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Kim, Daeyeon,Lee, Dong Geun,Kim, Jin Chul,Lim, Choong Sun,Kong, Nam Sik,Kim, Jin Hong,Jung, Hyun Wook,Noh, Seung Man,Park, Young Il Butterworth-Heinemann Ltd. 2017 International journal of adhesion & adhesives Vol.74 No.-
<P><B>Abstract</B></P> <P>Rheological and adhesive properties of automotive structural adhesives including polyurethane (PU) toughening agents have been investigated by adjusting the molar ratio of polytetrahydrofuran (polyTHF) and hexamethylene diisocyanate (HMDI) for the control of molecular weight of a PU prepolymer. Thixotropic behavior, crosslinking characteristics, and lap-shear and T-peel adhesion strengths for various adhesives were significantly affected by single or binary-mixed PUs with different molecular weights. Thixotropic hysteresis loop of shear viscosity along with shear rate of an adhesive became larger with increasing PU molecular weight, exhibiting favorable flowability, however, the adhesion strengths were not satisfactory for injection and coating applications. We found that both rheological and adhesive properties of adhesives could be interestingly tuned by combining PU components with different molecular weights.</P>
PLASMA EFFECTS ON HUMAN LIVER CANCER CELLS
Daeyeon Kim,Bomi Gweon,Danbee Kim,Sukhyun Song,Mina Kim,Se Youn Moon,Wonho Choe,Jennifer H. Shin 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Low pressure plasma has been widely used in surface treatment of solid materials. In recent years, atmospheric plasma (cold plasma) is introduced in biomedical applications. In general, many types of cellular behaviors depend on the plasma density or intensity. While the plasma-treated cells are detached because of the plasma-induced damage of cell adhesion molecules at low plasma density, the cell membranes are destructed and the necrosis of cells occurs at high plasma density. In this research, we investigate the effects of plasma on cancerous cells. We treat the target human liver cancer cells (HepG2 and SK-Hep1) using a He plasma needle device, which has a pin type plasma jet. We aim to identify the plasma effects on cancerous cells as a function of the treatment time and applied power. This study may contribute to the development of a novel cancer therapy.
에폭시 수지/방향족 아민 경화물의 배합비 변화에 따른 열적 특성 분석
김대연 ( Daeyeon Kim ),김순천 ( Soonc Hoen Kim ),박영일 ( Young Il Park ),김영철 ( Young Chul Kim ),임충선 ( Choong Sun Lim ) 한국접착및계면학회 2014 접착 및 계면 Vol.15 No.3
본 연구에서는 비스페놀 A 에폭시 수지/경화제(YD-128/DDM) 조성물의 비율을 조절하여 170°C의 경화온도에서 접착성능 최적화 조성비를 얻기 위한 실험을 진행하였다. DSC, TGA, DMA, TMA 열분석 장비를 사용하여 YD-128/DDM 혼합물의 당량비 변화가 경화물의 열적 특성에 미치는 영향에 대하여 조사하였으며, 조성물의 경화시간은 YD-128/DDM (1 : 1.1) 조성물을 동적 DSC를 이용하여 측정된 시간당 누적 발열량을 총 발열량으로 나누어 계산한 전환율을 토대로 결정하였다. TGA를 이용한 분해 활성화 에너지 분석에서는 경화물의 DDM 당량비가 증가할수록 열안정성과 열분해 활성화 에너지가 높게 나타났고, DMA와 TMA를 이용한 경화물의 열적 특성 조사 결과에서는 당량비 1 : 1에서 다른 당량비 조건에 비해 우수한 탄성률 및 열팽창성이 관찰되었다. 또한 각기 다른 당량비의 조성물을 170°C에서 경화하여 중첩 전단 강도를 측정하였다. In this work, a series of molar ratios composed with YD-128 and DDM were chosen based on the viscosity analysis. The mixtures of YD-128 and DDM with the different molar ratios were cured at 170°C for 15 min followed by post cure at 190°C for two hours. The thermal properties of the cured samples were investigated with DSC, TGA, DMA, and TMA. The conversion ratio of the mixtures of YD-128 and DDM (1 : 1.1) was calculated by dividing ΔH obtained from DSC experiments for each cured sample by ΔH. The TGA data of the cured samples showed that the thermal stability and thermal degradation activation energy were proportional to the amount of DDM in the mixtures. However, the highest tan δ, and the lowest thermal expansion data with DMA and TMA respectively were obtained from the stoichiometric mixture of YD 128 and DDM. Furthermore, the different ratio of mixtures were applied to test specimens to be cured at 170 C to measure single lap shear strength with universal testing machine.
김대연 ( Daeyeon Kim ),김순천 ( Soonchoen Kim ),박영일 ( Young Il Park ),김영철 ( Young Chul Kim ),임충선 ( Choong Sun Lim ) 한국접착및계면학회 2015 접착 및 계면 Vol.16 No.3
코어/쉘 나노입자, CTBN 변성에폭시, 폴리에스터 폴리올, 폴리우레탄 등과 같은 다양한 종류의 강인화 소재는 에폭시 수지의 주요 단점으로 알려진 취성을 보완하여 낮은 충격 저항성을 개선시키기 위한 방법으로 연구되고 있다. 본 연구에서는 앞서 언급된 강인화 소재를 선정, 접착제 조성물에 첨가하여 기계적 물성을 조사하였다. 강인화 소재 도입에 따른 기계적 강도의 측정은 UTM을 이용한 굴곡 강도와 탄성률 측정 및 Izod 충격 시험기를 사용한 충격 강도 실험을 통해 이루어 졌으며, 그 결과 강인화 소재가 에폭시 경화물의 유연성 및 충격에 대한 저항성 향상에 미치는 긍정적인 효과가 나타남을 관찰하였다. 또한, DMA를 이용한 저장 탄성률 결과는 굴곡 탄성률의 결과와 동일한 경향으로 나타남을 확인하였다. 강인화 소재가 충격 강도 향상에 영향을 주는 이유는 에폭시 수지에 첨가된 강인화 소재의 상 분리 현상에 의한 것이며, 상 분리된 강인화 소재는 에폭시 조성물의 파단면을 관찰한 FE-SEM 이미지에서 관찰하였다. Epoxy resin toughening agents such as core/shell nanoparticles, CTBN epoxy, polyester polyols, and polyurethane have been widely used in order to compensate for the brittleness and improve the impact resistance of the epoxy resin. In this work, a few tougheners mentioned above were individually added into adhesive compositions to observe the effects of physical and mechanical properties. Both flexural strength and flexural modulus were measured with UTM while impact strength was analyzed with Izod impact tester. The obtained results showed that the addition of toughening agents afforded positive performance in terms of flexibility and impact resistance of the cured epoxy resin. Furthermore, DMA experiments suggested that the trends of storage modulus data of each epoxy resin composition coincided with the trends of flexural modulus data. FE-SEM images showed that toughening agents formed circled-shape particles when it was cured in epoxy resin composition at high temperature by phase separation. The existence of particles in the cured samples explains why epoxy resin with toughener has higher impact resistance.
Turning mechanism of a smooth body by amplitude and period control in curvature
Daeyeon Kim,Hyejin Hwang,Sungsu Park,Jennifer H. Shin 제어로봇시스템학회 2008 제어로봇시스템학회 국제학술대회 논문집 Vol.2008 No.10
C. elegans’crawling locomotion including simple running and turning is analyzed with a mathematical model. C. elegans moves forward and backward by propagating dorso-ventral contraction waves toward the opposite direction of its movement. For straight run, the worm maintains a constant amplitude and period in its body curvature. While it changes these quantities during smooth turn. Two types of smooth turn are described theoretically based on the experimental observation. One has the turning strategy to increase both of amplitude and period of the curvature. The other is characterized by decrement of these parameters. Our results may contribute to understanding the lateral undulation of other smooth body animals like snakes and these could further be applied to the developments of bio-inspired robots.