Characteristics of water absorption in amine-cured epoxy networks: a molecular simulation and experimental study

Moisture corrosion of cured epoxy resins seriously affects the durability of epoxy products and has been a serious issue in scientific and engineering fields. In this study, a series of cured epoxy resins with different structures were prepared by tuning their curing conversion in both experimental and simulation methods. In experiments, the equilibrium water content and the diffusion coefficient of amine-cured epoxy resins were measured by gravimetric measurement. The interaction between water molecules and epoxy network was investigated by time-resolved FTIR, difference spectroscopy and 2D correlation spectroscopy. In simulation, the hydrogen bonds, the mobility of hydroxypropyl ether groups and water molecules, and the free volume with its distributions were analyzed. Five types of water molecules were intuitively observed in this study; free volume had a stronger influence on equilibrium water content than polarity in the bifunctional epoxy/amine system, and the increase in the diffusion coefficient was considered as the result of reduction in motion resistance and an increase in channels for the motion of water molecules.