Konrad Julian, Moretti Paolo, Zahn Dirk
Lehrstuhl für Theoretische Chemie/Computer Chemie Centrum, Friedrich-Alexander Universität Erlangen-Nürnberg, Nägelsbachstraße 25, 91052 Erlangen, Germany.
Institute of Materials Simulation, Friedrich-Alexander-Universität Erlangen-Nürnberg, Dr.-Mack-Str. 77, 90762 Fürth, Germany.
Polymers (Basel). 2022 Sep 28;14(19):4069. doi: 10.3390/polym14194069.
In this study, we unravel the atomic structure of a covalent resin near boundaries such as surfaces and composite constituents. For this, a molecular simulation analysis of epoxy resin hardening under various boundary conditions was performed. On the atomic level of detail, molecular dynamics simulations were employed to study crosslinking reactions and self-organization of the polymer network within nm scale slab models. The resulting structures were then coarsened into a graph theoretical description for connectivity analysis of the nodes and combined with characterization of the node-to-node vector orientation. On this basis, we show that the local bonding of epoxy resins near interfaces tends to avoid under-coordinated linker sites. For both epoxy-vacuum surface models and epoxy-silica/epoxy cellulose interfaces, we find almost fully cured polymer networks. These feature a local increase in network linking lateral to the surface/interface, rather than the dangling of unreacted epoxy groups. Consequently, interface tension is low (as compared to the work of separating bulk epoxy), and the reactivity of the resin surface appears negligible.
在本研究中，我们解析了靠近诸如表面和复合材料成分等边界处的共价树脂的原子结构。为此，我们对环氧树脂在各种边界条件下的硬化过程进行了分子模拟分析。在原子层面的细节上，采用分子动力学模拟来研究纳米尺度平板模型内聚合物网络的交联反应和自组织。然后将所得结构粗化为用于节点连通性分析的图论描述，并结合节点到节点向量取向的表征。在此基础上，我们表明环氧树脂在界面附近的局部键合倾向于避免配位不足的连接位点。对于环氧 - 真空表面模型和环氧 - 二氧化硅/环氧纤维素界面，我们发现聚合物网络几乎完全固化。这些特征表现为网络连接在表面/界面横向局部增加，而非未反应环氧基团的悬空。因此，界面张力较低（与分离本体环氧树脂的功相比），并且树脂表面的反应性似乎可以忽略不计。
