Papers by Author: Hyo Jin Oh

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Authors: J.H. Kim, Nam Hee Lee, Hyo Jin Oh, Cho Rong Yoon, Wheung Whoe Kim, Jae Sung Song, C.J. Jeon, Sun Jae Kim
Abstract: An electrophoretic solution using TiO2 nano particles is the most promising candidate in electronic paper industry because it offers various advantages such as ink-on-paper appearance, good contrast ratio, wide viewing angle, image stability in the off-state and extremely low power consumption. To prepare an electrophoretic solution of TiO2 nano particles with low apparent gravity for electronic paper, TiO2 powders were mixed with polyethylene powders using high energy planetary-mill in cyclohexane with low dielectric constant and transparency. The zeta-potential value of raw TiO2 particles in cyclohexane was measured about -80mV but that of polyethylene-coated TiO2 particles by milling was measured over -110mV, with showing good dispersibility by surfactant attached to them. Thus it was possible to control surface charge on the TiO2 particle by using optimum amount of surfactant after polyethylene coating on them for enhancement of dispersion stability.
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Authors: Yu Peng Guo, Nam Hee Lee, Hyo Jin Oh, Cho Rong Yoon, Chang Kyu Rhee, Kyung Sub Lee, Sun Jae Kim
Abstract: In this study, we have successfully developed the technology to grow the nanotube array thin films from dip-coated titania using hydrothermal method. The nanotube array thin film strongly adhered onto the substrate, was formed in short time reaction at 140°C. Even a self-supporting films, consisted of vertically aligned nanotube in large part, were formed after long time reactions at 140°C with 10 μm in thickness. The most probable formation mechanism of TiO2-based nanotube array thin films is discussed.
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Authors: Nam Hee Lee, J.H. Kim, Hyo Jin Oh, Sun Jae Kim
Abstract: To obtain a mass production of nanocrystalline ZnO powders, equipment that combines the conventional self-sustaining combustion process (SCP) with the ultrasonic spraying combustion method (USCM) were applied. The droplet was sprayed into the reaction zone of the furnace to carry out USCM that produces softly agglomerated crystalline ZnO particle with spherical shape. It was confirmed that the ZnO powder was prepared from ultrasonic spraying combustion method having smaller primary particle size, spherical shape with weak agglomeration and larger specific surface area than from conventional self-sustaining combustion method. Synthesized nanocrystalline ZnO powders have primary particle size in a range of 20∼30 nm, and specific surface area of about 20 m2/g under the optimum ultrasonic spray conditions.
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Authors: J.H. Kim, Hyo Jin Oh, Nam Hee Lee, S.H. Shin, Sun Jae Kim
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Authors: M. Qamar, Cho Rong Yoon, Hyo Jin Oh, Anna Czoska, K. Park, Nam Hee Lee, K.S. Lee, Sun Jae Kim
Abstract: The TiO2 sol was prepared hydrothermally in an autoclave from aqueous TiOCl2 solutions as starting precursor. Hollow fibers were obtained when sol-gel derived TiO2 sol was treated chemically with NaOH solution and subsequently heated in autoclave under various conditions. A systematic analysis of the influence of different NaOH concentrations on the formation of nanotubes has been carried out using XRD and SEM. The phase structure of the synthesized material was determined by transmission electron microscopy and found that these materials are, infact, hollow fibers widely known as nanotubes. From the TEM images, the outer and inner diameters of the tubes were measured ca. 8 and about 4 nm, respectively, with several hundred nanometers in length.
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