• Title/Summary/Keyword: percolation threshold

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Charge Carrier Photogeneration and Hole Transport Properties of Blends of a $\pi$-Conjugated Polymer and an Organic-Inorganic Hybrid Material

  • Han, Jung-Wook;An, Jong-Deok;Jana, R.N.;Jung, Kyung-Na;Do, Jung-Hwan;Pyo, Seung-Moon;Im, Chan
    • Macromolecular Research
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    • v.17 no.11
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    • pp.894-900
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    • 2009
  • This study examined the charge carrier photogeneration and hole transport properties of blends of poly (9-vinylcarbazole) (PVK), $\pi$-conjugated polymer, with different weight proportions (0~29.4 wt%) of (PEA)$VOPO_4{\cdot}H_2O$ (PEA: phenethylammonium cation), a novel organic-inorganic hybrid material, using IR, UV-Vis, and energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA), steady state photocurrent (SSPC) measurement, and atomic force microscopy (AFM). The SSPC measurements showed that the photocurrent of PVK was reduced by approximately three orders of magnitude by the incorporation of a small amount (~12.5 wt%) of (PEA) $VOPO_4{\cdot}H_2O$, suggesting that hole transport occurred through the PVK carbazole groups, whereas a reverse trend was observed at high proportions (>12.5 wt%) of (PEA)$VOPO_4{\cdot}H_2O$, suggesting that transport occurred via (PEA)$VOPO_4{\cdot}H_2O$ molecules. The transition to a trap-controlled hopping mechanism was explained by the difference in ionization potential and electron affinity of the two compounds as well as the formation of charge percolation threshold pathways.

Study on Physical Properties of Waterborne Polyurethane and Carbon Nanofiber Composites (수분산 폴리우레탄 및 탄소나노섬유 복합체의 물리적 특성)

  • Lim, Suk-Dae;Ko, Sang-Choel;Kwac, Lee-Ku
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.20 no.11
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    • pp.24-29
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    • 2021
  • In this study, the electrical and mechanical properties of carbon polymer composites, which have been gradually increasing in use in various fields, were investigated, and environment-friendly carbon nanofiber/waterborne polyurethane composites were prepared. Carbon nanofibers (diameter = approximately 100-300 mm) were synthesized using a relatively simple CVD process, obtaining a carbon material for application in ultrathin planar heating films and EMP shielding films in the future. The carbon nanofiber was dispersed, and mixed with water-dispersible polyurethane using a dispersing aid. According to the carbon nanofiber mass ratio, 20%-60% polyurethane/carbon nanofiber composites were manufactured. At a concentration of approximately 20%, the percolation threshold was determined, and at a concentration of approximately 50%, an electrical conductivity greater than 0.1 S/cm was determined. Moreover, a sample having a concentration of up to 60% was evaluated to further understand the mechanical properties. It was observed that as the concentration of the carbon nanofibers increased, the elongation decreased.

Characteristics of Engineered Soils (Engineered Soils의 특성)

  • Lee, Jong-Sub;Lee, Chang-Ho;Lee, Woo-Jin;Santamarina, J. Caries
    • Journal of the Korean Geotechnical Society
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    • v.22 no.8
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    • pp.129-136
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    • 2006
  • Engineered mixtures, which consist of rigid sand particles and soft fine-grained rubber particles, are tested to characterize their small and large-strain responses. Engineered soils are prepared with different volumetric sand fraction, sf, to identify the transition from a rigid to a soft granular skeleton using wave propagation, $K_{o}-loading$, and triaxial testing. Deformation moduli at small, middle and large-strain do not change linearly with the volume fraction of rigid particles; instead, deformation moduli increase dramatically when the sand fraction exceeds a threshold value between sf=0.6 to 0.8 that marks the formation of a percolating network of stiff particles. The friction angle increases with the volume fraction of rigid particles. Conversely, the axial strain at peak strength increases with the content of soft particles, and no apparent peak strength is observed in specimens when sand fraction is less than 60%. The presence of soft particles alters the formation of force chains. While soft particles are not part of high-load carrying chains, they play the important role of preventing the buckling of stiff particle chains.

Effect of Surfactant on Rheological and Electrical Properties of Latex-Blended Polystyrene/Single-Walled Carbon Nanotube Nanocomposites (계면활성제가 라텍스 블렌딩 폴리스티렌/단일벽 탄소나노튜브 나노복합재료의 유변학적, 전기적 물성에 미치는 영향)

  • Kang, Myung-Hwan;Noh, Won-Jin;Woo, Dong-Kyun;Lee, Seong-Jae
    • Polymer(Korea)
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    • v.36 no.3
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    • pp.364-371
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    • 2012
  • Polystyrene/single-walled carbon nanotube (PS/SWCNT) nanocomposites were prepared by latex technology and the effect of surfactant (SDS) on nanotube dispersion, rheological and electrical properties was investigated. The nanocomposites were prepared through freeze-drying after mixing PS particles and aqueous SWCNT/SDS suspension. As the SDS content increased, the storage modulus and complex viscosity of the nanocomposites were increased due to enhanced dispersion of nanotubes, but if the content excessively increased, the modulus and viscosity began to decrease due to low molecular weight of SDS. The electrical conductivity sharply increased with the addition of SDS, and then did not show significant changes. This result is speculated to be the competition between the increased dispersion of nanotubes and the deterioration of electrical conductivity by SDS adsorption. An optimal ratio of SDS to SWCNT for improving electrical conductivity and end-use properties was 2. With this ratio, the electrical percolation threshold of SWCNT was less than 1 wt%.

A Novel Patterning Method for Silver Nanowire-based Transparent Electrode using UV-Curable Adhesive Tape (광경화 점착 테이프를 이용한 은 나노와이어 기반 투명전극 패터닝 공법)

  • Ju, Yun Hee;Shin, Yoo Bin;Kim, Jong-Woong
    • Journal of the Microelectronics and Packaging Society
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    • v.27 no.3
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    • pp.73-76
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    • 2020
  • Silver nanowires (AgNWs) intrinsically possess high conductivity, ductility, and network structure percolated in a low density, which have led to many advanced applications of transparent and flexible electronics. Most of these applications require patterning of AgNWs, for which photolithographic and printing-based techniques have been widely used. However, several drawbacks such as high cost and complexity of the process disturb its practical application with patterning AgNWs. Herein, we propose a novel method for the patterning of AgNWs by employing UV-curable adhesive tape with a structure of liner/adhesive layer/polyolefin (PO) film and UV irradiation to simplify the process. First, the UV-curable adhesive tape was attached to AgNWs/polyurethane (PU), and then selectively exposed to UV irradiation by using a photomask. Subsequently, the UV-curable adhesive tape was peeled off and consequently AgNWs were patterned on PU substrate. This facile method is expected to be applicable to the fabrication of a variety of low-cost, shape-deformable transparent and wearable devices.

Preparation, Morphology and Electrical Conductivity of Polystyrene/Polydopamine- Carbon Nanotube Microcellular Foams via High Internal Phase Emulsion Polymerization (고내상 에멀젼 중합에 의한 폴리스티렌/폴리도파민-탄소나노튜브 미세기공 발포체의 제조, 모폴로지 및 전기 전도도)

  • Kim, Haseung;Na, Hyo Yeol;Lee, Jong Heon;Lee, Seong Jae
    • Polymer(Korea)
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    • v.39 no.2
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    • pp.293-299
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    • 2015
  • Conductive microcellular foams consisted of polystrene (PS) and polydopamine-coated carbon nanotube (PDA-CNT) were prepared via high internal phase emulsion (HIPE) polymerization and their morphology and electrical conductivity were investigated. CNT as a conductive nanofiller was modified to PDA-CNT by coating with hydrophilic PDA on the surface of CNT to increase aqueous phase dispersion and emulsion stability. It was possible to prepare the HIPEs having higher PDA-CNT content and the resultant foams having improved conductivity due to its good dispersion. The foams showed the morphology of interconnected cell structure. As PDA-CNT content increased, yield stress and storage modulus increased and cell size reduced. The PDA-CNT content showing electrical percolation threshold was ca. 0.58 wt% and the conductivity at PDA-CNT content of 5 wt% was increased to $10^{-3}S/m$.

Evaluation of the Effect of Nickel Powder on the Piezoresistivity Behavior of Carbon-Fiber/Rubber Composites (탄소섬유/고무 복합재료의 압저항과 니켈입자의 영향)

  • Lim, Dong-Jin
    • Composites Research
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    • v.34 no.6
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    • pp.412-420
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    • 2021
  • In this study, we measure the initial electrical conductivity of SCF/rubber specimens and SCF/rubber specimens with nickel particles respectively. The corresponding electrical conductivity with compressive strain on the specimens is also measured. Through this experiment, we observed the effects of the volume fraction of carbon fiber, nickel particles and external strain on the electrical conductivity. Experiments show that even a small difference in the volume fraction of SCF plays a major role in the change of the electrical conductivity and that the piezoresistivity increases due to fiber reorientation respond to external strain. In addition, the nickel particles contribute to improving the electrical conductivity in specimens with carbon fibers above the threshold volume fraction. It was confirmed that there is an effect of offsetting the increment in the piezoresistivity caused by the reorientation of carbon fibers according to external strain.

Fabrication and Characterization of Hybrid NTC Thermistor Films with Conducting Oxide Particles by an Aerosol-Deposition Process (상온 분사 공정에 의한 산화물전도 입자 복합 하이브리드 NTC 서미스터 필름의 제작 및 특성)

  • Kang, Ju-Eun;Ryu, Jungho;Choi, Jong-Jin;Yoon, Woon-Ha;Kim, Jong-Woo;Ahn, Cheol-Woo;Choi, Joon Hwan;Park, Dong-Soo;Kim, Yang-Do
    • Journal of the Korean Ceramic Society
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    • v.50 no.1
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    • pp.63-69
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    • 2013
  • Negative-temperature coefficient (NTC) thermistors based on nickel manganite spinel ($NiMn_2O_4$) are widely used for many applications, such as sensors and temperature compensators, due to their good thermistor characteristics and stabilities. However, to achieve thermistors with a high NTC B constant, which is an important figure of merit pertaining to the degree of temperature sensitivity, the activation energy should be high such that high resistivity at ambient temperatures results. To obtain a high B constant and low resistivity, Al and Si modified spinel structured $Ni_{0.6}Si_{0.2}Al_{0.6}Mn_{1.6}O_4$ hybrid thick films with the conducting metal oxide of $LaNiO_3$ were fabricated on a glass substrate by aerosol deposition at room temperature (RT). The NTC-$LaNiO_3$ hybrid thick films showed resistivity as low as < $100k{\Omega}\;cm$ at $90^{\circ}C$, which is one or two orders of magnitude lower than that of the monolithic NTC films, while retaining a high B constant of $NiMn_2O_4$ of over 5500 K when 20 wt% $LaNiO_3$ was added without a post-thermal treatment. These phenomena are explained by the percolation threshold mechanism.

Characterization of FeCo Magnetic Metal Hollow Fiber/EPDM Composites for Electromagnetic Interference Shielding (FeCo 자성 금속 중공형 섬유 고분자 복합재의 전자파 차폐 특성 연구)

  • Choi, Jae Ryung;Jung, Byung Mun;Choi, U Hyeok;Cho, Seung Chan;Park, Ka Hyun;Kim, Won-jung;Lee, Sang-Kwan;Lee, Sang Bok
    • Composites Research
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    • v.28 no.6
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    • pp.333-339
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    • 2015
  • Electromagnetic interference shielding composite with low density ($1.18g/cm^3$) was fabricated using electroless plated FeCo magnetic metal hollow fibers and ethylene propylene diene monomer (EPDM) polymer. Aspect ratio of the fibers were controlled and their hollow structure was obtained by heat treatment process. The FeCo hollow fibers were then mixed with EPDM to manufacture the composite. The higher aspect ratio of the magnetic metal hollow fibers resulted in high electromagnetic interference shielding effectiveness (30 dB) of the composite due to its low sheet resistance (30 ohm/sq). The enhanced electromagnetic interference shielding effectiveness was mainly attributed to the formation of conducting network over the percolation threshold by high aspect ratio of fibers as well as an increase of the reflection loss by impedance mismatch owing to low sheet resistance, absorption loss, and multiple internal reflections loss.