• Elastomers and Composites
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• 제47권1호
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• pp.75-81
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• 2012

주단량체로 에틸 아크릴레이트, 부틸 아크릴레이트, 메톡시에틸 아크릴레이트, 가교 단량체로 글리시딜 메타아크릴레이트를 유화중합하여 아크릴고무를 제조한 후, 가교제로써 2,2-bis[4-(4-aminophenoxy)phenyl]propane를 첨가하여 고무컴파운드를 제조하였다. 주단량체의 조성에서 에틸 아크릴레이트의 함량이 증가하면 내열성이 증가하는 경향을 보였는데 이는 아크릴고무의 유리전이온도가 감소되었기 때문이다. 또한 에틸 아크릴레이트의 에스테르 그룹 농도가 3개의 주단량체 중 가장 높기 때문에 에틸 아크릴레이트 함량이 증가할수록 내유성이 향상되었다. 2,2-Bis[4-(4-aminophenoxy)phenyl]propane의 함유량에 따른 영향은 2 phr 첨가까지 인장강도와 신장율은 증가하지만, 그 이상의 첨가에서는 가교밀도의 증가에 따른 점성과 탄성이 감소하여 그 값들이 감소하였다.

• Nuclear Engineering and Technology
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• 제44권1호
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• pp.61-70
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• 2012

In this study, a simple post-reconstruction dual-energy computed tomography (CT) method is proposed. A dual-energy CT algorithm for monochromatic x-rays was adopted and applied to the dual-energy CT of polychromatic x-rays by assigning a representative mono-energy. The accuracy of algorithm implementation was tested with mathematical phantoms. To test the sensitivity of this algorithm to the inaccuracy of representative energy value in energy values, a simulation study was performed with mathematical phantom. To represent a polychromatic x-ray energy spectrum with a single-energy, mean energy and equivalent energy were used, and the results were compared. The feasibility of the proposed method was experimentally tested with two different micro-CTs and a test phantom made of polymethyl methacrylate (PMMA), water, and graphite. The dual-energy calculations were carried out with CT images of all possible energy pairs among 40, 50, 60, 70, and 80 kVp. The effective atomic number and the electron density values obtained from the proposed method were compared with theoretical values. The results showed that, except the errors in the effective atomic number of graphite, most of the errors were less than 10 % for both CT scanners, and for the combination of 60 kVp and 70 kVp, errors less than 6.0 % could be achieved with a Polaris 90 CT. The proposed method shows simplicity of calibration, demonstrating its practicality and feasibility for use with a general polychromatic CT.

• Journal of Preventive Medicine and Public Health
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• 제47권3호
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• pp.169-176
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• 2014

Objectives: This study aimed to evaluate occupational symptoms and chemical exposures of nail salon technicians. Methods: Work-related symptoms of nail salon technicians in Daegu City were surveyed using a researcher-administered questionnaire, and responses were compared to those of non-exposed office workers as controls. Personal exposure level of airborne volatile organic compounds was also monitored using passive samplers. Results: A total of 159 subjects in 120 salons were interviewed. Average work-shift concentrations of 13 chemicals were measured for 50 workers from 30 salons using personal passive samplers. The most frequently reported respiratory or neurologic symptoms by nail shop technicians compared to controls were nose irritation (odds ratio [OR], 54.0; confidence interval [CI], 21.6 to 134.8), followed by headache (OR, 9.3; CI, 4.7 to 18), and throat irritation (OR, 4.3; CI, 2.2 to 8.5). For eyes and skin, 92% of respondents complained eye irritation (OR, 13.1; CI, 5.7 to 30.1). In musculoskeletal symptoms, workers reported pain or discomfort in shoulders (OR, 20.3; CI, 7.7 to 54) and neck (OR, 19.7; CI, 8.9 to 43.6). From personal measurements, the proportion of exceeding the Korean Occupational Exposure Limit was the highest for acetone with 64%, followed by toluene (50%), butyl acetate (46%), and methyl methacrylate (12%). However, the service was being provided without a proper ventilation system in most surveyed shops. Conclusions: Based on these findings, it is warranted to have appropriate local exhaust ventilation place to ensure adequate health protection of nail shop technicians as well as customers. At the same time, greater policy interests are warranted in nail care business to protect health of both workers and customers.

• Tribology and Lubricants
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• 제34권2호
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• pp.60-66
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• 2018

Graphene is a monolayer of carbon atoms (approximately 0.34 nm), arranged in a honeycomb network. It has been hailed as a next-generation flexible and transparent material because it has high electrical and thermal conductivities, excellent mechanical properties, as well as flexible and transparent properties. The wettability of graphene alters its adhesion or surface energy, and it is therefore an important parameter influencing its application in the fabrication of next-generation flexible and transparent electronics. Studies on the wettability of graphene are numerous and various opinions exist. However, almost all of these studies use the wet transfer method to transfer the graphene. In this study, therefore, we investigated the effect of wet and dry transfer methods on water contact angles of graphene on a substrate. The contact angles of substrates vary depending on the type of substrate. It was found that after graphene is transferred to the substrate, regardless of transfer method, the graphene/substrate contact angle increases to a value. The contact angle of graphene transferred using the dry transfer method is higher than the contact angle of graphene transferred using wet transfer methods. The wet transferred graphene is affected by the poly(methyl methacrylate) (PMMA) residue and the polar surface of substrate. The dry transferred graphene is influenced by the conformal contact between graphene and substrate.

• 소성∙가공
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• 제14권3호
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• pp.282-290
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• 2005

Nowadays, TFT-LCD is widely used as display unit of many digital devices. And, the backlight unit(BLU) is used as a light source of TFT-LCD module. In the backlight unit, the most important component is a light guide, which guides the input light to the TFT-LCD module uniformly. Recently, many researchers have focused on improving the efficiency of BLU by changing the design and structure of a light guide. In the present paper, a series of simulation was performed to find the optimal luminance distribution of emanated light from the given geometry as the first step. From the results of simulations for the light guide with given V-groove pattern, the emanated light from it is mostly affected by the groove angle. In the case of acute angle, about 74 degrees was found as optimal angle to satisfy the restrictions of angular luminance distribution, FWHM, the maximum luminance, etc. However, as far as the average luminance value was concerned, the case of 120 degrees(abtuse angle) was found to be the best while prism films were added to the BLU. As a next step the light guide samples of 74 and 120 degrees were manufactured by DSF method, which was recently proposed by the authors. Of course, most of design parameters were chosen by the aid of simulation results. Finally, the results of average luminance values were compared between the simulation and DSF molded samples.

• 한국결정성장학회지
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• 제17권5호
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• pp.210-216
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• 2007

극청정 가스필터용 다공성 멤브레인을 제조하기 위해 금속산화물 분말의 in-situ한 환원/소결 공정을 이용하였다. 또한 기공도의 향상을 위해 solid pore forming agent로써 구형의 폴리머 입자를 첨가하여 금속 섬유를 사용한 멤브레인과 비슷한 52%의 기공도를 가지는 니켈 멤브레인을 제조하였다. 제조된 니켈 멤브레인은 폴리머의 첨가에 따라 평균기공크기와 기공도가 증가하였다. 한편 환원/소결 온도가 $800^{\circ}C$에서 $1000^{\circ}C$로 상승함에 따라 평균기공크기와 기공도는 감소하였다. 이는 환원/소결 온도가 상승함에 따라 격자확산 및 입계확산이 진행되어 멤브레인의 수축률 증가를 일으켰기 때문이다.

• 대한치과의사협회지
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• 제57권12호
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• pp.747-756
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• 2019

This paper reviews the adaptation accuracy and mechanical properties of currently used denture processing systems with base resin materials and introduces the latest research on the development of antimicrobial denture base resins. Poly(methyl methacrylate) has been successfully used as a dental denture base resin material by the compress-molding method and heat polymerization for a long time, but recently, new processing techniques, injection molding-methods or fluid-resin technique are also used for fabricating denture base. However, studies indicated that there was no difference between the injectionmolding and the conventional compression-molding method in terms of adaption accuracy of denture base. The fluid-resin fabrication and one injection-molding systems exhibited better adaptation accuracy than the other processing methods. Resin denture bases in the oral cavity may undergo midline fractures due to flexural fatigue from repeated masticatory loading. For those patients, impact resistant denture base resins are recommended to prevent denture fracture during service. Thermoplastic denture base resins can be helpful for patients suffering from allergic reaction to resin monomers with a soft-fit, however, thermoplastic resins with low stiffness can irritate gum tissues and accelerate abnormal alveolar ridge resorption. Moreover, due to low chemical durability in oral cavity, those should be used for a limited period of time.

• 한국전기전자재료학회논문지
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• 제30권1호
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• pp.48-53
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• 2017

We report the studies on the red organic phosphor by using perylene bisimide derivatives. Even though perylene bisimide derivatives have excellent thermal stability and luminous efficiency, they have low solubility in organic solvents. In this research, modified perylene bisimide derivative, N,N'-Bis(4-bromo-2, 6-diisopropylphenyl)-1, 6, 7, 12-tetraphenoxyperylene-3, 4, 9, 10-tetracarboxyl bisimide (1C), has been prepared by the reaction of phenol with N,N'-Bis(4-bromo-2, 6-diisopropylphenyl)-1, 6, 7, 12-tetrachloroperylene-3, 4, 9, 10-tetracarboxyl bisimide (1B) in presence of DMF, at $70^{\circ}C$. The synthesized (1C) was characterized by using $^1H-NMR$, FT-IR, UV/V is spectroscopy, and TGA. The absorbtion and emission of (1C) was shown at 576 nm and 610 nm in UV/V is spectrum. In TGA thermogram, (1C) showed good thermal stability without significant weight loss to $220^{\circ}C$. And in the solubility analysis, (1C) with phenoxy group showed the good solubility in general organic solvents. The blended films of (1C) with PMMA (polymethyl methacrylate) at different weight % concentration such as 10, 5, 1 weight % have been prepared. The blended film was shown at 616 nm when monitored at 450 nm in PL emission spectra.

• Biomaterials and Biomechanics in Bioengineering
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• 제1권2호
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• pp.95-104
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• 2014

The objective of this study was to evaluate the cytotoxicity of poly (lactic acid) (PLA) nanoparticles. We used a water-soluble, amphiphilic phospholipid polymer, poly (2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) (PMB30W), as a stabilizer for the PLA nanoparticles. The PLA nanoparticles and PMB30W-modified PLA (PLA/PMB30W) nanoparticles were prepared by evaporating tetrahydrofuran (THF) from its aqueous solution. Precipitation of the polymers from the aqueous solution produced PLA and PLA/PMB30W nanoparticles with a size distribution of $0.4-0.5{\mu}m$. The partial coverage of PMB30W on the surface of the PLA/PMB30W nanoparticles was confirmed by X-ray photoelectron spectroscopy (XPS) and dynamic light-scattering (DLS). A high-content automated screening assay (240 random fields per group) revealed that the PLA nanoparticles induced apoptosis in a mouse macrophage-like cell line (apoptotic population: 73.9% in 0.8 mg PLA/mL), while the PLA/PMB30W nanoparticles remained relatively non-hazardous in vitro (apoptotic population: 13.8% in 0.8 mg PLA/mL). The reduction of the apoptotic population was attributed to the phosphorylcholine groups in the PMB30W bound to the surface of the nanoparticle. In conclusion, precipitation of PLA in THF aqueous solution enabled the preparation of PLA nanoparticles with similar shapes and size distribution but different surface characteristics. PMB30W was an effective stabilizer and surface modifier, which reduced the cytotoxicity of PLA nanoparticles by enabling their avoidance of the mononuclear phagocyte system.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.218.2-218.2
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• 2014

그래핀은 높은 전기 전도도와 열전도도, 기계적 강도를 가지고 있고 동시에 높은 전자이동도($200,000cm^2{\cdot}V{\cdot}^1{\cdot}s{\cdot}^1$) 특성을 갖는 물질로써 차세대 소재로 각광받고 있다. 하지만 그래핀을 소자에 응용하기 위해서는 전사공정과 lithography 공정 과정에서 발생되는 PMMA(Poly methyl methacrylate) residue를 완벽하게 제거해야 하는 문제점이 있다. 특히, lithography 공정 중 완벽하게 PMMA residue 가 제거되지 않고 잔류해 있을 경우에 소자의 life time, performance에 악영향을 준다는 보고가 있다. 이와같은 문제를 해결하기 위해 화학적 cleaning, 열처리를 통한 cleaning, 전류 인가에 의한 cleaning과 같은 방법들을 이용하여 그래핀의 PMMA residue를 제거하는 공정들이 보고되고 있지만, 화학적 cleaning 방법의 경우 chloroform 이라는 독성물질 사용으로 인해 산업적으로 응용이 어렵고, 열처리 방법은 전극 등의 금속이 $200^{\circ}C$ 이상의 높은 온도에서 장시간 노출될 경우 쉽게 손상을 입으며, 전류 인가에 의한 cleaning 방법은 국부적으로만 효과를 볼 수 있기 때문에 lithography 공정 후 PMMA residue를 효과적으로 제거하기에는 한계를 보이고 있다. 본 연구에서는 Ar을 이용하는 Ion beam 시스템을 통해 beam energy를 제어함으로써 PMMA residue를 효과적으로 제거하는 연구를 진행하였다. 최적화된 플라즈마 발생 조건을 찾기 위해 QMS(Quadrupole Mass Spectrometer)를 이용하여 입사하는 ion energy와 flux 양을 컨트롤 하였고, 250 W에서 최적화된 ion energy distribution 영역이 존재한다는 것을 확인할 수 있었다. 또한, 25 Gauss 정도의 electro-magnetic field를 이용하여 Ar의 ion energy를 10 eV 이하로 낮추어 damage를 최소화함으로써 효과적으로 그래핀을 cleaning 할 수 있었다. Cleaning과정에서 ion bombardment에 의해 발생한 damage는 $250^{\circ}C$에서 6시간 동안 annealing 공정을 거치면서 회복되는 것을 Raman spectroscopy의 D peak ($1335cm{\cdot}^1$) / G peak ($1572cm{\cdot}^1$) ratio 로 확인할 수 있었고, PMMA residue의 cleaning 여부는 G peak ($1580cm{\cdot}^1$)의 blue shift와 2D peak ($2670cm{\cdot}^1$)의 red shift를 통해 확인하였다. 그리고 AFM (Atomic Force Microscopy)을 이용하여 cleaning 공정과정에서 RMS roughness가 4.99 nm에서 2.01 nm로 감소하는 것을 관찰하였다. 마지막으로, PMMA residue의 cleaning 정도를 정량적으로 분석하기 위해 XPS (X-ray Photoelectron Spectroscopy)를 이용하여 sp2 C-C bonding이 74.96%에서 87.66%로 증가함을 확인을 할 수 있었다.