• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.273-276
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• 2008

Thermoplastic resin takes place stress relaxation and creep according to temperature and time. In room temperature, time dependent deformation (TDD) of polymer was carried out at previous study. In this study, it evaluates time dependent deformation to relate temperature. Nanoscale indents can be used as cells for molecular electronics and drug delivery, slots for integration into nanodevices, and defects for tailoring the structure and properties. Therefore, it is important to control pattern depth for change of indent depth by creep when using Nanoindenter. For evaluating TDD at high temperature, it is occurred thermal-nanoindentation test by changing hold time at maximum load. Temperature is putted at $90^{\circ}C$, hold time at maximum loads are putted at 1, 10, 50, 100, 200, 300 and 500s.

• Journal of Adhesion and Interface
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• v.4 no.4
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• pp.22-27
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• 2003

Chemical modification of carbon nanotube (CNT) was carried out using $HNO_3$ and $H_2SO_4$ and characterized by analyzing the CNT before and after the modification using FT-IR and titration. Aggregation behaviors were investigated using a real-time video microscope after the chemically modified CNT(mCNT) had been dispersed in organic solvents such as toluene, dimethylformamide (DMF) and N-methylpyrrolidone (NMP) by ultrasonication. The mCNT showed better dispersion in polar sovents of DMF and NMP than the rCNT. CNT/ poly(methylmethacrylate) (PMMA) films were prepared from solution DMF/PMMA solutions. The films containing mCNT also revealed the improved dispersion.

• Polymer(Korea)
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• v.26 no.1
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• pp.37-44
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• 2002

The polymer blends of waste polyvinyl chloride (RPVC) and waste polyethylene(RPE) were prepared by melt mixing, and their morphology and tensile properties were evaluated after the copolymers having an ethylene group in backbone and ester group in side position were added as comptatibilizers. The blend compositions were varied as follows ; RPVC/RPE 85/15 wt%, where RPVC formed a continuous phase : 50/50, mid composition : 15/85, RPE a continuous phase. The blends revealed a very low compatibility between component polymers because they showed domain sizes greater than $10\mu\textrm{m}$ over all compositions, especially the worst compatibility around mid composition. The blends showed higher compatibility when ethylene vinylacetate copolymer(EVA) and ethylene ethylacrylate-graft-methyl methacrylate copolymers(EEA-MMA) were added.

• Composites Research
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• v.17 no.1
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• pp.10-17
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• 2004

In this work, the blend system prepared from epoky(DGEBA)/polymethylmethacrylate(PMMA) was investigated in thermal and mechanical interfacial property measurements. The thermal properties were carried out by DSC, DMA, and TGA measurements. Also, the surface free energy and fracture toughness were determined by contact angle and critical stress intensity factor($K_{IC}$), respectively. And the fracture surface was observed by SEM after $K_{IC}$ tests. As experimental results, the curing temperature and glass transition temperature were slightly increased in addition of PMMA. Surface free energy of the blends showed an improved value at low contents of PMMA which could be attributed to the both increasings of London dispersive and polar components. From measurement of $K_{IC}$ of the blends, the highest value was found at 5 phr. This was due to the increasing of compatibility or physical interaction in macromolecular chains between DGEBA and PMMA of the blends.

• Applied Chemistry for Engineering
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• v.17 no.4
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• pp.397-402
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• 2006

We have investigated the effect of each ingredient in the light diffusing film (LDF) which was used as backlight unit (BLU) of TFT-LCD TV on physical, electrical, thermal and optical properties of LDF. In anti-blocking layer, the excellent anti-blocking ability was obtained when 0.5~1.5 wt% of acrylic bead was added, and good decay-time and water-stability were shown when 0.8 wt% of tertiary ammonium salt was added. Optimal results for adhesion strength, curing rates and flexibility on the surface of PET film have been obtained in the light diffusing layer by using acrylic polyol as a binder resin, and by addition of 30~35 wt% non-yellowing type HDI crosslinker. In addition, the highest normal luminance value was obtained by addition of 250 wt% poly-dispersive polystyrene ($20{\mu}m$ PS) and polymethylmethacrylate ($20{\mu}m$ PMMA) beads into the binder resin (100 wt%). The higher normal luminance could be got for PMMA beads than PS beads because of the transmittance difference.

• Polymer(Korea)
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• v.30 no.4
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• pp.332-337
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• 2006

Monodisperse polymer particles were prepared via one-step seeded polymerization using PMMA seed particles and HDDA (or EGDMA) as crosslinking monomer. For the study, the effects of 1) the ratio of the absorbed monomer or monomer mixture to the seed polymer particles (swelling ratio), 2) the ratio of EGDMA in absorbed monomer mixture, 3) the dosage of initiator, and 4) electro less Ni plating on the variation of mechanical properties of monodisperse polymer particles, such as recovery rate, K-values, breaking strength and breaking displacement, were investigated by using MCT (micro compression test). It was observed that monomer swelling ratio influenced only breaking strength, but EGDMA ratio in monomer mixture, dosage of initiator and electroless Ni plating affected both K-values and breaking strength.

• Journal of the Korean Electrochemical Society
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• v.11 no.2
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• pp.125-129
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• 2008

Rechargeable lithium-ion polymer batteries have been considered to be next-generation power sources for portable electronic devices and electric vehicles. In this work, we tried to improve the cycling performances of lithium-ion polymer cells by coating aluminum fluoride and acrylonitrile-methyl methacrylate copolymer to the polyethylene separator. It was found that the addition of aluminum fluoride to the surface-modified separator reduced the interfacial resistances and thus the cell exhibited a less capacity fading and better high rate performance. The cell showed an initial discharge capacity of 150 mAh/g and good capacity retention at 0.5 C rate.

• Composites Research
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• v.30 no.4
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• pp.247-253
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• 2017

In this study, the mechanical behavior and interface properties of boron nitride nanotube-poly(methyl methacrylate) nanocomposites are predicted using the molecular dynamics simulations and the double inclusion model. After modeling nanocomposite unit cell embedding single-walled nanotube and polymer, the stiffness matrix is determined from uniaxial tension and shear tests. Through the orientation average of the transversely isotropic stiffness matrix, the effective isotropic elastic constants of randomly dispersed microstructure of nanocomposites. Compared with the double inclusion model solution with a perfect interfacial condition, it is found that the interface between boron nitride nanotube and polymer matrix is weak in nature. To characterize the interphase surrounding the nanotube, the two step domain decomposition method incorporating a linear spring model at the interface is adopted. As a result, various combinations of the interfacial compliance and the interphase elastic constants are successfully determined from an inverse analysis.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.3
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• pp.36-42
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• 2015

The aspherical lens was designed to be able to array a focal point. For this reason, it has very curved surface. The aspherical lens is fabricated by injection molding or diamond turning machine. With the aspherical lens, tool marks and surface roughness affect the optical characteristics, such as transmissivity. However, it is difficult to polish free form surface shapes uniformly with conventional methods. Therefore, in this paper, the ultra-precision polishing method with MR fluid was used to polish an aspherical lens with 4-axis position control systems. A Tool path and polishing mechanism were developed to polish the aspherical lens shape. An MR polishing experiment was performed using a generated tool path with a PMMA aspherical lens after the turning process. As a result, surface roughness was improved from $R_a=40.99nm$, $R_{max}=357.1nm$ to $R_a=4.54nm$, $R_{max}=35.72nm$. Finally, the MR polishing system can be applied to the finishing process of fabrication of the aspherical lens.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.1
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• pp.92-99
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• 2014

An aspherical lens, which resolves several problems with a spherical lens,typically serves asa key part of an optical system. Generally, an aspherical lens is fabricated using a diamond turning machine or by mean of injection molding. However, residual stress and/or tool marks can arise when using a commercial fabricating method such as DTM or injection molding. A polishing process, thus, is commonly used to obtain a high-precision aspherical lens. In this study, a polishing method using MR fluid was applied to minimize several problems, in this case residual stress and the creation of tool marks, during the cutting process. The MR polishing system was developed to polish aspherical lenses. A series of experiments were performed to obtain a very fine surface roughness. PMMA (the lens material for molding) was used as a workpiece, and the gap size, magnetic field intensity, wheel speed and feed rate were selected as the parameters in this study. Finally, a very fine surface roughness of Ra=2.12nm was obtained after MR polishing.