An FTIR/ATR in situ study of sorption and transport in corrosion protective organic coatings - 1. Water sorption and the role of inhibitor anions

Both sorption and desorption transport coefficients of water and the inhibitor (HPO42-) in a series of epoxy resins (model paints) of different cross-linking density have been reported. Water diffusion is unaffected by low electrolyte concentrations (0. 1 mum) but is retarded at 0.6 M chloride ion levels, presumably due to water-polymer-polymer interaction shielding. Swelling is small, but may be significant for polymer chain relaxation. The FTIR data have been used to add a molecular level interpretation of the four different pseudo-Fickian processes observed at room temperature. These data are consistent with rapid sorption onto polymer active (OH, NH), sites followed by slower incorporation of water into polymer microvoids where cluster sizes are smaller. The reverse process (on desorption) is also evident from the water, v(OH), spectral distribution. No evidence of significant accumulation of 'bulk' water at the polymer-substrate interface was found. (C) 2003 Elsevier B.V All rights reserved.