Lehrstuhl für Theoretische Chemie/Computer Chemie Centrum, Friedrich-Alexander Universität Erlangen-Nürnberg, Nägelsbachstraße 25, 91052, Erlangen, Germany.
J Mol Model. 2023 Jul 12;29(8):243. doi: 10.1007/s00894-023-05654-w.
We report on atomic level of detail analyses of polymer composite models featuring epoxy resin interfaces to silica, iron oxide, and cellulose layers. Using "reactive" molecular dynamics simulations to explore epoxy network formation, resin hardening is investigated in an unprejudiced manner. This allows the detailed characterization of salt-bridges and hydrogen bonds at the interfaces. Moreover, our sandwich-type composite systems are subjected to tensile testing along the interface normal. To elucidate the role of relaxation processes, we contrast (i) direct dissociation of the epoxy-metal oxide/cellulose contact layer, (ii) constant strain-rate molecular dynamics studies featuring (visco-)elastic deformation and bond rupture of the epoxy resin, and (iii) extrapolated relaxation dynamics mimicking quasi-static conditions. While the fracture mechanism is clearly identified as interface dissociation of the composite constituents, we still find damaging of the nearby polymer phase. The observed plastic deformation and local cavitation are rationalized from the comparably large stress required for the dissociation of salt-bridges, hydrogen bonds, and van der Waals contacts. Indeed, the delamination of the contact layers of epoxy resins with slabs of silica, magnetite, and cellulose call for a maximum stress of 33, 26, and 21 MPa, respectively, as compared to 84 MPa required for bulk epoxy yielding.
Molecular dynamics simulations using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code were augmented by a Monte Carlo-type procedure to probe epoxy bond formation (Macromolecules 53(22): 9698-9705). The underlying interaction models are split into conventional Generalized Amber Force Fields (GAFF) for non-reacting moieties and a recently developed reactive molecular mechanics potential enabling epoxy bond formation and cleavage (ACS Polymers Au 1(3): 165-174).
我们报告了聚合物复合材料模型的原子级分析，这些模型具有与二氧化硅、氧化铁和纤维素层的环氧树脂界面。使用“反应性”分子动力学模拟来探索环氧树脂网络的形成，可以公正地研究树脂的硬化。这允许对界面处的盐桥和氢键进行详细的特征描述。此外，我们的三明治型复合体系沿着界面法线进行拉伸测试。为了阐明松弛过程的作用，我们对比了 (i) 环氧树脂-金属氧化物/纤维素接触层的直接解离，(ii) 具有环氧树脂的（粘弹）变形和键断裂的恒应变速率分子动力学研究，以及 (iii) 模拟准静态条件的外推松弛动力学。虽然断裂机制显然是复合材料成分的界面解离，但我们仍然发现附近聚合物相受到损伤。从解离盐桥、氢键和范德华接触所需的相对较大的应力出发，可以合理地解释观察到的塑性变形和局部空化。事实上，与块状环氧树脂所需的 84 MPa 相比，环氧树脂与二氧化硅、磁铁矿和纤维素薄片的接触层分层需要的最大应力分别为 33、26 和 21 MPa。
使用大规模原子/分子大规模并行模拟器 (LAMMPS) 代码的分子动力学模拟通过蒙特卡罗型程序得到增强，以探测环氧树脂键的形成 (Macromolecules 53(22): 9698-9705)。基础的相互作用模型分为用于非反应部分的常规广义 Amber 力场 (GAFF) 和最近开发的能够形成和断裂环氧树脂键的反应分子力学势 (ACS Polymers Au 1(3): 165-174)。
