• Structural Engineering and Mechanics
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• 제71권3호
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• pp.283-290
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• 2019

In global competition manufacturing companies have to produce modern, new constructions from advanced materials in order to increase competitiveness. The aim of my research was to develop a new composite cellular plate structure, which can be primarily used for structural elements of road, rail, water and air transport vehicles (e.g. vehicle bodies, ship floors). The new structure is novel and innovative, because all materials of the components of the newly developed structure are composites (laminated Carbon Fiber Reinforced Plastic (CFRP) deck plates with pultruded Glass Fiber Reinforced Plastic (GFRP) stiffeners), furthermore combines the characteristics of sandwich and cellular plate structures. The material of the structure is much more advantageous than traditional steel materials, due mainly to its low density, resulting in weight savings, causing lower fuel consumption and less environmental damage. In the study the optimal construction of a given geometry of a structural element of a road truck trailer body was defined by single- and multi-objective optimization (minimal cost and weight). During the single-objective optimization the Flexible Tolerance Optimization method, while during the multi-objective optimization the Particle Swarm Optimization method were used. Seven design constraints were considered: maximum deflection of the structure, buckling of the composite plates, buckling of the stiffeners, stress in the composite plates, stress in the stiffeners, eigenfrequency of the structure, size constraint for design variables. It was confirmed that the developed structure can be used principally as structural elements of transport vehicles and unit load devices (containers) and can be applied also in building construction.

• 반도체디스플레이기술학회지
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• 제16권4호
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• pp.41-45
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• 2017

We have investigated the light extraction efficiency of large-area OLED lighting panels with a microlens array (MLA) or external scattering layer (ESL) by ray tracing simulation. The application of MLA and ESL to transparent OLEDs (TOLEDs) with an auxiliary metal electrode is also studied. It is found that MLA shows higher light extraction efficiency, compared with ESL. However, we have demonstrated that ESL is more suitable for TOLEDs having dual-sided equal light emission. Namely, equal light emission from the front and rear surfaces of TOLED can be achieved by increasing the scattering particle density of ESL. To compensate for a loss in light emission induced by auxiliary metal electrode, we come out with an OLED structure partially covered with MLA at the outer surface of glass substrate, which is aligned with metal electrode. With this scheme, it is observed that the light extraction efficiency can be boosted more than 20% from opaque OLED and 50% from transparent OLED.

• 한국융합학회논문지
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• 제9권12호
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• pp.99-106
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• 2018

의료방사선 방어를 위해 사용되는 차폐 시트의 제조과정에서 인장강도를 유지하면서 차폐 재료의 충전율을 높여 차폐 성능을 향상시키는 방안을 제시하고자 한다. 본 연구에서 제안된 개질제는 고분자 수지재료와의 융합에 있어서 분자량을 높여 재료의 친화성을 높이는 역할을 수행한다. 차폐시트의 산화텅스텐의 충전율과 인장강도, 차폐 성능 등을 평가하였다. 공정과정에서 개질제는 분자량과 밀도를 증가시켰고, 성형 과정에서 퍼짐 형상이 적용되었고, 성능 향상과 재료와의 친화성, 인장강도를 유지하기 위해 사용된 개질제 PMMA는 20%를 혼합할 경우 가장 우수한 효과를 얻을 수 있다. 본 연구에서 제시된 재료의 융합과 개질제를 통해 차폐시트의 대량생산이 가능하며, 향후 경량의 차폐복 제작에 기여할 것입니다.

• Elastomers and Composites
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• 제57권1호
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• pp.13-19
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• 2022

Polycarbonate diol-based waterborne polyurethane (WPU) was prepared by prepolymer mixing process. The prepolymer mixture contained the polycarbonate diol, isophorone diisocyanate (IPDI), dimethylol propionic acid, triethylamine, and ethylenediamine (EDA). The NCO/OH ratio in the prepolymer was adjusted by controlling the molar ratio of IPDI, and its effects on the properties of WPU were studied. The structure of WPU was characterized by fourier transform infrared spectroscopy. The average particle size increased and viscosity decreased with increasing NCO/OH ratio and EDA content in WPU. The reduced phase separation between soft and hard segments increased glass transition temperature. The reduction in the thermal decomposition temperature could be attributed to the low bond energy of urethane and urea groups, which constituted the hard segment. Additionally, the polyurethane chain mobility was restricted, elongation decreased, and tensile strength increased. The hydrogen bond between the hard segments formed a dense structure that hindered water absorption.

• Elastomers and Composites
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• 제57권3호
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• pp.100-106
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• 2022

Waterborne polyurethane-acrylate(WPUA) dispersions were prepared by surfactant-free emulsion polymerization in a two-step process. In the first step, polytetrahydrofuran, isophorone diisocyanate, dimethylol proponic acid, and 2-hydroxyethyl methacrylate were used to synthesize a vinyl-terminated polyurethane prepolymer. In the second step, styrene, methyl methacrylate, butyl acrylate, and different multi-functional crosslinkers were copolymerized. 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, and pentaerythritol tetraacrylate were used as the crosslinkers, and their effect on the mechanical and thermal properties of WPUA was investigated. Overall, as the number of functional groups of the cross-linker increased, the gel fraction improved to 79.26%, the particle size increased from 75.9 nm to 148.7 nm, and the tensile strength was improved from 5.86 MPa to 12.40 MPa. In thermal properties, the glass transition temperature and decomposition temperature increased by 9.9℃ and 18℃, respectively. The chemical structures of the WPUA dispersions were characterized by Fourier-transform infrared spectroscopy. The synthesized WPUA has high potential for applications such as coatings, leather coatings, adhesives, and wood finishing.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 춘계학술발표강연 및 논문개요집
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• pp.44-44
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• 2003

Growth mechanism of carbon nanotubes(CNTs) synthesized by chemical vapor deposition is abided by two growth modes. These growth modes are classified by the position of activated catalytic metal particle in the CNTs. Growth mode can be also affected by interaction between substrate and catalytic metal and induced energy such as thermal and plasma. We studied the reaction of catalytic metal to the substrate and growth mode of CNTs. Various substrates such as Si(100), graphite plate, coming glass, sapphire and AAO membrane are used to study the relation between catalytic metal and substrate in the synthesis of CNTs. For catalytic metal, thin film was deposited on various substrate via sputtering technique with a thickness of ∼20nm and magnetic fluids with none-sized particles were dispersed on AAO membrane. After laying process on AAO membrane, it was dried at 80$^{\circ}C$ for 8 hour. Synthesizing of CNTs was carried out at 900$^{\circ}C$ in NH3/C2H2 mixture gases flow for 10minutes.

• 환경위생공학
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• 제9권1호
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• pp.53-61
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• 1994

Sungnam city, as a major satellite town, is located in the southeast of Seoul. Atmospheric conditions are so stable that air pollutants from various emissions are tend to resist change because Sungnam city is located in the Namhansansung valley. The industrial distribution of Sungnam city are composed of various manufactories such as foods, fibers, chemicals, machinery and electronics etc. The heavy metal concentrations and size distribution are the most important parameters influencing among the way in which respirable suspended particulate matter interact with the human respiratory system. Respirable suspended particulate matter was collected on glass fiber filters from April 1993 to February 1994 according to particle size using Anderson sampler during 10 days per month at Sungnam city. 6 heavy metals, Fe, Zn, Pb Mn, Cu and Cd, were analyzed by particle size with atomic absorption spectrophotometry . The results could be summarized as follows: 1. The annual arithmetic mean concentration of total suspended particulate was 116.3$\mu $g/m$^{3}$ m', seasonal variation was the highest in spring season(196.5$\mu $g/m$^{3}$) and the lowest in Summer Season(72.9$\mu $g/m$^{3}$). 2. The ratio of airborne particulate concentrations respirable to nonrepairable( Res/Non- Res) of annual arithmetic mean value was 5.8'1, seasonal variation was highest in the spring season(6.3 : 1) and lowest in the summer season(4.6 : 1). 3. During the spring season the shape of the size distribution was trimodal which showed peaks at 3 size groups, which were below of 0.43$\mu $m, 3.3∼4.7$\mu $m and above of 11.0$\mu $g/m$^{3}$ respectively. 4. Respirable suspended particulate matter concentrations of Zn, Pb Cu and Cd were the highest in below of 0.43$\mu $m as follows; 0.517$\mu $g/m$^{3}$, 0.411 $\mu $g/m$^{3}$, 0.062$\mu $g/m$^{3}$ and 0.0310$\mu $g/m$^{3}$ , respectively, Fe and Mn were the highest in the particle size range of 4.7 ∼ 7.0$\mu $m as follows; 2.504$\mu $g/m$^{3}$ and 0.095$\mu $g/m$^{3}$, respectively. 5. The Pt Cd, Zn, Cu, Fe and Mn concentrations of annual arithmetic mean value respirable to non- respirable( Res/Non- Res ) were 33.65, 19.27, 17.74, 10.54, 3.20 and 5.20, respectively.

• 청정기술
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• 제11권1호
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• pp.41-50
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• 2005

본 연구는 환경친화적인 선형 비이온 계면활성제인 LE-형유화제를 사용하여 점착성분의 단량체로 노말부틸 아크릴레이트 (n-butyl acrylate, n-BA)와 응집성분의 단량체로 메틸메타 아크릴레이트 (methyl metacrylate, MMA)를 사용하여, 폴리머 시멘트용 아크릴계 에멀젼 수지를 제조하기 한 최적조건을 얻기 위해 수용액상에서 유화중합을 실시하였다. 실험결과, 사용한 계면활성제 (LE-형)의 친수성인 체인 길이(n)의 값이 증가할수록 응석의 발생이 줄어들어 안정한 폴리머 에멀젼을 얻을 수 있었다. 최종 폴리머 에멀젼의 농도는 이 계면활성제의 사용량을 증가시킴에 따라 증가하다가 어느 농도 이상에서 응석의 발생이 거의 없는 폴리머 에멀젼을 얻을 수 있었으며, 반면에 평균 입자크기도 사용량에 따라 작아지다가 250 nm로 일정한 크기를 나타내었다. 또한 기능성 폴리머로서 보조모노머의 첨가는 최종 폴리머 에멀젼의 응석과 입자크기에 크게 영향을 미쳤는데, 주 모노머에 보조 모노머인 아크릴산 (acrylic acid, AA)과 아크릴 아마이드 (acrylic amide, AM)의 혼합하여 첨가한 경우, 첨가하지 않은 경우에 비해 응석의 발생이 줄어들어 안정한 폴리머 에멀젼을 얻을 수 있었다. 최적조건에서 어진 아크릴 폴리머 에멀젼은 평균 입자크기 200-300 nm, 제타전위 (zeta potential)값 -50 mv 정도였으며, 단일 유리전이온도 (glass temperature, Tg)를 가진 고분자 나노 입자가 수용액상에 잘 분산되어 있음을 알 수 있었다. 따라서 중합조건을 최적화시켜 안정된 폴리머 에멀젼을 얻을 있었다.

• Elastomers and Composites
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• 제47권1호
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• pp.43-53
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• 2012

물을 반응매체로 하고 스티렌과 부틸메타크릴레이트 (BMA)를 단량체로 하여 $65^{\circ}C$에서 $95^{\circ}C$ 사이의 선택된 온도에서 현탁중합을 실시하였다. 소수성 실리카를 안정제로, azobisisobutyronirile (AIBN)을 개시제로 선택하였다. 안정제의 최적 분산은 pH 10에서 이루어졌으며 반응은 pH 7에서 진행하였다. TGA 및 EDS 측정으로 사용한 실리카의 90%는 안정제로 10%는 입자 내로 유입되는 것으로 분석되었다. 안정제의 농도가 증가할수록 평균입경은 감소하였다. 분자량은 안정제의 농도가 1.67 wt%에 이르며 증가하였다. 개시제의 농도 및/혹은 반응온도의 상승에 따라 반응속도는 증가하였으나 분자량은 감소하였다. 입자의 입경은 개시제의 농도 및 반응온도에 거의 무관하였다. BMA의 비가 증가하면서 유리전이온도는 감소하였으며 불규칙한 형상의 입자가 증가하였다. 카본블랙을 함유하는 스티렌/BMA의 중합반응은 반응완료에 보다 많은 시간이 소요되었다. 소수성 실리카를 안정제로 하는 현탁중합반응을 이용하여 카본블랙을 함유하는 평균입경이 $1-30{\mu}m$의 구형 폴리(스티렌-BMA) 공중합체 복합체 입자를 합성할 수 있다는 사실을 확인하였다.

• 분석과학
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• 제23권2호
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• pp.216-223
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• 2010

Ag 분말 입자형태와 크기에 따른 효율성을 확인한 결과 flake, spherical 형태의 분말은 시판 회색 분말과 현출효율이 유사하였고, nAg (rod, $0.9\;{\mu}m$) 분말의 경우 다양한 잠재지문 현출효율 평가 실험에서 우수한 결과를 보였다. 그러나 1개월간 nAg 분말을 자연조건에서 방치하였을 때 분말의 산화 및 수분의 영향으로 현출효율이 낮게 확인되어 산화 및 수분 흡습 방지를 위한 연구가 제기되었다. 본 연구는 nAg 분말의 산화 및 수분 흡습의 단점을 보완하기위해 nAg 분말에 실리콘 오일을 다양한 수준으로 표면개질하여 비다공성 대상물질 표면인 유리, 플라스틱에서 현출지문의 동일한 영역에서 특징점 수, 이랑과 분말의 흡착정도, 현출지문의 contrast 등으로 nAg 분말과 표면개질 nAg 분말의 현출효율을 평가하여 유리, 플라스틱 대상물질에서 DC200 실리콘 오일 0.5%로 표면개질한 nAg 분말의 우수함과 산화 및 수분 흡습의 단점을 보완할 수 있었다.