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Nonaqueous room-temperature ionic liquids (RTILs) offer a method of using electrochemical impedance spectroscopy (EIS) to analyze coatings without the confounding effects, such as plasticization, associated with an aqueous working fluid. Thermal cycling has been used as an accelerated testing method for ranking the corrosion protection of coatings. The influence of thermal cycling on the degradation of a coating was investigated using a hydrophilic RTIL as the electrolyte for the drying cycle of EIS experiments. The change in diffusion coefficient, saturated water volume fraction, and activation energy for the absorption and desorption of water by the coating was obtained. [ABSTRACT FROM AUTHOR]

The capacitance evolution of an organic coating undergoing cyclic wetting and drying conditions was monitored by single frequency electrochemical impedance spectroscopy. Monitoring of the drying condition was possible with the use of a hydrophilic room temperature ionic liquid and the methodology employed is presented. Experimental results associated with cyclic dilute NaCI wetting and ionic liquid drying are presented for an epoxy coating on an AA 2024-T3 substrate. The calculated capacitance evolutions associated with wetting and drying were generally consistent with Fick's second law. The calculation of the water ingress and egress diffusion coefficients using a short-time approximate solution and a series solution to Fick's second law are presented. The latter solution is shown to address the capacitance evolution better than the former with the ingress coefficient larger than the egress coefficient for a given exposed coating surface. There was agreement between the calculated diffusion coefficient ingress values for coating areas exposed to cyclic NaCI wetting—ionic liquid drying and cyclic NaCl wetting—natural drying conditions. Comparison of the impedance spectra for test areas indicated that the use of the ionic liquid as a drying medium influenced the electrochemical properties of the coating only after a number of cycles. [ABSTRACT FROM AUTHOR]