Abstract Absorbed moisture is a frequent contributor to performance loss in polymer-based composite structures operating in nearly all environments. However, the fundamental mechanisms that govern water-polymer interaction remain poorly understood. In this molecular dynamics study, the polarity and internal structure of an epoxy-based composite matrix was varied through manipulation of crosslink density. A commonly used epoxy-hardener combination (DGEBA- DETA) was chosen and four different models were created with crosslinking density of 20%, 51%, 65% and 81% respectively. The results indicate that the increase in crosslinking leads to a greater availability of polar sites with a concomitant rise in available free volume. The rise in network polarity aids the hydrogen bonding interactions between the absorbed water and the composite matrix, but the greater availability of free volume also allows water molecules to cluster together through mutual hydrogen bonding activity. This results in a subsequent decrease in moisture interaction with polar sites at very high crosslink densities. It was also found that the diffusivity and average dipole moment of the absorbed moisture are correlated with the state of water molecules and that a greater percentage of network-bonded molecules tends to lower both of these quantities. These results are consistent with previously published experimental results which have contemplated the dual nature of water molecules in an epoxy network. The results also highlight the potential of leveraging this phenomenon for non-destructive inspection of the physical and chemical state of a polymer network.

中文翻译：

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一项原子模拟研究，研究了受潮气污染的环氧树脂网络中不同网络结构和极性的影响

摘要 吸收水分是在几乎所有环境中运行的基于聚合物的复合结构性能损失的常见原因。然而，控制水-聚合物相互作用的基本机制仍然知之甚少。在该分子动力学研究中，环氧基复合材料基质的极性和内部结构通过控制交联密度而变化。选择了常用的环氧固化剂组合 (DGEBA-DETA)，并创建了四种不同的模型，分别具有 20%、51%、65% 和 81% 的交联密度。结果表明，交联的增加导致极性位点的更大可用性，同时可用自由体积随之增加。网络极性的增加有助于吸收水和复合基体之间的氢键相互作用，但是更大的自由体积也允许水分子通过相互的氢键活动聚集在一起。这导致随后在非常高的交联密度下与极性部位的水分相互作用减少。还发现吸收水分的扩散率和平均偶极矩与水分子的状态相关，并且网络键合分子的百分比越大，这两个量就越低。这些结果与先前公布的实验结果一致，这些结果考虑了环氧网络中水分子的双重性质。结果还突出了利用这种现象对聚合物网络的物理和化学状态进行无损检测的潜力。