Understanding the multifunctional anticorrosion protective mechanism of epoxy-based coatings modified with hydrogel and benzotriazole conveying nanotubes for Q235 steel protection in 3.5 % NaCl

Coatings with multiple protective properties are highly desired for anti-corrosion purposes as they overcome the limitations of conventional coatings that have limited functionality in field applications. Thus, this study describes the protective mechanisms of a new class of composite coatings fabricated by embedding benzotriazole (BTA) laden nanotubes prior-functionalized with interfacial wrappings of chitosan hydrogel (CTSH) entrapping excess crosslinking agents (glutaraldehyde (GTRA) or epichlorohydrin (EPIH)) in epoxy (E44) matrix cured with polyamide. The modification led to an improvement in the barrier and physical properties of the composite coatings and introduced shape-memory self-repairing capabilities. Long-term impedance spectroscopy (EIS) complemented with the physical property tests was employed to interrogate the improved barrier properties. The coatings' microstructure and composition analyzed with SEM and EDS reveal the shape-memory self-repairing effect which was further characterized with overtime optical snapshots of samples exposed in a salt-spray chamber. The antibacterial functionality of the composite coatings against some marine bacteria (Marinobacter aquaeolei and Marinobacter salsuginis) was characterized using combined SEM and confocal laser scanning microscopy (CLSM). UV–visible spectrophotometry data reveal the pH-responsive release of the entrapped functional materials from the composite coatings. The experimental findings show that the new composite coatings exhibited intriguing triple-action protective functionalities and were more effective in protecting Q235 carbon steel exposed to 3.5 % NaCl compared to the conventional epoxy coating. This suggests that comparatively, the composite coatings have promising applications in structures that are exposed to sea environments.