An FTIR/ATR in situ study of sorption and transport in corrosion protective organic coatings: Paper 2. The effects of temperature and isotopic dilution

A detailed temperature variation (18-50°C) FTIR/ATR study of sorption and desorption of water into a series of cured epoxy resins has been reported. For higher temperatures (35-50°C) the data were modelled with a single Fickian diffusion equation, giving an increased D as the temperature increased and an activation energy (EA) in the 55-60kJmol-1 region. At lower temperatures (18-35°C) - well-below the Tg - a two-stage sorption equation was needed and the apparent EA was negative. This is probably associated with changes in water clustering among the distributed 'voids' in the glassy polymer associated with chain relaxation at extended times. The use of D2O as a penetrant allowed diffusion coefficient measurements for highly dense epoxy matrices, where FTIR/ATR cannot detect the ν(OH) band of water over and above the residual polymer-OH groups (in the dry state). The data for the D2O studies were notably influenced by isotopic exchange; which was found to be a diffusion controlled process, even in a polymer matrix. © 2003 Elsevier B.V. All rights reserved.