Showing papers by "Kyu Hwan Oh published in 2015"

Stable silicon-ionic liquid interface for next-generation lithium-ion batteries

Abstract: We are currently in the midst of a race to discover and develop new battery materials capable of providing high energy-density at low cost. By combining a high-performance Si electrode architecture with a room temperature ionic liquid electrolyte, here we demonstrate a highly energy-dense lithium-ion cell with an impressively long cycling life, maintaining over 75% capacity after 500 cycles. Such high performance is enabled by a stable half-cell coulombic efficiency of 99.97%, averaged over the first 200 cycles. Equally as significant, our detailed characterization elucidates the previously convoluted mechanisms of the solid-electrolyte interphase on Si electrodes. We provide a theoretical simulation to model the interface and microstructural-compositional analyses that confirm our theoretical predictions and allow us to visualize the precise location and constitution of various interfacial components. This work provides new science related to the interfacial stability of Si-based materials while granting positive exposure to ionic liquid electrochemistry.

Extreme wettability of nanostructured glass fabricated by non-lithographic, anisotropic etching.

Abstract: Functional glass surfaces with the properties of superhydrophobicity/or superhydrohydrophilicity, anti-condensation or low reflectance require nano- or micro-scale roughness, which is difficult to fabricate directly on glass surfaces. Here, we report a novel non-lithographic method for the fabrication of nanostructures on glass; this method introduces a sacrificial SiO2 layer for anisotropic plasma etching. The first step was to form nanopillars on SiO2 layer-coated glass by using preferential CF4 plasma etching. With continuous plasma etching, the SiO2 pillars become etch-resistant masks on the glass; thus, the glass regions covered by the SiO2 pillars are etched slowly, and the regions with no SiO2 pillars are etched rapidly, resulting in nanopatterned glass. The glass surface that is etched with CF4 plasma becomes superhydrophilic because of its high surface energy, as well as its nano-scale roughness and high aspect ratio. Upon applying a subsequent hydrophobic coating to the nanostructured glass, a superhydrophobic surface was achieved. The light transmission of the glass was relatively unaffected by the nanostructures, whereas the reflectance was significantly reduced by the increase in nanopattern roughness on the glass.

UV-responsive nano-sponge for oil absorption and desorption

Abstract: Controlled surface wettability for oil has been intensively studied to remove industrial oil waste or oil spill pollution from seas or rivers In particular, external stimuli-induced special wetting materials, such as photo-responsive TiO2, have attracted considerable attention for oil-water separation In this study, a novel method is reported to fabricate a nano-sponge which is composed of hydrophobic hydrocarbon and hydrophilic TiO2 nanoparticles for oil absorption or desorption that are responsive to UV irradiation The hydrocarbon in the nano-sponge could selectively absorb oil from water, whereas the absorbed oil is released into the water by TiO2 in response to UV irradiation The nano-sponge functionalized porous polydimethylsiloxane released more than 98% of the absorbed crude oil with UV irradiation and air-bubbling It could be continuously reused while maintaining a high absorption capacity and desorption efficiency without incurring secondary air or water pollution This smart oil absorption/desorption methodology with excellent selectivity and recyclability with almost perfect removal of absorbed oil can be applied for oil-water separation, oil spill cleanup and reuse of spilled oil

Plasma-Induced Hetero-Nanostructures on a Polymer with Selective Metal Co-Deposition

Abstract: Plasma-induced pattern formation is explored on polyethylene terephthalate (PET) using an oxygen plasma glow discharge. The nanostructures on PET are formed through preferential etching directed by the co-deposition of metallic elements, such as Cr or Fe, sputtered from a stainless-steel cathode. The local islands formed by metal co-deposition have significantly slower etching rates than those of the pristine regions on PET, generating anisotropic nanostructures in pillar- or hair-like form during plasma etching. By covering the cathode with the appropriate material, the desired metallic or polymeric elements can be co-deposited onto the target surfaces. When the cathode is covered by a relatively soft material composed of only carbon and hydrogen, such as polystyrene, nanostructures typically induced by preferential etching are not observed on the PET surface, and the surfaces are uniformly etched. A variety of metals, such as Ag, Cu, Pt, or Si, can be successfully co-deposited onto the PET surfaces by simply using a cathode covered in the desired metal; high-aspect-ratio nanostructures coated with the co-deposited metal are subsequently formed. Therefore this simple single-step method for forming hetero-nanostructures—that is, nanoscale hair-like polymer structures decorated with metals—can be used to produce nanostructures for various applications, such as catalysts, sensors, or energy devices.

Dehydrogenation Reaction Pathway of the LiBH4–MgH2 Composite under Various Pressure Conditions

Abstract: This paper investigates dehydrogenation reaction behavior of the LiBH4–MgH2 composite at 450 °C under various hydrogen and argon back-pressure conditions. While the individual decompositions of LiBH4 and MgH2 simultaneously occur under 0.1 MPa H2, the dehydrogenation of MgH2 into Mg first takes place and subsequent reaction between LiBH4 and Mg into LiH and MgB2 after an incubation period under 0.5 MPa H2. Under 1 MPa H2, enhanced dehydrogenation kinetics for the same reaction pathway as that under 0.5 MPa H2 is obtained without the incubation period. However, the dehydrogenation reaction is significantly suppressed under 2 MPa H2. The formation of Li2B12H12 as an intermediate product during dehydrogenation seems to be responsible for the incubation period. The degradation in hydrogen capacity during hydrogen sorption cycles is not prevented with the dehydrogenation under 1 MPa H2, which effectively suppresses the formation of Li2B12H12. The overall dehydrogenation behavior under argon pressure conditions...

Tin Networked Electrode Providing Enhanced Volumetric Capacity and Pressureless Operation for All-Solid-State Li-Ion Batteries

Abstract: Pure tin (Sn) metal nano-powder is investigated as a high capacity negative electrode for rechargeable all-solid-state Li-ion batteries. Sn is used to form a fully dense network intertwining with solid electrolyte negating necessary conductive additive. Galvanostatic cycling of the Sn composite electrode delivers a reversible capacity 800 mAh g −1 of Sn with a constant coulombic efficiency over 99.2%.Wereportontheeffectofpressureandrateuponthedelithiationmechanics,drawingcorrelationsbetweenSnvolumeincrease factors and stress accumulation over the course of Sn-Li phase transformations. Due to the fabricated electrode microstructure, we are able to operate the cell at ambient pressure conditions ‐ the next step toward commercialization of the solid-state battery. We believe that this initial work provides new opportunities to study the electrochemical expansion of Sn with the inclusion of rigid electrolyte particles. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any

Protective role of quercetin against cisplatin-induced hair cell damage in zebrafish embryos.

Abstract: Background and objectives:The aim of this study was to evaluate the protective effects of quercetin on cisplatin-induced hair cell damage in transgenic zebrafish embryos.Materials and methods:Five days postfertilization zebrafish embryos were exposed to 1 mM cisplatin and quercetin at 10, 50, 100, or 200 μM for 4 h. Hair cells within neuromasts of the supraorbital, otic, and occipital lateral lines were analyzed by fluorescent microscopy (n = 10). Survival of hair cells was calculated as the average number of hair cells in the control group that were not exposed to cisplatin. Ultrastructural changes were evaluated using scanning electron microscopy.Results:Hair cell damage in neuromasts was decreased by co-treatment of quercetin and cisplatin (quercetin 100 μM: 8.6 ± 1.1 cells; 1 mM cisplatin only: 5.0 ± 0.5 cells; n = 10, p < 0.05); apoptosis of hair cells examined by special stain was also decreased by quercetin. The ultrastructure of hair cells within neuromasts was preserved in zebrafish by the combin...

High performance gas diffusion layer with hydrophobic nanolayer under a supersaturated operation condition for fuel cells.

Abstract: Reliable operation of a proton exchange membrane fuel cell requires proper water management to prevent water flooding in porous carbon materials such as the gas diffusion layer (GDL). In contrast to the conventional GDL that uses the “wet” dip-coating process with solvent and expensive polytetrafluoroethylene, we have proposed a novel GDL with a controlled hydrophobic silicone (i.e., hexamethyldisiloxane) nanolayer by a highly efficient and cost-effective “dry” deposition process. The GDL with the nanolayer exhibited an increased contact angle, decreased contact angle hysteresis, and suppressed water condensation. Even though the GDL with the nanolayer had a higher electrical resistance than the pristine GDL, the cell performance of the GDL with an optimum nanolayer thickness of 8.6 nm was practically the same as that of the pristine GDL under normal operating conditions. Under a supersaturated condition, the GDL with optimum nanolayer thickness exhibited much higher cell performance than the pristine GDL...

Gelation dynamics of ionically crosslinked alginate gel with various cations

Abstract: Alginates can be crosslinked with multivalent cations, leading eventually to hydrogel formation. The properties of alginate gel depend on its lock structure, monomeric composition, concentration of polymer and cross linker. Among these, the properties of ionically crosslinked alginate gel can be greatly affected by multivalent cations as cross-linker. Knowledge of gelation dynamics by multivalent cations allows control over gelation characteristics, such as modulus of gel and the time required for equilibrium state, and healing properties. We have studied gelation dynamics of ionically crosslinked alginate gel. According to different types of anions bound with cations, gelation time and equilibrium viscosity was changed due to the solubility kinetics of the cation. The equilibrium viscosity is increased as the size of the cations increased even though the cations have same valency. A theoretical model is introduced to interpret dynamic change of viscosity during gelation. Open image in new window

Biofunctionalized ceramic with self-assembled networks of nanochannels.

Abstract: Nature designs circulatory systems with hierarchically organized networks of gradually tapered channels ranging from micrometer to nanometer in diameter. In most hard tissues in biological systems, fluid, gases, nutrients and wastes are constantly exchanged through such networks. Here, we developed a biologically inspired, hierarchically organized structure in ceramic to achieve effective permeation with minimum void region, using fabrication methods that create a long-range, highly interconnected nanochannel system in a ceramic biomaterial. This design of a synthetic model-material was implemented through a novel pressurized sintering process formulated to induce a gradual tapering in channel diameter based on pressure-dependent polymer agglomeration. The resulting system allows long-range, efficient transport of fluid and nutrients into sites and interfaces that conventional fluid conduction cannot reach without external force. We demonstrate the ability of mammalian bone-forming cells placed at the dis...

The effect of energetically coated ZrOx on enhanced electrochemical performances of Li(Ni1/3Co1/3Mn1/3)O2 cathodes using modified radio frequency (RF) sputtering

Abstract: To date, most coating layers for electrode materials for Li-ion batteries have been fabricated using the sol–gel method or atomic layer deposition (ALD), which involve complicated processing steps and limited candidates for coating materials. With an emphasis on solving these issues, herein, a new coating methodology based on a sputtering system was developed, and sputtered zirconium oxide was coated on Li(Ni1/3Co1/3Mn1/3)O2 (L333) cathode powders. The continuous movement of the cathode powders during the coating procedure and the high kinetic energy from the sputtering process resulted in a highly uniform coating layer with multiple structures exhibiting a concentration and valence state gradient of Zr, i.e., surface (mainly Zr4+) and doped (mainly Zr2+) layers. The ZrOx-coated L333 powders exhibited an outstanding capacity retention (96.3% at the 200th cycle) and superior rate capability compared with the uncoated version in a coin cell with 1 M LiPF6 in EC:DEC liquid electrolyte. The ZrOx-coated L333 powders also exhibited an enhanced specific capacity in a solid state battery cell with a sulfide-based inorganic solid-state electrolyte. The improved electrochemical performance of ZrOx/L333 was attributed to the synergetic effect from the surface and doped layers: physical/chemical protection of the active material surface, enhancement of Li-ion diffusion kinetics, and stabilization of the interfaces.

Nano composite structure with nano patterned structure on its surface and method of preparing the same

Abstract: Provided are a method of producing a nano composite structure and a nano composite structure produced by using the same. The method comprises producing a substrate; placing a metal net structure above the substrate; and plasma treating the substrate above which the metal net structure is placed. The method allows a nano composite structure with a nano patterned structure on its overall surface to be easily produced. The nano composite structure includes a substrate having a plurality of first protrusions constituting a nano pattern on its surface; and an inorganic particle disposed on an end of at least a portion of the first protrusions.

Columnar grown copper films on polyimides strained beyond 100

Abstract: Many flexible electronic devices contain metal films on polymer substrates to satisfy requirements for both electrical conductivity and mechanical durability. Despite numerous trials to date, the stretchability of metal interconnects remains an issue. In this paper, we have demonstrated a stretchable metal interconnect through control of the texture of a copper film with columnar grown grains on a polyimide (PI) substrate. The columnar grown copper films (CGC films) were deposited by regulating radio frequency (RF) sputtering powers. CGC films were able to sustain their electrical conductivity at strains above 100%. Instead of ultimate electrical discontinuity by channel crack propagation, CGC films maintained their conductivity by forming ligament structures, or a ‘conductive net,’ through trapped micro-cracks. XRD, AFM and in situ SEM analysis were used to investigate these stretchable conductors.

Super-hydrophobic fiber having needle-shaped nano structure on its surface, method for fabricating the same and fiber product comprising the same

Abstract: A super-hydrophobic fiber of the present disclosure includes: a nano-needle fiber having a surface including needle-shaped nano structures; and a coating layer disposed on the surface including the nano structures, and containing a hydrophobic material. The fiber has no aging effect, and thus, is excellent in durability, and has such a large contact angle and such as small sliding angle that the fiber may not be wet with water. A method for fabricating the super-hydrophobic fiber includes: a preparation step of preparing a pre-treating fiber; an etching step of etching a surface and an inner portion of the pre-treating fiber to fabricate a nano-needle fiber having a surface on which needle-shaped nano structures are formed; and a coating step of forming a coating layer containing a hydrophobic material, and enables mass production and is performed by simple processes. Further, an article including the super-hydrophobic fiber is an article in which no liquid drop is absorbed, scarcely adsorbs a contaminant, needs not be dried, and thus, may be widely applied even to recreational articles.

A Shear Strain Route Dependency of Martensite Formation in 316L Stainless Steel.

Abstract: In this study, the effect of simple shearing on microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. Two different shear strain routes were obtained by twisting cylindrical specimens in the forward and backward directions. The strain-induced martensite phase was effectively obtained by alteration of the routes. Formation of the martensite phase clearly resulted in significant hardening of the steel. Grain-size reduction and strain-induced martensitic transformation within the deformed structures of the strained specimens were characterized by scanning electron microscopy - electron back-scattered diffraction, X-ray diffraction, and the TEM-ASTAR (transmission electron microscopy - analytical scanning transmission atomic resolution, automatic crystal orientation/phase mapping for TEM) system. Significant numbers of twin networks were formed by alteration of the shear strain routes, and the martensite phases were nucleated at the twin interfaces.

Observation of Micro-scale Surface Morphology with Microtexture Development During Plane Strain Tensile Deformation in AZ31 Magnesium Alloy

Abstract: The change of microstructure including microtexture and surface morphology in AZ31 magnesium alloy under plane strain tension was investigated by 3D observation combined confocal microscope and high-resolution electron backscattered diffraction. Micro-scale changes in the surface morphology were observed on the area including $$ \left\{ { 10\overline{1} 2} \right\} $$ $$ \langle 10\overline{1} 1\rangle $$ tensile twin bands. The mechanism for surface morphology variation was discussed with the nucleation of tensile twinning and the strain partitioning caused by continuing deformation after the nucleation of the twins.

Stress and Displacement Analysis of Arctic Frostheave with Gas Pipeline using Finite Element Method

Abstract: According to the interest of the arctic's resources rising, many countries are making moves to develop these resources. Korea has also undergone negotiations with Russia to develop natural gas resources in Siberia, which is geographically relatively close. However, the Arctic resources market is dominate, it is essential to develop construction techniques that are suited for the Arctic. Gas pipelines in the Arctic are affected by frost heave due to the region's extremely low temperatures, a condition that is not present in Korea, making it vital to develop a finite element method (FEM) model. This research paper study a model of gas pipe lines in the Arctic and frost heave using FEM.

***WITHDRAWN PATENT AS PER THE LATEST USPTO WITHDRAWN LIST***Method of preparing micro/nano hybrid woven fabric surfaces for oil-oil filtration or oil-water filtration

Abstract: A method to prepare polymer woven fabric surface with selective oleophilicity or hydrophobicity and oil-oil separation and oil-water separation filter prepared by using the surface. The method to prepare the surface with selective oleophilicity or hydrophobicity includes steps comprising a step to form nano meter sized pores on the surface of the polymer woven fabric surface with micro sized pores through drying type etching; and a step to form selective oleophobic or hydrophobic film on the nano meter sized pores. It is possible to control hydrophobic/oleophobic property according to pore size, material or thickness of the film and this polymer surface with hybrid pores can be used in various areas such as an oil filter for car capable of selective separation of oil-oil mixture and water-oil mixture, disposal of waste oil, treatment of marine oil leakage, and pretreatment of crude oil refinement.