Investigating the effect of chemical structures on water sorption and diffusion in amine-cured epoxy resins by molecular dynamics simulations

Mechanical degradation of polymer materials by moisture ingress is inevitable due to their chemical and physical properties. In this regard, it is necessary to better understand the mechanisms governing interactions between water and polymer. In this research, the sorption and diffusion of moisture in epoxy systems with different chemical structures of amines (DGEBA/DDS and DGEBA/DDM) has been investigated by molecular dynamics simulations. For the validation, the physical properties of the simulation models and the calculated values of the diffusion coefficient and equilibrium water content have been compared with the existing data and acceptable results have been obtained. The study results of polymer systems showed that both the polarity and the average radius of nanopores played an effective role in diffusivity and equilibrium water content values. It was also found that the interactions between water and polymer molecules at the water-polymer interface played an important role in the initiation of the moisture sorption process. The results of the simulation during the hydrothermal aging process showed that moisture first entered the pores in the epoxy network, then diffused deeper into the polymer, and finally, with a change in the polymer structure, caused water-polymer hydrogen bonds with stronger strength.