Characterisation of water-based coatings by electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy was used to investigate the behaviour of an epoxy water-based coating immersed in a solution of sodium chloride. The increase of the resistance, associated to the high-frequency part of the diagram (R-HF), with increasing immersion time was attributed to the occurrence of coalescence of the polymer particles in water-based film, accelerated by immersion in the electrolytic solution. It was shown that the capacitance (C-HF) variation with immersion time results from a plasticisation effect induced by water uptake and from the coalescence process. In addition, dielectric measurements revealed that the water molecules are bound with the polar groups of the polymer. (C) 2002 Elsevier Science B.V. All rights reserved.