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Correlation between the physical structure of a commercially formulated epoxy paint and its electrochemical impedance response

Abstract : In the present work, a commercial high solids epoxy-based paint used for the corrosion protection of steel was characterized by electrochemical impedance spectroscopy (EIS). The aim was to analyze the influence of water absorption on the physical structure of the paint, through the impedance data analysis. First, the water uptake was followed by gravimetric measurements on free-standing films as a function of the exposure time to a 0.5 M NaCl solution. Gravimetric measurements indicated a mass loss, linked to a release of a plasticizer from the formulation. This compound was dosed in the NaCl solution. The water volume fraction was also determined from the high-frequency part of the impedance diagrams, employing a linear rule of mixtures. The water fraction values obtained from the two methods were in acceptable agreement. The glass transition temperature (Tg) was determined by differential scanning calorimetry for the dry coating as well as for the coating after different immersion times in the NaCl solution. The use of the dielectric permittivity formalism allowed the mean relaxation times to be obtained from the impedance data analysis. The real part of the electrical conductivity was also considered. The variation of these parameters values as a function of the exposure time to the NaCl solution, was correlated with the Tg variation. They accounted for plasticization at the beginning of immersion (water uptake) and antiplasticization for longer exposure times (plasticizer release). For the studied system, it was possible to extract parameters representative of the molecular mobility from the impedance spectra analysis and to link them to the modification of the coating’s physical structure.
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Submitted on : Wednesday, June 24, 2020 - 10:42:38 AM
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Aurélien Roggero, Laura Villareal, Nicolas Caussé, Audrey Santos, Nadine Pébère. Correlation between the physical structure of a commercially formulated epoxy paint and its electrochemical impedance response. Progress in Organic Coatings, Elsevier, 2020, 146, pp.105729. ⟨10.1016/j.porgcoat.2020.105729⟩. ⟨hal-02879691⟩

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