• Corrosion Science and Technology
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• v.15 no.2
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• pp.92-107
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• 2016

Graphene was coated on austenitic and martensitic stainless steels to simulate the metallic bipolar plate of proton exchange membrane fuel cell (PEMFC). Graphene oxide (GO) was synthesized and was reduced to reduced graphene oxide (rGO) via a hydrazine process. rGO was confirmed by FE-SEM, Raman spectroscopy and XPS. Interfacial contact resistance (ICR) between the bipolar plate and the gas diffusion layer (GDL) was measured to confirm the electrical conductivity. Both ICR and corrosion current density decreased on graphene coated stainless steels. Corrosion resistance was also improved with immersion time in cathodic environments and satisfied the criteria of the Department of Energy (DOE), USA. The total concentrations of metal ions dissolved from graphene coated stainless steels were reduced. Furthermore hydrophobicity was improved by increasing the contact angle.

• Polymer Science and Technology
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• v.6 no.4
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• pp.348-357
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• 1995

• Bulletin of the Korean Chemical Society
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• v.34 no.11
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• pp.3269-3273
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• 2013

Graphene oxide (GO) has been of particular interest because it provides unique properties due to its high surface area, chemical functionality and ease of mass production. GO is produced by chemical exfoliation of graphite and is decorated with oxygen-containing groups such as phenol hydroxyl, epoxide groups and ionizable carboxylic acid groups. Due to the presence of those functional groups, GO can be utilized as a novel platform for hybrid nanocomposites in chemical synthetic approaches. In this work, GO-$SnO_2$ nanocomposites have been prepared through the spontaneous formation of molecular hybrids. When $SnO_2$ precursor solution and GO suspension were simply mixed, $Sn^{2+}$ was spontaneously formed into $SnO_2$ nanoparticles upon the deoxygenation of GO. Through further chemical reduction by adding hydrazine, reduced GO-$SnO_2$ hybrid was finally created. Our investigation for the electrocapacitive properties of hybrid electrode showed the enhanced performance (389 F/g), compared with rGO-only electrode (241 F/g). Our approach offers a scalable, robust synthetic route to prepare graphene-based nanocomposites for supercapacitor electrode via spontaneous hybridization.

• Journal of Powder Materials
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• v.26 no.3
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• pp.220-224
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• 2019

The aluminum (Al)/copper oxide (CuO) complex is known as the most promising material for thermite reactions, releasing a high heat and pressure through ignition or thermal heating. To improve the reaction rate and wettability for handling safety, nanosized primary particles are applied on Al/CuO composite for energetic materials in explosives or propellants. Herein, graphene oxide (GO) is adopted for the Al/CuO composites as the functional supporting materials, preventing a phase-separation between solvent and composites, leading to a significantly enhanced reactivity. The characterizations of Al/CuO decorated on GO(Al/CuO/GO) are performed through scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy mapping analysis. Moreover, the functional bridging between Al/CuO and GO is suggested by identifying the chemical bonding with GO in X-ray photoelectron spectroscopy analysis. The reactivity of Al/CuO/GO composites is evaluated by comparing the maximum pressure and rate of the pressure increase of Al/CuO and Al/CuO/GO. The composites with a specific concentration of GO (10 wt%) demonstrate a well-dispersed mixture in hexane solution without phase separation.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.201-201
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• 2013

ITO는 투명하면서도 전도성이 매우 높은 물질로 디스플레이 분야에서 전극으로 많이 사용된다. 하지만 ITO는 세라믹 물질이기 때문에 공정 단가가 높고, 유연성이 낮아 구부릴 경우 전도성이 파괴되며 충격에도 약하여 flexible한 소자에 적용할 수 없다. 또한 metal diffusion이 잘 일어나는 물질이기 때문에 OLED 소자의 특성을 저해한다. 이와 같은 문제점을 해결하기 위해 ITO를 대체하여 graphene을 이용한 투명전극 연구개발이 활발히 진행되고 있다. Graphene은 높은 mobility와 전도도를 가지고 있으며, 높은 열전도성, Young's modulus, 그리고 mechanical flexibility를 가진 물질이다. 최근에 이러한 장점들로 인해 ITO를 대체하는 물질로서 각광을 받고 있지만 graphene은 Cu, Ni과 같은 금속표면에 한정되어 성장하는 문제점을 가지고 있다. 이 graphene 합성방법은 전사과정을 필요로 하며, 이로 인해 낮은 생산성과 낮은 수율을 야기한다. 최근 높은 생산성을 가지는 graphene 전극을 만들기 위해 Reduced Graphene Oxide (rGO) 연구가 활발히 진행되고 있다. 그러나 rGO는 산화환원 과정에서 전기전도도와 electron mobility가 완벽히 회복되지 못한다는 문제점을 가지고 있다. 그리하여 본 연구에서는 높은 투과도와 높은 전도도를 갖는 graphene 전극을 얻기 위해서 powdered graphene flake를 사용하였다. Graphene flake를 IPA solvent에 분산시키기 위해 sonicator과 homogenizer를 이용하여 Graphene flake solution을 제작하였다. 그리고 uniform한 전극을 만들기 위해 Spray Coating 방법을 이용하여 PET 기판 위에 graphene flake를 증착시켰다. graphene flake를 이용하여 높은 투과도와 낮은 면저항을 갖는 투명전극을 제작하고, 그 특성을 UV-visible spectrophotometer과 four point probe를 이용하여 확인하였다.

• Carbon letters
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• v.27
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• pp.26-34
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• 2018

To formulate folate receptor (FR)-specific graphene-based electrochemical electrodes, a folic acid (FA) derivative attached with two pyrene molecules on the glutamate tail of FA was synthesized. The resulting pyrene-functionalized FA (FA-Py) presented the spontaneous noncovalent binding on chemically reduced graphene oxides (rGO) through an ${\pi}-{\pi}$ interaction. Ultrathin morphology, high water-resistance, and preservation of intact FR-specific pteroates from the rGO/FA-Py assembly allow this assembly to be exploited as robust and FR-specific electrochemical electrode materials. The limits of detecting rGO/FA-Py modified electrodes were found to be as low as 3.07 nM in FR concentrations in cyclic voltammetry analysis.

• Journal of the Chungcheong Mathematical Society
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• v.32 no.4
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• pp.401-408
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• 2019

A ring R is called right (resp., left) nilpotent-duo if N(R)a ⊆ aN(R) (resp., aN(R) ⊆ N(R)a) for every a ∈ R, where N(R) is the set of all nilpotents in R. In this article we provide other proofs of known results and other computations for known examples in relation with right nilpotent-duo property. Furthermore we show that the left nilpotent-duo property does not go up to a kind of matrix ring.

• Nutrition Research and Practice
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• v.14 no.4
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• pp.412-422
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• 2020

BACKGROUND/OBJECTIVES: This study investigates correlations between circulating microRNAs (miRNAs) and obesity-related parameters among young women (aged 20-30 years old) in Korea. SUBJECTS/METHODS: We analyzed TaqMan low density arrays (TLDAs) of circulating miRNAs in 9 lean (body mass index [BMI] < 25 kg/㎡) and 15 obese (BMI > 25 kg/㎡) women. We also performed gene ontology (GO) analyses of the biological functions of predicted miRNA target genes, and clustered the results using the database for annotation, visualization and integrated discovery. RESULTS: The TLDA cards contain 754 human miRNAs; of these, the levels of 8 circulating miRNAs significantly declined (> 2-fold) in obese subjects compared with those in lean subjects, including miR-1227, miR-144-5p, miR-192, miR-320, miR-320b, miR-484, miR-324-3p, and miR-378. Among them, miR-484 and miR-378 displayed the most significant inverse correlations with BMI (miR-484, r = -0.5484, P = 0.0056; miR-378, r = -0.5538, P = 0.0050) and visceral fat content (miR-484, r = -0.6141, P = 0.0014; miR-378, r = -0.6090, P = 0.0017). GO analysis indicated that genes targeted by miR-484 and miR-378 had major roles in carbohydrate and lipid metabolism. CONCLUSION: Our result showed the differentially expressed circulating miRNAs in obese subjects compared to lean subjects. Although the mechanistic study to reveal the causal role of miRNAs remains, these miRNAs may be novel biomarkers for obesity.

• Journal of Adhesion and Interface
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• v.13 no.3
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• pp.137-144
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• 2012

Chemical functionalization of carbon nanomaterials (CNMs) is generally carried out for increasing interfacial adhesion between filler and polymer matrix for CNM-polymer nanocomposites. The chemically functionalized CNTs can produce strong interfacial bonds with many polymers, allowing CNT based nanocomposites to possess high mechanical and functional properties. Hence, increased surface adhesion can be measured indirectly by observing increased mechanical properties. However, there is a more direct way to observe interfacial bonds between polymer and CNM by measuring piezoresistivity behavior so that we can imagine the behavior of CNM particles in polymer matrix under deflection. Fuctionalization of MWCNT and rGO was carried out by oxidization reaction of MWCNT and rGO with $H_2SO_4/HNO_3$ solution. Electrical resistivities of MWCNT-PMMA and rGO-PMMA composites were decreased after functionalization because of the destructive fuctionalization process. Meanwhile, piezoresistivities of functionalized CNM-PMMA composites showed more sensitive behavior under the same deflection as compared to pristine CNM-PMMA composites. Therefore, mobility of CNM in polymer matrix was found to be improved with chemical functionalization.

• IE interfaces
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• v.25 no.3
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• pp.309-318
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• 2012

Forecasting probability or likelihood of technology development success has been a crucial factor for critical decisions in technology management such as R&D project selection and go or no-go decision of new product development (NPD) projects. This paper proposes an analytic network process (ANP) approach to forecasting of technology development success. Reviewing literature on factors affecting technology development success has constructed the ANP model composed of four criteria clusters : R&D characteristics, R&D competency, technological characteristics, and technological environment. An alternative cluster comprised of two elements, success and failure is also included in the model. The working of the proposed approach is provided with the help of a case study example of MRAM (magnetic random access memory) technology.