NIR light-triggered self-healing waterborne polyurethane coatings with polydopamine-coated reduced graphene oxide nanoparticles

Self-healing coatings that are able to self-repair after being damaged represent an effective solution to provide a reliable and long-lasting protection of the underlying substrate. In this work, we developed self-healing waterborne polyurethane (PU) coatings through the introduction of Diels-Alder bonds in the polymer backbone. Although heat is typically used as trigger, here we exploited photothermal converters to allow also NIR light-induced self-healing. To this aim, we synthesized (3-aminopropyl)-triethoxysilane-modified graphene oxide nanosheets that were subsequently coated by nanometric polydopamine particles, which serve for imparting to the coating the NIR-responsive self-healing feature. Fourier transform infrared and X-ray photoelectron spectroscopy confirmed the successful synthesis of PDA-coated reduced graphene oxide nanoparticles, which were thus exploited to prepare nanocomposite PU coatings on bronze substrates on which they exhibited good adhesion. Once scratched, fast and effective self-healing was ensured upon irradiation with NIR light for only 30 s. In addition, electrochemical impedance spectroscopy analyses proved that the nanocomposite coatings exhibited improved barrier properties which resulted in an enhanced protection of the underlying metal from corrosion.