Self-healing epoxy coatings with microencapsulated ionic PDMS oligomers for corrosion protection based on supramolecular acid-base interactions

To obtain a self-healing coating and improve the corrosion resistance of coated low-carbon steel surfaces, a commercial epoxy coating was modified by adding microcapsules composed of a poly(methyl methacrylate) shell and a core of ionic polydimethylsiloxane (PDMS) oligomers. The encapsulation of amino- and carboxylic acid-terminated PDMS was achieved by a solvent evaporation process after the emulsification of core and shell materials, dissolved in CH2Cl2, in a suitable colloidal solution. A high core loading of nearly 50% wt. was successfully obtained by carefully increasing the interfacial tension of oil-in-water emulsion before the solvent evaporation. The microcapsule morphology was evaluated by SEM and optical microscopy analyses, which showed a particle diameter range of 20–70 μm. The presence of ionic PDMS oligomers as core materials was demonstrated by FTIR spectroscopy and thermogravimetric analysis (TGA), which was also employed to determine the core loading. The newly prepared microcapsules were then incorporated into the matrix of a commercial two-component epoxy coating. Corrosion protection abilities were assessed by comparing samples coated with a standard epoxy coating modified with a 20% wt. of microcapsules and the pristine epoxy coating. The corrosion protection performance of the modified coating was evaluated through electrochemical impedance spectroscopy (EIS) tests and potential vs time measurements, which showed that the microcapsules in the coating matrix caused a beneficial increase in barrier properties of a scratched coating. The surface damage triggered the release of functional PDMS oligomers, leading to the formation of a supramolecular ionic network and providing self-healing abilities to the modified coating.