• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.187.2-187.2
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• 2014

최근 다양한 카본 나노소재들이 열 전도성 필러로써 고분자 복합체의 열전도도 향상을 위해 연구되고 있다. 그러나 구조적 이방성을 갖는 탄소나노튜브(CNT) 혹은 그래핀나노플레이트(Graphene Nanoplatelet)를 복합체에 적용할 경우, 복합체의 수직 방향과 수평 방향에서의 열전도도가 3배 이상 차이가 나는 문제가 있다. 따라서 본 연구에서는 2차원의 GNP 표면 위에 1차원의 CNT를 직접 성장시킨 하이브리드 탄소소재를 이용하여 이러한 열전도도 이방성을 개선하고자 하였다. 하이브리드 탄소소재는 무전해 도금법과 열기상법으로 제조하였다. 합성된 하이브리드 탄소소재 및 CNT를 단독 혹은 혼합하여 필러를 만들고 이를 에폭시 기지 내에 분산시켜 복합체를 제작하였다. 필러 함량별, 필러 비율별로 제작된 복합체의 열전도도를 레이저 플래시 법으로 측정 비교하였다. 결과적으로 기존의 단일 필러들보다 열전도도 이방성이 1.5배 이상 개선된 방열용 에폭시 복합체를 제작할 수 있었다. 한편 하이브리드 탄소와 2% 이하의 CNT 배합에서 단독 필러 투입에 비해 45% 이상의 열전도율 향상을 확인하였다. 이는 미세구조 분석 및 성분 분석 결과, 필러 분산 정도가 열전도도 향상의 주요 인자로 작용하는 것을 확인하였고 기지 내 CNT가 열전도도 경로로 작용하기보다는 하이브리드 탄소소재의 균일한 분산에 영향을 준 것으로 사료된다.

• Polymer(Korea)
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• v.39 no.3
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• pp.468-474
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• 2015

Electrically conductive polymer nanocomposites were prepared by the inclusion of graphene-based nanofillers. Graphene oxide (GO) and reduced graphene oxide wrapped by poly(styrene sulfonate) (PSS-RGO) were used as nanofillers to make good dispersion with the aqueous dispersion of polystyrene (PS) particles. GO sheets were synthesized by the modified Hummers' method from graphite, and PSS-RGO sheets were prepared by the reduction of GO-dispersed PSS solution with hydrazine monohydrate. Morphology and properties of PS/GO and PS/PSS-RGO nanocomposites via latex technology were investigated. Both nanofillers showed well dispersed morphology in PS matrix. Rheological and electrical percolation thresholds were 0.28 and 0.51 wt% for GO, and 0.50 and 1.01 wt% for PSS-RGO respectively. It is speculated that PS/GO nanocomposites showed better conductivity than PS/PSS-RGO counterparts due to the partial recovery of GO by thermal reduction during molding.

• Polymer(Korea)
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• v.38 no.2
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• pp.232-239
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• 2014

Poly(lactic acid)(PLA) nanocomposites containing various nanofillers were synthesized using the solution intercalation method. Organically modified bentonite clay (NSE), octadecylamine-graphene oxide (ODA-GO), and an NSE/ODA-GO complex were utilized as nanofillers in the fabrication of PLA hybrid films. PLA hybrid films with varying nanofiller contents in the range of 0-10 wt% were examined and compared in terms of their thermomechanical properties, morphologies, and oxygen permeabilities. Transmission electron microscopy (TEM) confirmed that most of the NSE and ODA-GO nanofillers were dispersed homogeneously throughout the PLA matrix on the nanoscale, although some agglomerate NSE/ODA-GO complex particles were also formed. Among the three nanofillers for PLA hybrid films, the NSE/ODA-GO complex showed the best improvement in film thermal stability. In contrast, NSE and ODA-GO exhibited the best improvement in tensile mechanical properties and oxygen barrier properties of the PLA hybrid films, respectively.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1185-1186
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• 2015

본 논문에서 HVDC $SF_6$ 가스절연시스템(GIS)에서 최적의 에폭시 재질을 알아내기 위해 $Al_2O_3$와 $SiO_2$ 나노필러가 첨가된 총 다섯 종류의 에폭시에 대한 도전율을 측정하여 DC 전계분포 해석을 수행하였다. 해석결과 $75^{\circ}$의 접촉각(에폭시 스페이서와 도체가 이루는 각도)가 가장 우수한 전계특성을 나타냈고 $Al_2O_3$ 2 hundred per resin(phr)의 나노필러가 첨가된 에폭시가 가장 우수한 절연매질로써의 특성을 보여주었다. 또한, 삼중점에서 전계집중 완화를 위하여 $Al_2O_3$ 2 phr의 나노필러가 첨가된 에폭시의 데이터를 기반으로 열해석을 고려한 정상상태 및 극성 반전에 대해 DC 전계 해석을 수행하여 최적의 에폭시 스페이서 형상을 도출하였다.

• Polymer(Korea)
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• v.37 no.4
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• pp.494-499
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• 2013

Modified polypropylene (m-PP) was fabricated by furfuryl sulphide (FS) as branching agent and m-PP/nano-filler composites were prepared with silicate and multi-walled carbon nanotube (MWCNT), using a twin screw extruder. The chemical structures and thermal properties of the m-PP were investigated by FTIR and DSC. The chemical structure of the m-PP was confirmed by the existence of =C-H stretching peak of the branching agent at 3100 $cm^{-1}$. There was no district change in melting temperature in case of m-PP, but a certain increase in crystallization temperature was notified and the increase was in the range of $10-20^{\circ}C$. The rheological properties, filler dispersion and foaming behaviors of the m-PP/nano-filler composites were investigated by dynamic rheometer, X-ray diffractometer (XRD) and scanning/transmission electron microscope (SEM/TEM). m-PP/nano-filler composites showed a high complex viscosity at a low frequency, an increase in melt elasticity, and a high shear thinning effect. Compared to pure PP, m-PP and m-PP/nano-filler composites were sufficient to enhance the foaming behavior.

• Polymer(Korea)
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• v.38 no.4
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• pp.502-509
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• 2014

Carbon-based nanoplatelets such as graphene oxide (GO) sheets and graphite nanoplatelets (GNPs) are frequently used as conductive nanofillers for polymer nanocomposites. In this study, polystyrene (PS)/GO and PS/GNP nanocomposites were prepared through a latex technology and investigated to compare the effect of nanofillers on rheological and electrical properties of the PS nanocomposites. PS particles were prepared by emulsifier-free emulsion polymerization and GO was synthesized by using the modified Hummers' method from graphite. Hydrophilic GO was dispersed in aqueous PS suspension, but hydrophobic GNPs were dispersed with the help of a surfactant. In comparison with PS/GO nanocomposites, the rheological properties of PS/GNP counterparts were not too high because GNP existed in aggregates of graphene layers. Conducting pathways of PS/GO and PS/GNP nanocomposites were achieved at the electrical percolation threshold of 0.50 and 5.82 wt%, respectively. The reason for enhanced electrical conductivity in PS/GO nanocomposites is that GO was thermally reduced during molding.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.2
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• pp.131-136
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• 2023

Nanocomposites have been considered innovative composite materials that have multi-functionality and high performance. Because the incorporation of nanoscale fillers may significantly improve the electrical, mechanical, and thermal properties of composites, numerous extensive studies on the characterization of nanocomposites with nanoscale fillers have been performed. In particular, the development of nanocomposites using carbon-based nanoscale fillers (e.g., carbon nanotubes, carbon black, graphene nanoplates) have attracted much interest in the composite field. This paper provides a review of recent advances in the electrical/mechanical characteristics of nanocomposites, which are essential for their practical applications. Furthermore, this paper revisits the recent research on multi-scale modeling, which is a promising approach for predicting the characteristics of nanocomposites. The current challenges and future development potentials for multi-scale modeling are also discussed.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.1
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• pp.62-70
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• 2009

The objective of this study was to measure the leaching of filler (Si, Ba) from nanofiller-contained composites (Palfique Estelite $sigma^{{R}}$ (Tokuyama Dental Corp., Tokyo, Japan), $Z-350^{{R}}$ (3M ESPE, USA), Ceram X duo $E3^{{R}}$, $D3^{{R}}$ (Dentsply, Konstanz, Germany)) under different conditions. The samples used for the study of leachable components were made by insertion of the material into a circular mold, 10 mm in diameter and 3.0 mm high. Each specimen was placed in a disposable polystyrene vial containing 5 mL of distilled water, artificial saliva or 0.1N NaOH and kept in an oven at $37^{\circ}C$. ; water and artificial saliva - 150 days, 0.1N NaOH - 15days. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was used to determine the amount of Si and Ba in the test solutions. 1. Filler leaching was significantly great in 0.1N NaOH among all samples(p<.0.001). 2. When samples were stored in the distilled water, Estelite showed the lowest amount of Si leaching. When samples were stored in the artificial saliva, Z-350 showed the lowest amount of Si leaching. 3. There were significant differences in filler leaching between 3 storage medias and composite resins(p<.0.001). 4. Si and Ba leaching occurred in greater proportion when samples were stored in the artificial saliva than distilled water. 5. There were significant interactions in monthly filler leaching between leaching in artificial saliva and in distilled water, as well as the interaction between storage medium and filler(p<.0001). These results indicate that a continuous filler leaching of nanofiller-contained composite resins was in storing aqueous solutions under over time.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1141-1142
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• 2015

실리콘 고무는 옥외용 폴리머 애자 또는 부싱 등에 주로 사용되고 있으며, 이에 대한 연구가 많이 진행되어 지고 있다. 최근에는 나노 기술이 발달함에 따라 전기 재료에 나노 사이즈의 필러를 첨가하여 재료의 특정 특성들을 향상시키는 연구들이 진행되어 지고 있다. 본 논문에서는 전기적인 성능을 향상시키고자 나노 사이즈의 $Al_2O_3$를 첨가한 상온 경화형 실리콘 고무에 대한 연구를 진행하였으며, DC 전계와 오염 상황 하에서 연면 파괴 강도를 측정하였으며, 접촉각과 표면 저향률을 측정하였다. 실험 결과, 필러 함량이 증가할수록 연면 절연 파괴 강도와 표면 저항률은 증가하였으며 접촉각은 감소하였다. 또한, 일정 함량 이상에서는 연면 절연 파괴 강도와 표면 저항율이 감소하는 것으로 나타났다.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.3
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• pp.516-526
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• 2004

Polymerization shrinkage of photoinitiation type composite resin cause several clinical problems. The purpose of this study was to evaluate the shrinkage strain stress, linear polymerization shrinkage, compressive strength and microhardness of recently developed composite resins. The composite resins were divided into four groups according to the contents of matrix and filler type. Group I : $Denfil^{TM}$(Vericom, Korea) with conventional matrix, Group II : $Charmfil^{(R)}$(Dentkist, Korea) with microfiller and nanofller mixture, Group III : $Filtek^{TM}$ Z250(3M-ESPE, USA) TEGDMA replaced by UDMA and Bis-EMA(6) in the matrix, and Group IV : $Filtek^{TM}$ Supreme(3M-ESPE, USA) using pure nanofiller. Preparation of acrylic molds were followed by filling and curing with light gun. Strain gauges were attached to each sample and the leads were connected to a strainmeter. With strainmeter shrinkage strain stress and linear polymerization shrinkage was measured for 10 minutes. The data detected at 1 minute and 10 minutes were analysed statistically with ONE-way ANOVA test. To evaluate the mechanical properties of tested materials, compressive hardness test and microhardness test were also rendered. The results can be summarized as follows : 1. Filling materials in acrylic molds showed initial temporary expansion in the early phase of polymerization. This was followed by contraction with the rapid increase in strain stress during the first 1 minute and gradually decreased during post-gel shrinkage phase. After 1 minute, there's no statistical differences of strain stress between groups. The highest strain stress was found in group IV and followed by group III, I, II at 10 minutes-measurement(p>.05). In regression analysis of strain stress, group III showed minimal inclination and followed by group II, I, IV during 1 minute. 2. In linear polymerization shrinkage test, the composite resins in every group showed initial increase of shrinkage velocity during the first 1 minute, followed by gradually decrease of shrinkage velocity. After 1 minute, group IV and group III showed statistical difference(p<.05). After 10 minutes, there were statistical differences between group IV and group I, III(p<.05) and between group II and group III(p<.05). In regression analysis of linear polymerization shrinkage, group II showed minimal inclination and followed by group IV, III, I during 1 minute. 3. In compressive strength test, group III showed the highest strength and followed by group II, IV, I. There were statistical differences between group III and group IV, I(p<.05). 4. In microhardness test, upper surfaces showed higher value than lower surfaces in every group(p<.05).