Moisture uptake in organic coatings monitored with EIS

Although EIS is widely applied as a technique for monitoring the degradation of polymeric coatings when exposed to acqueous environments, a rigourous theoretical framework has not yet been fully developed. In this paper a mathematical model relating the kinetics of moisture uptake to the changes in the dielectric properties of organic coating is presented and a correlation between the extent of absorbed water and changes in the coating capacitance is developed Thus, it is possible to measure both water diffusivity and solubility from capacitance data, making this technique very attractive as an alternative to the gravimetric method for investigating the barrier properties of organic coatings. The model developed in this paper was then employed to interpret the behaviour of industrial electrogalvanized iron sheet coated with a water based epoxyphenolic paint when exposed to an aqueous sodium chloride solution at room temperature.