Hydrolysis degradation mechanisms of epoxy resin coatings on concrete in hydrothermal environment resolved by molecular dynamic simulations

Organic coatings are prone to hydrolysis under hydrothermal environments, however, the mechanisms remain still far from being fully understood. Herein, molecular dynamic simulations are performed to explore the structural degradation of an epoxy resin by hydrolysis and its performances. This study quantifies the changes of water molecule clusters and hydrogen bond networks, and explores the relationship between structural change and performance degradation . The results show that after hydrolysis, epoxy molecules change from chemical bonds to intermolecular forces, weakening molecular interactions. The hydrogen bond network plays a crucial role in maintaining performance. The new hydroxyl groups formed after hydrolysis exhibit strong hydrogen bonding effects, reducing large molecular clusters and disrupting the hydrogen bond network. This increases the system's flexibility and further degrades material performance. After hydrolysis degradation, the linear thermal expansion coefficient of the epoxy resin coating is nearly 7–10 times that of concrete, generating strong thermal discrepancy stresses, and causing coating-substrate delamination . The findings deepen understandings in hydrolysis degradation of epoxy resin on concrete substrate under hydrothermal environments in molecular scales . In practice, epoxy resin of higher water tolerance and lower thermal expansion is suggested to be used in hydrothermal environments. • Hydrolysis of epoxy resin degrades both mechanical and thermal properties. • Hydrolysis raises hydroxyl groups and polarity, but depresses water clustering. • Thermal discrepancy stresses may cause concrete-epoxy delamination .