Nonempirical Kinetic Modeling of Non-fickian Water Absorption Induced by a Chemical Reaction in Epoxy-Amine Networks

In the last two decades, several studies made in our laboratory have shown that hydrolytic reactions may occur during water absorption and may be responsible for behavioral deviations from the classical Fick’s law in epoxy-amine networks. On one hand, water is chemically consumed by specific groups initially present in the repetitive structural unit (e.g., unreacted epoxies and amides) or formed by oxidation under operating conditions. On the other hand, water establishes strong molecular interactions (hydrogen bonds) with new highly polar groups resulting from hydrolysis (alcohols and acids). Due to both contributions, the kinetic curves of water absorption no longer tend towards an equilibrium value, i.e., a final saturation plateau, but display a slow and continuous increase over time in the water mass uptake. On this basis, a diffusion/reaction model has been developed for predicting such a peculiar water sorption behavior. In addition, the classical Henry’s law has been modified for describing the changes in boundary conditions during the course of the hydrolytic reaction. This chapter provides an overview of the recent theoretical advances made in this field and demonstrates, through two case studies, the good predictive value of the kinetic modeling approach set up in our laboratory.