In this work, the correlation between electrolyte transport properties and the variation of pigment volume concentration (PVC) in a series of organic coatings is explored. Using an odd random phase electrochemical impedance spectroscopy (ORP-EIS) approach, the diffusion of ions independent from water take-up is analysed. A higher PVC resulted in a more homogeneous coating morphology, which could be associated with a faster diffusion of ions following a Fickian regime and enhanced water uptake. In the case of lower pigment loading, the obtained heterogenous morphology of the coating introduced new challenges to the physical interpretation of the proposed electrochemical equivalent circuit.

In this work, a new finite element modelling (FEM) approach is followed to model spatiotemporally resolved water uptake in organic coatings. To this aim, we start from a physical model, where not only Fickian diffusion of water is taken into account but also the adsorption/desorption reaction of water on the polymer matrix. Starting from a number of important coating properties and crucial model parameters, derived from gravimetric and Fourier transform infrared (FTIR) measurements as the model input, the local water concentration over the coating thickness as a function of time is modelled for a polyethylene glycol diacrylate (PEGDA) coating. The modelled water concentration is then used to calculate virtual capacitance values which are evaluated against experimental capacitance values extracted from impedance measurements. The constraints of the FEM model and ORP-EIS experiments and the discrepancies between them are critically discussed in order to carry out a meaningful model validation, eventually leading to model improvements.