Reactive Molecular Dynamics Study of Hygrothermal Degradation of Crosslinked Epoxy Polymers
Reactive Molecular Dynamics Study of Hygrothermal Degradation of Crosslinked Epoxy Polymers
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DOI：
10.1021/acsapm.2c00383
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发表时间：
2022-06-10
影响因子：
5
通讯作者：
Rasulev, Bakhtiyor
中科院分区：
文献类型：
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作者：
Karuth, Anas;Alesadi, Amirhadi;Rasulev, Bakhtiyor
环氧热固性树脂在各种应用中经常暴露在高湿度环境中，根据环境的不同经历可逆和不可逆的降解。这项研究提出了一个反应分子动力学(MD)模拟框架，以更深入地了解湿热老化过程，这对于开发一种有针对性的方法来对抗环氧热固性树脂的水辅助降解至关重要。通过施加ReaxFF电势，在低温下创建了环氧胺网络，以避免不必要的高温副反应，在高温副反应中添加水分子以达到所需的水分污染程度。模拟结果表明，除了湿气进入的增塑作用外，由于水分子与网络中的负电性中心的多位相互作用，环氧网络的力学性能和密度也有所恢复。此外，长期暴露在湿度中或由于开裂而直接暴露会导致环氧胺网络发生不可逆转的变化。应用反应性分子动力学模拟方法，成功地模拟了环氧胺网络中水分子的质子化和醚键C-O键的亲核攻击。值得注意的是，模拟结果表明，水分子在环氧网中的选择性取决于环氧网的空间排列和空间位阻。这项工作通过阐明网络的自由体积和网络极性之间的相互作用，为湿热老化提供了分子水平的见解，为在潮湿环境中提高环氧热固性的耐久性和性能的先进设计策略铺平了道路。
Epoxy thermosets are often exposed to high humidity environments in various applications, undergoing reversible and irreversible degradation depending on the environment. This study presents a reactive molecular dynamics (MD) simulation framework to gain deeper insights into the hygrothermal aging process, which is essential to develop a targeted approach to combat water-assisted degradation in epoxy thermosets. By applying ReaxFF potential, an epoxy-amine network is created at low temperatures to avoid unwanted hightemperature side reactions, where the water molecules are added to achieve the desired degree of moisture contamination. The simulations show that in addition to the plasticization effect from the moisture ingress, the epoxy network shows recovery in mechanical properties and density due to the multi-site interaction of the water molecule with the electronegative sites within the network. Moreover, long-term exposure to humidity or direct exposure due to cracking can induce irreversible changes in the epoxy-amine network. The protonation of the water molecule and nucleophilic attack on the C-O bond of the ether linkages in the epoxy-amine networks are successfully simulated by applying reactive MD simulations. Remarkably, the simulations show that the selectivity of water molecules for the hydrolysis reaction in the epoxy network depends on the spatial arrangement and the steric hindrance of the network. This work provides molecular level insights into hygrothermal aging by elucidating the interplay between free volume and polarity of the network in the physical aging of the moist epoxy networks, paving a way for advanced design strategy toward better durability and performance of epoxy thermosets in humid environments.