dynamics simulations and continuum models. The fundamental frequency of cantilevered carbon nanotube resonator encapsulating a copper nanocluster could be adjusted by controlling the position of the encapsulated copper nanocluster. Data obtained from the molecular dynamics simulations were analyzed with continuum theory, and we found that statistically the change in the effective mass factor was greatly correlated with the position change of the encapsulated nanocluster.Research Highlights► Fundamental frequency of cantilevered carbon nanotube resonator encapsulating a copper nanocluster can be adjusted by controlling the position of the encapsulated copper nanocluster. ► Data obtained from the molecular dynamics simulations were analyzed with continuum theory. ► Statistically, the change in the effective mass factor was greatly correlated with the position change of the encapsulated nanocluster.
    Physica E Low-dimensional Systems and Nanostructures 01/2011; 43(4):909-913. · 1.52 Impact Factor

Publication Stats

39 Citations
41.92 Total Impact Points

Institutions

  • 2012–2013
    • Korea National University of Transportation
      • Department of Chemical and Biology Engineering
      Sŏul, Seoul, South Korea
    • Semyung University
      • Department of Electronic Engineering
      Cheongsong gun, North Gyeongsang, South Korea
    • Virginia Polytechnic Institute and State University
      Blacksburg, Virginia, United States