Changwon, South Korea
Changwon, South Korea

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Yun J.,Korea Institute of Materials Science
Advanced Functional Materials | Year: 2017

The need for the development of transparent conductive electrodes (TCEs) supported on flexible polymer substrates has explosively increased in response to flexible polymer-based photovoltaic and display technologies; these TCEs replace conventional indium tin oxide (ITO) that exhibits poor performance on heat-sensitive polymers. An efficient, flexible TCE is required to exhibit high electrical conductance and high optical transmittance, as well as excellent mechanical flexibility and long-term stability, simultaneously. Recent advances in technologies utilizing an ultrathin noble-metal film in a dielectric/metal/dielectric structure, or its derivatives, have attracted attention as promising alternatives that can satisfy the requirements of flexible TCEs. This review will survey the background knowledge and recent updates of synthetic strategies and design rules toward highly efficient, flexible TCEs based on ultrathin metal films, with a special focus on the principal features and available methodologies involved in the fabrication of highly transparent, conductive, ultrathin noble-metal films. This survey will also cover the practical applications of TCEs to flexible organic solar cells and light-emitting diodes. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Park S.S.,Ulsan National Institute of Science and Technology | You B.S.,Korea Institute of Materials Science
Scripta Materialia | Year: 2011

The tensile properties of extruded Mg-Sn-Al-Zn alloy at elevated temperature were investigated. Low-temperature superplasticity was found in the alloy, which exhibited tensile elongations of 410-950% at strain rates in the range 1 × 10-3-1 × 10-4 s-1 at 473 K. The superplastic deformation behavior was attributed to the fine-grained microstructure, which contained thermally stable Mg2Sn precipitates. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Sung J.H.,Ohio State University | Kim J.H.,Korea Institute of Materials Science | Wagoner R.H.,Ohio State University
International Journal of Plasticity | Year: 2010

An empirical plasticity constitutive form describing the flow stress as a function of strain, strain-rate, and temperature has been developed, fit to data for three dual-phase (DP) steels, and compared with independent experiments outside of the fit domain. Dubbed the "H/V model" (for "Hollomon/Voce"), the function consists of three multiplicative functions describing (a) strain hardening, (b) strain-rate sensitivity, and (c) temperature sensitivity. Neither the multiplicative structure nor the choice of functions (b) or (c) is novel. The strain hardening function, (a), has two novel features: (1) it incorporates a linear combination coefficient, α, that allows representation of Hollomon (power law) behavior (α = 1), Voce (saturation) behavior (α = 0) or any intermediate case (0 < α < 1, and (2) it allows incorporation of the temperature sensitivity of strain hardening rate in a natural way by allowing α to vary with temperature (in the simplest case, linearly). This form therefore allows a natural transition from unbounded strain hardening at low temperatures toward saturation behavior at higher temperatures, consistent with many observations. Hollomon, Voce, H/V models and others selected as representative from the literature were fit for DP590, DP780, and DP980 steels by least-squares using a series of tensile tests up to the uniform strain conducted over a range of temperatures. Jump-rate tests were used to probe strain rate sensitivity. The selected laws were then used with coupled thermo-mechanical finite element (FE) modeling to predict behavior for tests outside the fit range: non-isothermal tensile tests beyond the uniform strain at room temperatures, isothermal tensile tests beyond the uniform strain at several temperatures and hydraulic bulge tests at room temperature. The agreement was best for the H/V model, which captured strain hardening at high strain accurately as well as the variation of strain hardening with temperature. The agreement of FE predictions up to the tensile failure strain illustrates the critical role of deformation-induced heating in high-strength/high ductility alloys, the importance of having a constitutive model that is accurate at large strains, and the implication that damage and void growth are unlikely to be determinant factors in the tensile failure of these alloys. The new constitutive model may have application for a wide range of alloys beyond DP steels, and it may be extended to larger strain rate and temperature ranges using alternate forms of strain rate sensitivity and thermal softening appearing in the literature. © 2010 Elsevier Ltd. All rights reserved.

Lee Y.,Gwangju Institute of Science and Technology | Geckeler K.E.,Korea Institute of Materials Science
Advanced Materials | Year: 2010

With the increasing interest in the biological applications of carbon nanotubes, their interactions in the biological interphase and their general cytotoxicity have become major issues. In spite of their salient properties, major hurdles still exist for their use in biological applications, due to their main characteristics, including their hydrophobic surfaces and tendency to aggregate, as well as their unknown interactions in the cellular interphase. In this Research News, these characteristics of carbon nanotubes, a model nanomaterial, are investigated. Thus, the cytotoxicity of carbon nanotubes, the infl uence of functionalization, as well as their interactions with different mammalian cell lines are studied. Moreover, suggestions for the improvement of their biocompatibility and the design of biocompatible carbon nanotube-based systems are provided. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Han S.H.,Korea Institute of Materials Science | Lee J.-S.,Korea Institute of Materials Science
Langmuir | Year: 2012

We have developed a facile method to rapidly synthesize the monodisperse silver nanowire-DNA conjugates with a constant diameter and systematically controllable lengths in the range of 0.5-2.5 μm. The synthesis of silver nanowires takes advantage of poly(sodium 4-styrenesulfonate) as a structure-directing reagent and is performed under very mild conditions such as room temperature and aqueous media. The nanowires are densely conjugated with DNA sequences enough to exhibit the cooperative properties for the sensitive and selective detection of DNA targets. The limit of detection is 50 pM. © 2011 American Chemical Society.

The mechanical properties and microstructures of alternative low carbon TRIP-aided steels in which manganese contents mediate between conventional low-alloyed TRIP-aided steels and TWIP steel have been investigated. A variety of microstructures, from a single austenite phase to multiple phase mixtures, was attained according to chemical compositions as well as heat treatment schedule. By means of reverse transformation of martensite combined with controlled annealing, a remarkable grain refinement being responsible for stabilization of austenite could be achieved. In case of the duplex (α + γ) microstructures in 6Mn and 7Mn alloys, large amount of retained austenite more than 30 % contributed to substantial improvement of ductility compared to the conventional TRIP-aided steels having similar tensile strength level. In nearly single austenitic 13Mn alloy, the annealed sheet steel exhibited high tensile strength of 1.3 GPa with sufficient ductility due to the stain induced martensite transformation of fine grained austenite. © (2010) Trans Tech Publications.

Yun H.S.,Korea Institute of Materials Science
International journal of nanomedicine | Year: 2011

Mesoporous bioactive glasses (MBGs) are very attractive materials for use in bone tissue regeneration because of their extraordinarily high bone-forming bioactivity in vitro. That is, MBGs may induce the rapid formation of hydroxy apatite (HA) in simulated body fluid (SBF), which is a major inorganic component of bone extracellular matrix (ECM) and comes with both good osteoconductivity and high affinity to adsorb proteins. Meanwhile, the high bioactivity of MBGs may lead to an abrupt initial local pH variation during the initial Ca ion-leaching from MBGs at the initial transplant stage, which may induce unexpected negative effects on using them in in vivo application. In this study we suggest a new way of using MBGs in bone tissue regeneration that can improve the strength and make up for the weakness of MBGs. We applied the outstanding bone-forming bioactivity of MBG to coat the main ECM components HA and collagen on the MBG-polycarplolactone (PCL) composite scaffolds for improving their function as bone scaffolds in tissue regeneration. This precoating process can also expect to reduce initial local pH variation of MBGs. The MBG-PCL scaffolds were immersed in the mixed solution of the collagen and SBF at 37°C for 24 hours. The coating of ECM components on the MBG-PCL scaffolds and the effect of ECM coating on in vitro cell behaviors were confirmed. The ECM components were fully coated on MBG-PCL scaffolds after immersing in SBF containing dilute collagen-I solution only for 24 hours due to the high bone-forming bioactivity of MBG. Both cell affinity and osteoconductivity of MBG-PCL scaffolds were dramatically enhanced by this precoating process. The precoating process of ECM components on MBG-PCL scaffold using a high bioactivity of MBG was not only effective in enhancing the functionality of scaffolds but also effective in eliminating the unexpected side effect. The MBG-PCL scaffold-coated ECM components ideally satisfied the required conditions of scaffold in tissue engineering, including 3D well-interconnected pore structures with high porosity, good bioactivity, enhanced cell affinity, biocompatibility, osteoconductivity, and sufficient mechanical properties, and promise excellent potential application in the field of biomaterials.

We have investigated the hybridization properties of DNA-gold nanoparticle conjugates and have discovered that the hybridization properties are dramatically affected by controlling various synthetic and environmental conditions. We have further demonstrated that moderate DNA loading instead of high loading per nanoparticle significantly enhances the hybridization rates of DNA-gold nanoparticle conjugates, which allows one to precisely design their hybridization properties to distinguish a single-nucleotide polymorphism (SNP). A diagnostic application for the colorimetric detection of an SNP associated with a mutation in the breast cancer gene BRCA1 has been carefully designed and demonstrated.

Kim J.-Y.,Korea Institute of Materials Science | Lee J.-S.,Korea Institute of Materials Science
Chemistry of Materials | Year: 2010

We have synthesized DNA-silver nanoprism conjugates using the thiol-silver interaction and have assembled them into anisotropic structures with distinctive optical properties simply by controlling thermodynamic conditions. The reversible assembly formation takes advantage of the natural anisotropic architecture of the silver nanoprisms and the cooperative properties of their DNA conjugates. The anisotropic assemblies have been observed not only ex situ by TEM but also in situ in a solution by UV-vis spectroscopy. We have further investigated biodiagnostic applications of the DNA-silver nanoprism conjugates for the colorimetric and quantitative detection of DNA with high selectivity and sensitivity in the full visible range based upon their unique distant-dependent optical properties. © 2010 American Chemical Society.

Kang H.,Korea Institute of Materials Science | Hong S.,Korea Institute of Materials Science | Lee J.,Korea Institute of Materials Science | Lee K.,Korea Institute of Materials Science
Advanced Materials | Year: 2012

Nonconjugated polyelectrolytes (NPEs) are ideal interfacial layers for high-efficiency inverted polymer solar cells (I-PSCs). The NPEs are coated on indium tin oxide (ITO) using ionic self-assembly. Due to dipole formation between the cationic amine of the NPE and the anionic oxygen of ITO, the work function of ITO is dramatically reduced from 4.8 to 4.0 eV. Using the modified ITO, UV-independent I-PSCs with high efficiencies of 6.3% are demonstrated. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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