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양승화,신현성,조맹효 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.1
The mechanical behavior of oxygen functionalized single layer graphene (graphene oxide, GO)/polyethylene (PE) nanocomposites is studied by all atom-based molecular dynamics (MD) simulation and finite element analysis (FEA). To account for the effect of the oxygen functional group, both pristine and 15 hydroxyl functionalized graphene embedded into the transversely isotropic nanocomposites unit cell models are considered. Using the classical ensemble simulations at 200K and at atmospheric pressure, the transversely isotropic elastic constants of the nanocomposites molecular unit cell structures are determined from uniaxial tension and shear tests. To evaluate the effect of the addressed oxygen functional groups on elastic constants of the nanocomposites, periodic FEA models with the perfect interface condition between the graphene and PP matrix are constructed. Due to the degradation of the graphene by the oxidation, the longitudinal Young’s modulus and the in-plane shear modulus of the nanocomposites determined from the MD simulation and FEA are found to be degraded by the oxygen functional groups. According to the MD simulation results, however, the longitudinal shear modulus of the nanocomposites is improved by the oxygen functional groups compared with the pristine graphene. On the other hand, FEA analysis of the longitudinal shear modulus is overestimated unless the oxygen functional group-dependent cohesive interface law between the graphene and PP matrix is addressed.
양승화,윤수진,권선영 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.5
While poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane, pV3D3) is a promising dielectric material, synthesized from an iCVD process, the physical properties of pV3D3 film have yet to be studied in detail. In this study, the thermoelastic properties of pV3D3 are investigated by molecular dynamics simulations. An amorphous molecular unit cell of pV3D3 is modeled with periodic boundary conditions. The PCFF force field is applied to describe all the inter- and intramolecular interactions. Through classical ensemble simulations, the mechanical properties including the stress-strain curves in tension and compression are determined. The glass transition temperature and the coefficient of thermal expansion are determined from the simulation of cooling-down from an elevated temperature. The simulation results show that the pV3D3 is in an almost rubbery state near room temperature. Moreover, a clear hydrostatic pressure effect is observed in the compressive loading condition of pV3D3 and its elastic modulus is within the range of typical thermoplastic.
나노입자의 크기효과와 체적분율 효과를 동시 고려한 나노복합재의 멀티스케일 브리징 해석기법에 관한 연구
양승화,유수영,조맹효,Yang, Seung-Hwa,Yu, Su-Young,Cho, Maeng-Hyo 한국전산구조공학회 2009 한국전산구조공학회논문집 Vol.22 No.4
본 연구에서는 분자동역학 전산모사와 미시역학 모델을 이용하여 나노입자의 체적분율이 높은 경우 나노 입자의 크기효과와 체적분율 효과가 나노복합재의 기계적 물성에 미치는 영향을 효과적으로 묘사할 수 있는 순차적 브리징 해석기법을 제안하였다. 체적분율이 12%로 고정된 상태에서 나노입자의 크기변화에 따른 영률과 전단계수를 분자동역학 전산모사를 통해 예측한 후, 이를 연속체 모델에서 구현하기 위해 다중입자모델을 적용하였다. 나노입자의 크기효과를 반영하기 위해 입자와 기지 사이에 유효계면을 추가적인 상으로 도입하였고, 12%의 체적분율 조건에서 나타날 수 있는 체적분율 효과는 나노복합재를 둘러싸는 가상의 영역인 무한영역의 물성값의 변화를 통해 조절되도록 하였다. 유효계면과 무한영역의 물성을 입자의 반경에 대한 함수로 근사한 후 다양한 입자의 크기에서 나타나는 나노복합재의 물성변화의 예측이 가능하도록 하였다. 제안된 브리징 해석기법의 적용을 통해 분자동역학 해석결과와 잘 일치하는 결과를 연속체 모델에서 효율적이고 정확하게 얻을 수 있었다. 또한 유효계면의 두께와 물성 변화가 나노복합재의 기계적 물성에 미치는 영향을 고찰하였다. In this study, an efficient sequential bridging method to characterize both the particle size effect and concentration effect on the mechanical properties of nanocomposites at high volume fraction is suggested through a molecular dynamics(MD) simulations and micromechanics of composites materials. The Young's modulus and the shear modulus of the nanocomposites at various particle radius and at 12% volume fraction were obtained from MD simulations and multi-inclusion model was adopted to describe both modulus in continuum model. In order to describe the particle size effect, an additional phase, effective interface, was adopted as characteristic phase and the non-dilute concentration effect which appears at 12% volume fraction was describe via the variation of the elastic modulus of the infinite medium. Both the elastic modulus of the interface and infinite medium were fitted into functions of particle radius for the applicability of the present bridging method at various particle radii. Using the present bridging method the elastic modulus of the nanocomposites was efficiently obtained with accuracy. In addition, the effect of the interface thickness and modulus on the elastic modulus of the nanocomposite was investigated.
계면 결합력과 나노튜브의 응집에 따른 나노튜브/고분자 복합재의 탄소성 거동 예측에 대한 연구
양승화,유수영,류정현,조맹효,Yang, Seunghwa,Yu, Suyoung,Ryu, Junghyun,Cho, Maenghyo 한국전산구조공학회 2013 한국전산구조공학회논문집 Vol.26 No.6
본 연구에서는 탄소나노튜브와 폴리프로필렌 기지 간 계면결합력과 나노튜브의 국부적 응집에 따른 나노복합재의 탄소성 거동 변화에 대한 파라메트릭 연구를 수행한다. 나노복합재의 탄소성 거동 예측을 위해 분자동역학 전산모사를 수행하고, 분자동역학 결과와 Mori-Tanaka 모델을 적용한 비선형 미시역학 모델을 연계하여 나노복합재 내 흡착계면의 탄소성 거동을 역으로 도출하는 2단계 영역분할 기법을 적용하였다. 미시역학 모델에서는 시컨트 계수방법을 Mori-Tanaka 모델에 적용하여 나노복합재의 비선형 거동을 예측하는 방법을 적용하였으며, 나노튜브와 기지 간 재료계면의 불완전 결합을 고려하기 위해 변위 불연속 조건을 적용하였다. 흡착영역을 고려한 미시역학 모델을 통해 흡착계면의 유무 및 재료계면 결합력 변화 그리고 나노튜브의 국부적 응집현상에 따른 나노복합재의 응력-변형률 관계를 예측하였다. 그 결과 나노튜브의 국부적 응집이 나노복합재의 강화효과를 저하시키는 가장 중요한 변수임을 확인하였다. In this research, a paramteric study to account for the effect of interfacial strength and nanotube agglomeration on the elastoplastic behavior of carbon nanotube reinforced polypropylene composites is performed. At first, the elastoplastic behavior of nanocomposites is predicted from molecular dynamics(MD) simulations. By combining the MD simulation results with the nonlinear micromechanics model based on the Mori-Tanaka model, a two-step domain decomposition method is applied to inversely identify the elastoplastic behavior of adsorption interphase zone inside nanocomposites. In nonlinear micromechanics model, the secant moduli method combined with field fluctuation method is used to predict the elastoplastic behavior of nanocomposites. To account for the imperfect material interface between nanotube and matrix polymer, displacement discontinuity condition is applied to the micromechanics model. Using the elastoplastic behavior of the adsorption interphase zone obtained from the present study, stress-strain relation of nanocomposites at various interfacial bonding condition and local nanotube agglomeration is predicted from nonlinear micromechanics model with and without the adsorption interphase zone. As a result, it has been found that local nanotube agglomeration is the most important design factor to maximize reinforcing effect of nanotube in elastic and plastic behavior.
Camellia japonica 덖음 잎 추출물의 항산화 활성 및 피부질환 유발균 저해 효과
양승화,이여진,신현재,오득실,최문희 한국생물공학회 2022 KSBB Journal Vol.37 No.4
Natural products have been used in various ways for the promotion of health and the treatment of diseases since ancient times. In particular, polyphenolic compounds contained in natural products offer various physiological activities such as antioxidant, cancer cell growth inhibition, and antimutation, and many studies are being conducted to examine the possibility of using them as therapeutic and preventive agents for cardiovascular diseases and cancer. Camellia japonica has been studied on various physiological activities of leaves, flowers, and seed extracts. However, there has been little research on the antibacterial activity of C. japonica extract, and the effect on antibacterial activity is different depending on the heat-treated process. Therefore, in this study, extracts of heat-treated C. japonica leaves were prepared using hot water, 70% EtOH, and 100% EtOH solvents, and each extract was compared through antioxidant activities (DPPH and ABTS), total polyphenol contents (TPC), and total flavonoid contents (TFC). The 70% EtOH extract showed the best activity, and DPPH and ABTS radical scavenging IC 50 were 262.99 µg/mL and 319.97 µg/mL. TPC also showed the highest content at 167.88 GAE mg/g. However, TFC confirmed that the contents of each extract were similar. As a result of HPLC analysis, it was confirmed that polyphenols and vitamins showed the highest content in the 70% EtOH extract, and it is thought that there is a need for additional research through more subdivided separation and fractionation. As a result of the disk diffusion test, the activities of Staphylococcus epidermidis and Malasseiza pachydermaits were the best in the 70% EtOH extract. C. Japonica leaves are thought to be very suitable as a functional cosmetic raw material.