Influences of the molecular structures of curing agents on the inelastic-deformation mechanisms in highly-crosslinked epoxy polymers

Park, Hyungbum,Kim, Byungjo,Choi, Joonmyung,Cho, Maenghyo Elsevier 2018 Polymer Vol.136 No.-

<P><B>Abstract</B></P> <P>The nature of the inelastic-deformation characteristics of highly-crosslinked epoxy polymers has been understood at the microscopic level and in consideration of the structural network-topology differences. The structural differences that arise from different types of curing agents (aliphatic and aromatic) have been estimated using the compressive loading–unloading responses in terms of the energy, stress, and geometric characteristics. The energy and stress distributions at 300 K revealed that the nonbonded interactions of the polymer chains and the local dihedral-angle behaviors are key internal-potential components that accommodate the applied levels of the deformation energy and stress. In particular, a residual dihedral-angle stress was observed in the monomers of aromatic curing agents after the unloading, while the aliphatic-cured system displayed a spring-like elastic response. The plastic response of the aromatic-cured epoxy is attributed to the plastic folding of a local dihedral angle that is owing to the mobility discrepancy of a benzene ring and the flexible chain segments that are linked to the benzene ring. From the energy perspective, plastic dihedral-angle transitions were observed in the 1-K deformation simulations. The plastic-folding behaviors of the dihedral angles are evident near the yield point, which is coincident with the molecular-kink behaviors of the classical yielding theory.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The inelastic-deformation characteristics of epoxy polymers are understood at microscopic level. </LI> <LI> The influence of structural differences that arise from different curing agents is estimated. </LI> <LI> The plastic-folding of the dihedral angles is investigated in terms of the energy, stress, and geometric characteristics. </LI> <LI> The relative atomic displacement of local atom groups is investigated during the loading-unloading simulations. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Toward the constitutive modeling of epoxy matrix: Temperature-accelerated quasi-static molecular simulations consistent with the experimental test

Park, Hyungbum,Choi, Joonmyung,Kim, Byungjo,Yang, Seunghwa,Shin, Hyunseong,Cho, Maenghyo Elsevier Science Ltd 2018 Composites Part B, Engineering Vol.142 No.-

<P><B>Abstract</B></P> <P>We propose an efficient simulation-based methodology to characterize the quasi-static (experimental low strain rate) yield stress of an amorphous thermoset polymer, which has generally been considered a limitation of molecular dynamics (MD) simulations owing to the extremely short time steps involved. In an effort to overcome this limitation, the temperature-accelerated method – in which temperature is treated as being equivalent to time in deformation kinetics – is employed to explore the experimental strain rate conditions. The mechanical tensile behavior of a highly crosslinked polymer is then investigated with MD simulations by considering different strain rates and temperatures below the glass transition temperature. The derived yield stress represents the time- and temperature-dependent characteristics, showing that the yield stress decreases with increasing temperature and decreasing strain rate. Changeable vertical and horizontal shift factors are introduced for the first time to reflect nonlinear characteristics of the yield stress across a broad range of strain rates and to quantify the correlation between increasing temperatures and decreasing strain rates. With the proposed method, the Eyring plot, which describes the rate effect on yield from quasi-static to high-rate conditions, is predicted from MD simulations, and agrees well with macroscopic experimental results. From the constructed Eyring plot, the experimentally validated quasi-static stress-strain response is also estimated by using linear elastic model and Ludwick's hardening model. The proposed method provides new avenues for the design of glassy polymers using only fully atomistic MD simulations, thus overcoming the existing temporal scale limitations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We propose a novel approach for obtaining quasi-static yield stress and constitutive equation of amorphous polymers. </LI> <LI> This helps to overcome timescale limitations of molecular dynamics (MD) simulations. </LI> <LI> The temperature-accelerated method equates temperature with strain rate. </LI> <LI> The tensile behavior of polymers is investigated via structural analyses. </LI> <LI> We provide a new approach for the design of glassy polymers using MD simulations. </LI> </UL> </P>

고분자 소재의 소성 변형에 대한 데이터 기반 멀티스케일 해석

박형범(Hyungbum Park),한장우(Jangwoo Han),조맹효(Maenghyo Cho) 한국항공우주학회 2021 한국항공우주학회 학술발표회 논문집 Vol.2021 No.11

에폭시 폴리머의 소성 거동 모사를 위한 멀티스케일 해석 설계

박형범(Hyungbum Park),조맹효(Maenghyo Cho) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11

분자동역학 해석을 활용한 시간스케일 고려 소재 거동 및 물성 예측

박형범(Hyungbum Park) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.5

고체수소저장용 탄소나노튜브 기반 복합소재의 분자동역학 해석 기반 설계

박진우(Jinwoo Park),박형범(Hyungbum Park) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.5

후코이단/이고들빼기 혼합물에 의한 HepG2 간암세포의 apoptosis 유도

박세은(Se-Eun Park),최다빈(Dabin Choi),오교녀(Kyo-nyeo Oh),김한중(Hanjoong Kim),박형범(Hyungbum Park),김기만(Ki-Man Kim) 한국식품저장유통학회 2024 한국식품저장유통학회지 Vol.31 No.2

본 연구에서는 후코이단/이고들빼기 혼합물이 HepG2 세포의 apoptosis에 미치는 영향을 확인하고 어떠한 경로를 통해 나타나는지를 조사하였다. 후코이단/이고들빼기 혼합물이 HepG2 세포의 증식을 억제하고 세포 독성을 나타냈다. 이러한 HepG2 세포의 증식 억제 및 세포 독성이 apoptosis에 의한 효과인지를 확인한 결과, DNA fragmentation과 mitochondria membrane potential의 저해를 일으키는 것을 확인하였다. 이러한 결과를 바탕으로 HepG2 세포에서 후코이단/이고들빼기 혼합물이 apoptosis를 유도하는 기전에 관여하는 단백질의 발현 양상을 확인한 결과, intrinsic apoptosis 경로인 p53을 증가시키고, Bcl-2 family인 Bcl-2의 억제 및 BAX의 증가를 통해서 cytochrome c를 증가시켜 caspase-9 활성화하였고, caspase-3를 활성화시켜 결과적으로 apoptosis를 유도하였다. 또한, 전반적으로 후코이단/이고들빼기 혼합물의 apoptosis 유도 효과는 후코이단만 처리한 것보다 더 높은 효과를 나타냈으며, 이는 이고들빼기 추출물과의 혼합물 제조를 통해서 후코이단의 apoptosis 유도 효과가 증대되는 것으로 판단된다. 이러한 결과는 후코이단/이고들빼기 혼합물이 HepG2 세포에서 apoptosis 관련 유전자의 발현 조절에 의해 항암 효과를 나타내며, 이는 후코이단/이고들빼기 혼합물의 항암 작용의 기전을 해석하였을 뿐만 아니라, 이러한 기전 연구를 바탕으로 실질적인 간암 치료제로서의 사용 가능성을 확인하기 위해서는 유용 물질 분석 및 in vivo에서 추가 실험 등이 다양하게 수행되어야 할 것으로 판단된다. In the present study, we investigated whether a mixture of fucoidan and Crepidiastrum denticulatum extract (FCE) had the potential to improve the therapeutic efficacy of cancer treatment. The results demonstrated that FCE significantly reduced cell viability and induced the release of LDH (lactate dehydrogenase) and DNA fragmentation in HepG2 cells in a dose-dependent manner. In addition, FCE treatment also increased the protein expression level of p53, the release of cytochrome c, and the loss of mitochondrial membrane potential. Moreover, FCE dose-dependently increased protein expression levels of Bax, and cleaved caspase-3 and -9. However, FCE decreased the protein expression level of Bcl-2. These results suggest that FCE inhibits cell proliferation and induces apoptosis via the mitochondrial-mediated intrinsic pathway. The present study demonstrates that FCE can be used as an anti-cancer agent for liver cancer based on apoptosis mechanism.

식물 추출물 혼합 분말이 C2C12 세포 내 분화 및 산화적 스트레스 유발 세포사멸 조절에 미치는 효과

박세은(Se-Eun Park),최다빈(Dabin Choi),오교녀(Kyo-nyeo Oh),김한중(Hanjoong Kim),박형범(Hyungbum Park),김기만(Ki-Man Kim) 한국식품저장유통학회 2024 한국식품저장유통학회지 Vol.31 No.2

본 연구에서는 식물 추출물 혼합 분말의 근육세포 분화 및 산화적 스트레스에 대한 세포 보호 효과를 확인하고자 하였다. 추출물을 최대 1,000 μg/mL 농도까지 세포에 처리한 결과, 세포 생존율이 감소하지 않음을 확인되었다. 식물 추출물 혼합 분말이 근육세포 분화 인자에 미치는 영향을 확인하기 위해 myogenin과 MHC의 발현 여부를 확인한 결과, 무처리군에 비해 발현이 증가함을 확인하였다. H₂O₂에 의해 유도된 산화적 스트레스에 대한 세포 보호 효과를 확인한 결과, 식물 추출물 혼합 분말 처리에 의해 H₂O₂ 단독 처리군보다 세포 생존율이 증가하였으며, LDH와 creatine kinase의 활성이 감소하였다. 또한, Bax와 Bcl-2의 발현을 조절하여 caspase-9와 -3 활성화를 억제함을 확인하였다. 이를 통해 식물 추출물 혼합 분말의 근육세포 분화 효과 및 H₂O₂에 의해 유도된 산화적 스트레스에 대한 세포 보호 효과가 있음을 확인하였다. 따라서 식물 추출물 혼합 분말은 근감소증 개선을 위한 기능성 소재로써 활용이 가능할 것으로 판단되며, 향후 근감소증 개선을 위한 기능성 소재로서의 유효성 확보를 위해서 근감소증 세포 및 동물모델을 이용한 효능 및 기전 분석 연구가 더 필요할 것으로 사료된다. This study evaluated the differentiation and protective effects of mixed plant-extract powder in C2C12 muscle cells. Cells were differentiated into myotubes in 2% horse serum (HS)-containing medium with mixed plant-extract powder (MPEP) for 6 days. Treatment with MPEP increased the expression of myogenin and myosin heavy chain (MHC) protein in cells compared with non-treated cells. Differentiated cells were pretreated with MPEP, and hydrogen peroxide (H₂O₂). Our results revealed that treatment with MPEP before H₂O₂ treatment increased cell viability and decreased H₂O₂-induced lactate dehydrogenase (LDH) and creatine kinase (CK). In addition, MPEP attenuated H₂O₂-induced upregulation of Bax, downregulation of Bcl-2, and activation of caspase-9 and -3. These results suggest the MPEP can stimulate C2C12 muscle cell differentiation into myotubes and observe the protective effect of mixed plant-extract powder against muscle oxidative stress. In conclusion, MPEP may be useful as a prevention and treatment material for skeletal muscle disease caused by age-related diseases.

분자동역학 해석 기반 에폭시 고분자의 분자 구조에 따른 항복표면 규명

김진영(Jinyoung Kim),박형범(Hyungbum Park) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.11

분자동역학 해석 기반 가교율에 따른 에폭시 폴리머의 항복 표면 형상 평가

김진영,박형범,Jinyoung Kim,Hyungbum Park 한국복합재료학회 2023 Composites research Vol.36 No.5

This study focuses on investigating the influence of epoxy polymer crosslinking density, a crucial aspect in composite material matrices, on the yield surface using molecular dynamics simulations. Our approach involved generating epoxy models with diverse crosslinking densities and subjecting them to both uniaxial and multiaxial deformation simulations, accounting for the elasto-plastic deformation behaviors. Through this, we obtained key mechanical parameters including elastic modulus, yield point, and strain hardening coefficient, all correlated with crosslinking conversion ratios. A particularly noteworthy finding is the rapid expansion of the yield surface in the biaxial compression region with increasing crosslinking ratios, compared to the uniaxial tensile region. This unique behavior led to observable yield surface variations, indicating a significant pressure-dependent relationship of the yield surface considering plastic strain and crosslinking conversion ratio. These results contribute to a deeper understanding of the complex interplay between crosslinking density and plastic mechanical response, especially in the aspect of multiaxial deformation behaviors.