Vibrational Spectroscopy Evidence for the Dual Nature of Water Sorbed into Epoxy Resins

The physical interactions occurring between absorbed water molecules and the network of a tetrafunctional epoxy resin were studied by mid-infrared (MIR) and near-infrared (NIR) Fourier transform spectroscopy. The spectrum of the sorbed water molecules was isolated in both frequency ranges and the assignments of the various components of the spectrum were proposed accordingly. The results of the vibrational analysis reaffirm the existence of two populations of penetrant molecules, a mobile variety residing within microvoids and those strongly bound to the polymeric network through hydrogen bonding interactions. A comparative analysis of the NIR spectra makes it also possible to deduce the most likely structures of these adducts and their stoichiometry. Finally a method was identified for the quantitative estimation of the bound water responsible for the plasticization of the matrix.