The diffusion mechanism of water transport in amine-cured epoxy networks.

In the present work, time-resolved attenuated total reflection Fourier transform infrared spectroscopy (ATR-IR), near-infrared (NIR) spectroscopy, and generalized two-dimensional (2D) correlation analysis were used to investigate water diffusion processes and the state of water molecules in six different epoxy resins. Positron annihilation lifetime spectroscopy (PALS) experimental results and IR results suggested that water diffusion is controlled by local chain reorientation and bond dissociation of water molecules from epoxy networks. Dynamic mechanical analysis (DMA) results of glass transition temperatures of epoxy resins after immersion in hot water correlated well with the PALS and IR results. In addition, four types of water molecules, termed nonbonded (S(0)), single bonded (S(1)), loosely double hydrogen bonded (S(2L)), and tightly double bonded (S(2T)), were detected. It was likewise found, as verified by rough estimation, that water molecules with double hydrogen bonds mostly accomplished diffusion.