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Park J.H.,Korea Institute of Science and TechnologySeoul | Lee S.W.,Seoul National UniversitySeoul | Song D.S.,Seoul National UniversitySeoul | Jho J.Y.,Seoul National UniversitySeoul
ACS Applied Materials and Interfaces | Year: 2015

On purpose to enhance the generating force of ionic polymer-metal composite (IPMC) actuators, the thickness of the ion-exchange membrane is manipulated in two different ways. One is grafting poly(styrenesulfonic acid) onto poly(vinylidene fluoride-co-hexafluoropropylene) films with varying thickness, and the other is stacking pre-extruded Nafion films to thicker films by pressing at high temperatures. For both groups of the membranes, ionic properties including ion-exchange capacity and ionic conductivity are maintained similarly inside the groups regardless of the thickness. The actuation tests clearly show the increase in generating force with increasing thickness of the IPMCs prepared. It is due to a larger bending stiffness of thicker IPMCs, which is consistent with the predicted result from the cantilever beam model. The increase in force is more remarkable in Nafion-stacked IPMCs, and a thick IPMC lifts a weight of 100 g, which far exceeds the reported values for IPMCs. © 2015 American Chemical Society. Source

Park J.,Chung - Ang University | Park J.,Korea Institute of Science and TechnologySeoul | Kim S.,Chung - Ang University | Sim Y.,Chung - Ang University | And 7 more authors.
Journal of Alloys and Compounds | Year: 2016

CdS nanowires were synthesized using a simple synthesis process using Au nanoparticles (average diameter: 13 nm) as catalyst. The growth conditions were optimized by varying the substrate temperature and the growth time of a thermal chemical-vapor-deposition system. CdS nanowires were successfully grown at temperatures above 480 °C. In fact, high-quality nanowires, with hexagonal wurtzite structures and an average diameter of 25 nm and length of 1.46 μm, were obtained after a 30-min synthesis at a growth temperature of 520 °C. Electron microscope images revealed that our CdS nanowires, grown at relatively lower growth temperatures, have higher average-aspect-ratio and smaller average-diameter than those previously reported in the literature. Our synthesis method resulted in CdS nanowires only without producing nanorods and nanobelts, which make it unnecessary to filter and purify nanowires from the mixture of nanowires, nanorods, and nanobelts. © 2015 Elsevier B.V. Source

Oh Y.,Wilmer Eye Institute | Park O.,Wilmer Eye Institute | Swierczewska M.,Wilmer Eye Institute | Park J.-S.,Wilmer Eye Institute | And 9 more authors.
Hepatology | Year: 2016

Liver fibrosis is a common outcome of chronic liver disease that leads to liver cirrhosis and hepatocellular carcinoma. No US Food and Drug Administration-approved targeted antifibrotic therapy exists. Activated hepatic stellate cells (aHSCs) are the major cell types responsible for liver fibrosis; therefore, eradication of aHSCs, while preserving quiescent HSCs and other normal cells, is a logical strategy to stop and/or reverse liver fibrogenesis/fibrosis. However, there are no effective approaches to specifically deplete aHSCs during fibrosis without systemic toxicity. aHSCs are associated with elevated expression of death receptors and become sensitive to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced cell death. Treatment with recombinant TRAIL could be a potential strategy to ameliorate liver fibrosis; however, the therapeutic application of recombinant TRAIL is halted due to its very short half-life. To overcome this problem, we previously generated PEGylated TRAIL (TRAILPEG) that has a much longer half-life in rodents than native-type TRAIL. In this study, we demonstrate that intravenous TRAILPEG has a markedly extended half-life over native-type TRAIL in nonhuman primates and has no toxicity in primary human hepatocytes. Intravenous injection of TRAILPEG directly induces apoptosis of aHSCs in vivo and ameliorates carbon tetrachloride-induced fibrosis/cirrhosis in rats by simultaneously down-regulating multiple key fibrotic markers that are associated with aHSCs. Conclusion: TRAIL-based therapies could serve as new therapeutics for liver fibrosis/cirrhosis and possibly other fibrotic diseases. © 2015 by the American Association for the Study of Liver Diseases. Source

Yoon S.,Chung - Ang University | Cho J.,Chung - Ang University | Lee H.-K.,Pohang Accelerator Laboratory | Park S.,Korea Institute of Science and TechnologySeoul | And 2 more authors.
Applied Physics Letters | Year: 2015

The effects of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) doping on diketopyrrolo-pyrrole-based polymeric semiconductors in terms of charge transport behavior and structural ordering are systematically investigated. Although the energy level offset between the polymeric semiconductor and the F4TCNQ acceptor was not particularly large, ultraviolet photoelectron spectroscopy analyses revealed that a low doping ratio of 1 wt. % is sufficient to tune the energy distance between the Fermi level and the HOMO level, reaching saturation at roughly 5 wt. %, which is further confirmed by the depletion mode measurements of field effect transistors (FETs). Structural analyses using grazing-incidence X-ray diffraction (GIXD) show that the overall degree of edge-on orientation is disturbed by the addition of dopants, with significant influence appearing at high doping ratios (>3 wt. %). The calculated charge carrier mobility from accumulation mode measurements of FETs showed a maximum value of 2 cm2/V·s at the optimized doping ratio of 1%, enabled by additional holes in the channel region, which results in a roughly 40% increase relative to the undoped device. Further increases in the doping ratio, however, resulted in worse FET performance, which can be attributed to structural deformation. This result suggests that the electrochemical doping method can be also applied to donor-acceptor copolymers to further enhance their charge transport characteristics, once the optimized doping condition has been established. © 2015 AIP Publishing LLC. Source

Ahn M.,Korea Institute of Science and Technology | Cha I.Y.,Korea Institute of Science and TechnologySeoul | Lee J.K.,Korea Institute of Science and Technology | Yoo S.J.,Korea Institute of Science and TechnologySeoul | And 2 more authors.
Journal of Materials Chemistry A | Year: 2015

Facile synthesis of Rh-Sn catalysts for the electrocatalytic oxidation of ethanol is carried out via a surfactant-free microwave-assisted method. The bifunctional mechanism and electronic modification with C-C bond splitting enable this electrocatalyst to be remarkably active and durable at high fuel concentrations, which allows for a significant reduction in the volume and weight of the fuel cell system. This journal is © The Royal Society of Chemistry. Source

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