• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.19.1-19.1
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• 2011

Effects of particle size, crystal structures and multilayer structures of $ATiO_3$, $ATa_2O_6$, $ANb_2O_6$, $AWO_4$, and $AMoO_4$ (A=Ni, Mg, Zn, Co) ceramic fillers on the dielectric properties of polystyrene (PS), polypropylene (PP) and polytetrafluoroethylene (PTFE) polymer matrices were investigated at microwave frequencies. The microwave dielectric properties of $ATiO_3$ (ilmenite), $ATa_2O_6$ (tri-rutile), $ANb_2O_6$ (columbite), AWO4 (wolframite), and AMoO4 (wolframite) ceramics were largely dependent on the structural characteristics of oxygen octahedra. The dielectric constant (K) of the composites was increased with the ceramic content. However, the dielectric loss (tan ${\delta}$) of the composites was affected by the type of ceramics and the crystallinity of polymers. For the composites with same amount of ceramics, the K was decreased and the tan ${\delta}$ was increased with the particle size of ceramics. Also, the dielectric properties of the composites were dependent on the multilayer structures with different arrangements. Several theoretical models have been employed to predict the effective dielectric properties of the composites. The frequency dependence of dielectric properties and the temperature coefficient of resonant frequency (TCF) of the composites were also discussed.

• 대한기계학회논문집A
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• 제33권3호
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• pp.261-264
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• 2009

We present a three-dimensional (3D) particle focusing channel using the positive dielectrophoresis (pDEP) guided by a dielectric structure between two planar electrodes. The dielectric structure between two planar electrodes induces the maximum electric field at the center of the microchannel, and particles are focused to the center of the microchannel by pDEP as they flow from the single sample injection port. Compared to the previous 3D particle focusing methods, the present device achieves the simple and effective particle focusing function without any additional fluidic ports and top electrodes. In the experimental study, approximately 90 % focusing efficiency were achieved within the focusing length of 2mm, on both x-z plane (top-view) and y-z plane (side-view) for $2{\mu}m$-diameter polystyrene (PS) bead at the applied voltage over 15 Vp-p (square wave) and at the flow rate below 0.01 ${\mu}l$/min. The present 3D particle focusing channel results in a simple particle focusing method suitable for use in integrated microbiochemical analysis system.

• 대한기계학회논문집A
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• 제25권5호
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• pp.816-822
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• 2001

The thermoforming process is widely used in the plastics industry to produce articles for the packaging, automotive, domestic construction and leisure industries. The microcellular foaming process appeared at M.I.T. in 1980s to save a quantity of polymer materials and increase their mechanical properties. The glass transition temperature of polymer materials is one of many important process variables in appling the microcellular foaming process to the conventional thermoforming process. The goal of this research is to evaluate the relation between gas absorption and glass transition temperature in batch process using microcellular foaming process. The weight gain ratio of polymer materials has a conception of gas absorption. Polymers such as acrylonitrile-butadiene-styrene(ABS), polystyrene(PS) have been used in this experiment. According to conventional Chows model and Cha-Yoon model, it was estimated with real experimental result to predict a change of glass transition temperature as a function of the weight gain ratio of polymer materials in batch process to gain microcellular foamed plastic products.

• 한국전기전자재료학회논문지
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• 제16권11호
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• pp.1055-1061
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• 2003

A study has been made of surface modification of various organic materials by ion implantation to increase the surface electrical properties. The substrate used were PP(polypropylene), PET(polyethylene teraphthalate), ECOP(ethylene copolyester), PS(polystyrene). N$_2$, Ar ion implantation was performed at energies of 40 and 50keV with fluences from 5${\times}$ 10$\^$15/ to 7${\times}$10$\^$16/ ions/$\textrm{cm}^2$ with and without H$_2$O gas environment. Surface resistance decrease of implanted polymers was affected by ion implantation energy, ion species, atmosphere of chamber and kind of polymer. In result, surface conductivity of polymers irradiated with atmosphere gas H$_2$O was 10 times more higher than normal vacuum atmosphere, but after 90 hours, surface conductivity returned to the without H$_2$O gas atmosphere condition caused by aging effect. After vacuum forming, surface resistance value was changed to over 10$\^$16/$\Omega$/$\square$, because creation of surface cracks.

• 반도체디스플레이기술학회지
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• 제11권1호
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• pp.21-27
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• 2012

The optical diffuser for direct-lit LED backlight unit was prepared by using extrusion compounding followed by thermoforming process. Poly(methyl methacrylate) (PMMA) with superior optical characteristics and polycarbonate (PC) with good thermal property were used as base resins, and crosslinked polystyrene (PS) and PMMA beads as diffusing agents were incorporated into resin matrix to derive light scattering and diffusing action. In the compounded plate, the diffusing beads were observed to be dispersed uniformly and distinctly in the continuous phase. The inclusion of polymeric beads up to 3 wt% substantially enhanced the optical characteristics such as luminance, luminance uniformity, haze for the diffuser. Two different diffusers of PC and PMMA-based compound with various compositions were compared in terms of measured optical, thermal, and mechanical properties, which would be expected to be utilized for the industrial application of LED backlight unit.

• Macromolecular Research
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• 제16권1호
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• pp.21-30
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• 2008

Based on the sheath-core bicomponent composite fibers with modified polystyrene (PS) and the modified polypropylene (PP), composite fibers obtained were further cross-linked and sulphonated with chlorosulphonic acid to produce strong acidic cation ion exchange fibers. The structures of the fibers obtained were characterized using Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC) etc. The optimal technology of the fibers obtained is discussed. The static absorption capacity of the sheath-core bicomponent composite cation exchange fibers for $Zn^{2+}$, $Cu^{2+}$ was determined. The absorption kinetics and major factors affecting the absorption capacities of $Zn^{2+}$, $Cu^{2+}$ were studied, and its chemical stability and regenerating properties were probed. The results suggest that cation exchange fibers with better mechanical properties and higher exchange capability were obtained. Moreover, this type of ion exchange fiber has good absorption properties and working stability to various metal ions. Hence, they have higher practicability.

• 한국물환경학회지
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• 제28권5호
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• pp.669-675
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• 2012

Recently, there have been active researches regarding endocrine-disrupting chemicals (EDCs). In this study, fifteen small freshwater streams in Cholla-namdo province, South Korea were investigated with respect to the concentration of the endocrine disruptors - Bisphenol A (BPA), styrene monomer (SM), styrene dimer (SD), and styrene trimer (ST) by gas chromatography-mass spectrometry (GC-MS). Measured concentration of the target compounds in the sampled water ranged from

• Bulletin of the Korean Chemical Society
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• 제28권6호
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• pp.1015-1020
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• 2007

A simple approach to prepare arrays of Au/TiO2 composite nanoparticles by using Au-loaded block copolymers as templates combined with a sol-gel process is described. The organic-inorganic hybrid films with closely packed inorganic nanodomains in organic matrix are produced by spin coating the mixtures of polystyrene-block-poly(ethylene oxide) (PS-b-PEO)/HAuCl4 solution and sol-gel precursor solution. After removal of the organic matrix with deep UV irradiation, arrays of Au/TiO2 composite nanoparticles with different compositions or particle sizes can be easily produced. Different photoluminescence (PL) emission spectra from an organic-inorganic hybrid film and arrays of Au/TiO2 composite nanoparticles indicate that TiO2 and Au components exist as separate state in the initial hybrid film and form composite nanoparticles after the removal of the block copolymer matrix.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.279-279
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• 2010

Smart gels have recently associated with photonic crystals to form photonic gels. Since these photonic gels are capable of reversibly converting the volume change of gels induced in response to external chemical or electric stimuli into characteristic optical signals, they have been considered not only as a good platform for label-free chemical or biological detection, actuators or optical switches but also as a good model system to investigate gel swelling behaviour. Recently, we reported block copolymer photonic gels self-assembled from polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) block copolymers, and demonstrated that selective swelling of lamellar structure allows extremely large tunability of the photonic stop band from UV region to IR region ($\lambda$ peak=350~1,600 nm). Herein we report block copolymer photonic gels which exhibit strong tunable optical hysteresis and their applications. As nonlinear responses in swelling of hydrogels were often observed, photonic gels exhibit optical hysteresis with change of external pH. We demonstrate such optical hysteresis can be precisely programmed by controlling ion-pairing affinity. We anticipate that photonic gels with carefully tunned optical hysteresis are applicable to optical memory devices.

• Macromolecular Research
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• 제16권3호
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• pp.261-266
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• 2008

A variety of end-functionalized polymers were grafted spontaneously onto multi-walled carbon nano-tubes (MWNTs) using a solution mixing process. The end-functional groups of the polymers underwent noncovalent grafting to the defect sites at the surface of the purified MWNTs through zwitterionic interaction or hydrogen bonding. The physically grafted polymers including polystyrene (PS), poly(methyl methacrylate) (PMMA), polyethylene oxide (PEO), and polydimethylsiloxane (PDMS) provided sufficient compatibility with an organic solvent or polymer matrix, such that the nanotubes could be finely dispersed in various organic media. This approach is universally applicable to a broad range of polymer-solvent pairs, ensuring highly dispersed carbon nanotubes through simple solution mixing.