Gunyeop Park

Self-assembled foam-like graphene networks formed through nucleate boiling

Self-assembled foam-like graphene (SFG) structures were formed using a simple nucleate boiling method, which is governed by the dynamics of bubble generation and departure in the graphene colloid solution. The conductivity and sheet resistance of the calcined (400°C) SFG film were 11.8 S·cm–1 and 91.2 Ω□−1, respectively, and were comparable to those of graphene obtained by chemical vapor deposition (CVD) (~10 S·cm–1). The SFG structures can be directly formed on any substrate, including transparent conductive oxide (TCO) glasses, metals, bare glasses, and flexible polymers. As a potential application, SFG formed on fluorine-doped tin oxide (FTO) exhibited a slightly better overall efficiency (3.6%) than a conventional gold electrode (3.4%) as a cathode of quantum dot sensitized solar cells (QDSSCs).

Wicking and spreading of water droplets on nanotubes.

Recently, there has been intensive research on the use of nanotechnology to improve the wettability of solid surfaces. It is well-known that nanostructures can improve the wettability of a surface, and this is a very important safety consideration in regard to the occurrence of boiling crises during two-phase heat transfer, especially in the operation of nuclear power plant systems. Accordingly, there is considerable interest in wetting phenomena on nanostructures in the field of nuclear heat transfer. Much of the latest research on liquid absorption on a surface with nanostructures indicates that liquid spreading is generated by capillary wicking. However, there has been comparatively little research on how capillary forces affect liquid spreading on a surface with nanotubes. In this paper, we present a visualization of liquid spreading on a zircaloy surface with nanotubes, and establish a simple quantitative method for measuring the amount of water absorbed by the nanotubes. We successfully describe liquid spreading on a two-dimensional surface via one-dimensional analysis. As a result, we are able to postulate a relationship between liquid spreading and capillary wicking in the nanotubes.

Nonlocal electron electrodynamics in high-frequency capacitive discharges

Several nonlocal electron behaviors in low-pressure high-frequency capacitive discharges were found through particle-in-cell/Monte Carlo simulations. First, a negative power deposition region becomes wider as the rf frequency decreases. Second, in the spatial profile of the amplitude of the rf electric field, a nonmonotonic structure appears at the bulk-sheath boundary along with an abrupt change in the phase of the rf electric field. Third, in the spatial profile of the amplitude of the rf electron current, the second peak appears in the bulk.

Reaction rate of Na-based titanium nanofluid with water

Suppression of chemical reactivity in reaction between sodium (Na) and water by Na-based titanium nanofluid (NaTiNF) was verified by measuring the difference between the H2 generation rates of NaTiNF–water reaction and sodium–water reaction (SWR). H2 generation at the beginning of the reaction was slower in NaTiNF–water reaction than in SWR. To determine the effect of temperature on the reaction rate, NaTiNF–water reactions were conducted at 104 °C, 120 °C and 150 °C. At 104 °C, the reaction rate of SWR was twice as fast as NaTiNF–water reaction. This result demonstrates that the chemical reactivity of liquid Na is suppressed by the presence of Ti nanoparticles in liquid Na. The reaction rate of NaTiNF–water reaction increased with reaction temperature. The activation energy of NaTiNF–water reaction was obtained using the Arrhenius equation.

Nonlocal Electron Kinetics in High-Frequency Capacitive Discharges

Summary form only given. Several phenomena associated with nonlocal electron kinetics are found in high-frequency capacitive discharges through particle-in-cell/Monte Carlo simulations. From the spatial profile of the electron power deposition, the negative RF power deposition is analyzed for different excitation frequencies. The non-monotonic structure of RF electric field which comes from the abrupt phase reversal of RF electric field is found. From the separate calculations for low-and high-energy electron groups, the second layer in high-energy electron current is also observed