Morphology effect on water sorption behavior in a thermoplastic modified epoxy resin system

Water sorption behavior in polyetherimide (PEI) modified diglycidyl ether bisphenol-A/4,4′-diaminodiphenyl sulfone (DGEBA/DDS) systems was investigated by gravimetric analysis, positron annihilation lifetime spectroscopy and scanning electron microscopy. The equilibrium water uptake showed strong composition-dependent, which suggested that hydrophilic groups rather than free volume were more significant in determining ultimate water sorption. While besides the number of hydrophilic groups and fractional free volume, morphology induced by phase separation was another key factor that decided the value of diffusion coefficient, which was chiefly responsible for the anomalous diffusion behavior observed at the beginning of co-continuous phase. In addition, morphology not only had the function of decreasing fractional free volume, but also changed the number of hydrophilic groups in epoxy rich regions, which obviously distinguished water sorption behavior in the blends from that in single component systems.