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.

A spectro-electrochemical setup of Fourier transform infrared spectroscopy (FTIR) in the Kretschmann geometry and odd random phase multisine electrochemical impedance spectroscopy (ORP EIS) is applied to in situ monitor the effect of an aqueous electrolyte on the polymer/metal oxide interface. The interfacial interactions of an ultrathin polyacrylic acid (PAA) film on an aluminum oxide surface are identified as carboxylate ionic bonds and changes induced by the effect of water diffusion at the interface are monitored in situ. Initially after electrolyte exposure, an increase in ionic bonding is observed. However, eventually the interfacial interactions are replaced by water molecules, leading to macroscopic delamination. By comparing a variation of oxide types, the stability of the interfacial bonds is linked to the amount of free hydroxyl groups on the aluminum oxide surface. An electric equivalent circuit is proposed to model the ORP EIS response of the PAA/aluminum oxide system and the fitted resistance values could be interpreted in a physically meaningful way. Finally, a poly(methyl methacrylate) (PMMA) deposition on aluminum oxide is investigated to explore the effect of a variation in functional groups present at the polymer/metal oxide interface. It is shown that PMMA forms a more stable interface than PAA on native aluminum oxide. This work demonstrates that IR spectroscopy in the Kretschmann geometry and ORP EIS are suited techniques to in situ probe interfacial bonds at polymer/metal oxide systems exposed to aqueous conditions. Moreover, a variation of the surface properties of the metal oxide as well as the functional groups of the polymer alter the stability of their mutual interface when exposed to aqueous conditions.