• Composites Research
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• v.19 no.5
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• pp.28-33
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• 2006

In this paper, we have studied the complex permittivities and their influence on the design of microwave absorbers of E-glass fabric/epoxy composite laminates containing three different types of carbon-based nano conductive fillers such as carbon black (CB), carbon nano fiber (CNF) and multi-wall nano tube (MWNT). The measurements were performed fur permittivities at the frequency band of 0.5 GHz$\sim$18.0 GHz using a vector network analyzer with a 7 mm coaxial air line. The experimental results show that the complex permittivities of the composites depend strongly on the natures and concentrations of the conductive fillers. The real and imaginary parts of the complex permittivities of the composites were proportional to the filler concentrations. But, depending on the types of fillers and frequency band, the increasing rates of the real and imaginary parts with respect to the filler concentrations were all different. These different rates can have an effect on the thickness in designing the single layer microwave absorbers. The effect of the different rates at 10 GHz was examined by using Cole-Cole plot; the plot is composed of a single layer absorber solution line and measured permittivities from these three types of composites. Single layer absorbers of 3 different thicknesses using carbon nano materials were fabricated and the -10 dB band of absorbing performances were all about 3 GHz.

• Macromolecular Research
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• v.8 no.1
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• pp.34-43
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• 2000

The melt rheology of four binary blends of ethylene 1-octene copolymers (EOCs) which consist of one component by Ziegler-Natta and another by metallocene catalysts, was studied to elucidate miscibility in the melt by using torsion rheometer at 200$\^{C}$ and different shear rates. The four blend systems, designated into the FA+FM, SF+FM, RF+EN, and RF+PL blend, are divided and interpreted based on the melt index (MI), the density and the comonomer contents. The melt viscosity such asη', η", and η$\^$*/ is weight average value if the comonomer contents are similar, otherwise they show different manner. The experimental resole are analyzed based on the Cole-Cole plot of logη' uersus log η", the logarithmic plots of the dynamic storage modulus (G') versus the dynamic loss modulus (G") for various blend compositions, and the melt viscosity of 11', n", and f" as a function of blend compositions. As a cerise-quence, the FA+FM blend is miscible, but the SF+FM, RF+EN, and RF+PL blends are not in the melt. Thus miscibility of the blends studied in this communication is suggested to strongly influence by the comonomer contents rather than the density or the MI.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.258.1-258.1
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• 2015

ITO가 코팅된 PET 기판 위에 P3HT:PCBM으로 이루어진 bulk heterojunction 유기 태양전지 소자를 만들었다. 이렇게 만들어진 유기 태양전지의 flexibility 특성을 측정하기 위해서, 태양전지 소자를 반지름이 다른 원통에 감아서 휘어지게 한 후 AM 1.5의 조명 하에서 전류-전압 특성을 관측하고 소자의 임피던스 분석도 측정하였다. 이때 flexibility 특성 측정의 일관성을 위하여, 단 하나의 유기 태양전지 소자를 만들고, 이 소자를 반지름이 큰 원통에서 부터 휘게 하고난 후 소자의 특성을 측정하고, 점차 작은 원통으로 바꾸어 가면서 측정을 진행하였다. 임피던스 분석 실험 자료로부터 shifted two semicircles이라는 equivalent circuit model를 분석하고 난 후, 이 회로를 구성하는 구성 성분-R(s), R(low f), R(hi f), C(low f), C(hi f)-값의 변화를 원통의 반지름의 변화에 따라 분석하였다. 반지름이 0.75cm일 때, power conversion efficiency (PCE) 값은 초기값에 비해 약 1/3로 줄었고, 반지름이 0.5cm일 때는 약 10%로 줄어 들었다. 나머지 1~2 cm일 때는 거의 변화가 나타나지 않았다. 휘어짐에 따른 이러한 태양전지의 특성의 변화를 임피던스 분석의 Cole-Cole plot의 저 주파수 영역의 반원의 반지름에 가장 큰 영향을 받음을 확인하였고, 저항과 capacitance 값의 변화에 따른 특성에 대해 이번 발표에서 더 자세히 설명할 예정이다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.309-310
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• 2006

We studied dielectric properties of OLEDs(Organic Light-emitting Diodes) depending on applied voltage (AC) of PTFE(Polytetrafluoroethylene), material of hole injection layer in structure of ITO/hole injection layer (PTFE)/emitting layer, Alq3(Tris(8-hydroxyquinolibe) Alumin)/Al. PTFE is deposited 2 [nm] as rate of 0.2~03 [${\AA}/s$] and $Alq_3$ is deposited 100 [nm] as rate of 1.3~1.5 [${\AA}/s$] m high vacuum ($5{\times}10^{-6}$[torr]). In result of these studies, we can know dielectric properties of OLEDs. Impedance is decreased depending on applied voltage variation, dielectric loss showed peak in specified voltage and showed cole-cole plot of a specimen.

• Journal of Korea Multimedia Society
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• v.19 no.7
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• pp.1146-1153
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• 2016

The bioelectrical impedance (BI) at the inner forearms was measured using bioelectrical impedance measurement system (BIMS), which employs the multi-frequency and the two-electrode method. Experiments were performed as follows. First, while applying a constant alternating current of 800A to the inner region of the forearms, BI (Z) was measured at nineteen frequencies ranging from 5 to 500 kHz. The prediction marker (PM) was calculated for right and left forearm. The resistance (R) and the reactance (X_c) were simultaneously measured during impedance measurement. Second, a Cole-Cole plot (relationship between reactance and resistance) was obtained for left and right forearm, indicating the different characteristic frequencies (f_c). Third, the phase angle was obtained, indicating strong dependence on the applied frequency.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.04a
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• pp.5-8
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• 2004

We have investigated equivalent-circuit analysis of organic light-emitting diodes using frequency-dependent response of $ITO/Alq_3(60nm)/Al$ device at two different bias voltages. Complex impedance Z of the device was measured in the frequency range of 40Hz~1MHz. A Cole-Cole plot shows that there are two dielectric relaxations at the bias below turn-on voltage, and one relaxation at the bias above turn-on voltage. We are able to interpret the frequency-dependent response in terms of equivalent-circuit model of contact resistance $R_s$ in series with parallel combination of resistance $R_p$ and capacitance $C_p$. We have obtained contact resistance $R_s$ around $90{\Omega}$, mainly from the ITO anode.

• Polymer(Korea)
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• v.31 no.5
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• pp.399-403
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• 2007

Trans-esterification behavior of polycarbonate/poly(butylene terephthalate) (PC/PBT) blends was investigated during the melt mixing process. Rheological and fracture behaviors, and fracture morphology were also investigated as a function of PC/PBT blend ratio. Based on FT-IR and $^1H-NMR$ results, a trans-esterification reaction was confirmed to occur between PC and PBT during the melt mixing process. The melt index(MI) decreased with increased PC content, indicating the higher flow resistance of PC. The storage and loss moduli were increased by increasing the PC loading, and the PC/PBT blends were rheologically incompatible based on the Cole-Cole plot. The tensile property increased linearly with the increased PC content. However, the impact strength increased until 50 wt% of PC loading, notably around $30{\sim}40wt%$, and then was levelled off at 50 wt%. Rough ridges were formed on the impact fracture surfaces above the 40 wt% of PC content, supporting the observed higher impact strength in this range.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.178-178
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• 2008

ZnO 바리스터는 인가되는 전압에 따라 저항이 변하는 전압 의존형 저항체이며 각종 전기 전자 정보통신용 제품에 정전기(ESD) 대책용 소자로 폭 넓게 사용되는 전자 세라믹스 부품이다. 특별히 Bi-based ZnO 바리스터는 다양한 상(phase)으로 구성되어 있으며 그 입계의 전기적 특성은 소량 첨가되는 dopant의 종류에 따라 다양하게 변하는 것으로 알려져 있다. 본 연구에서는 Bi-based ZnO 바리스터 (ZnO-$Bi_2O_3$, ZnO-$Bi_2O_3-Mn_3O_4$)에서 각종 유전함수$(Z^*,M^*,\varepsilon^*,Y^*,tan{\delta})$를 이용하여 입계의 주파수-온도에 대한 특성을 살펴 보았다. 일반적인 ZnO 바리스터 제조법으로 시편을 제작하여 78K~800K 온도 범위에서 각종 유전함수를 이용하여 복소 평면도(complex plane plot)와 주파수 응답도(frequency explicit plot)의 방법으로 defect level과 입계 특성(활성화 에너지, 정전용량, 저항, 입계 안정성 등)에 대하여 고찰하였다. ZnO-$Bi_2O_3$(ZB)계와 ZnO-$Bi_2O_3-Mn_3O_4$(ZBM)계 모두 상온 이하의 온도에서 $Zn_i$와 $V_o$의 결함이 나타났으며, 이들의 결함 준위는 각 유전함수에 따라 다소 차이가 났다. 입계 특성으로 ZB계는 이상구간(560~660K)을 전후로 1.15 eV $\rightarrow$ 1.49 eV의 활성화 에너지의 변화가 나타났지만, ZBM계는 이러한 현상이 나타나지 않았다. 또한 입계 전위 장벽의 온도 안정성에 대해서는 Cole-Cole model을 적용하여 분포 파라미터 (distribution parameter; $\alpha$)를 구하여 고찰하였다. ZB계의 입계 안정성은 온도에 따라 불안정해 졌지만, ZBM계는 안정하였다.

• Polymer(Korea)
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• v.31 no.3
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• pp.269-272
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• 2007

In this study, we investigated the effects of electron beam irradiation on the rheological properties of PLA for enhancing processability. The electron beam was irradiated onto the pure PLA, chemically modified PLA by reactive extrusion, and PLA containing functional monomer. The complex viscosity and log G'vs. log G" plot among dynamic rheological properties were chosen for comparison. The complex viscosity of irradiated pure and chemically modified PLA decreased significantly due to de-gradation of PLA molecules with increasing the E-beam dosages. Complex viscosity of irradiated PLA with functional monomer showed maximum value at moderate dosage, while at high dosage the complex viscosity was decreased by a prolonged irradiation.

• Polymer(Korea)
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• v.34 no.5
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• pp.485-489
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• 2010

Poly(lactic acid)(PLA) has been modified by electron radiation in the presence of 5 phr glycidyl methacrylate (GMA) to enhance the melt strength of PLA. The modified PLA was prepared by varying the dose of irradiation and was characterized by observing the thermal properties, the melt viscoelastic properties and the gel fraction. The irradiated PLA with 300 kGy in the presence of 5 phr GMA showed drastically improved complex viscosity and storage modulus properties: a complex viscosity of about 210 times higher and a storage modulus of 14500 times higher than those of virgin PLA when measured at a frequency of 0.1 rad/s. Gel fraction study revealed that a branching reaction was more dominant than a crosslinking reaction when the PLA was irradiated with less than 200 kGy.