Stimuli-responsive Polyelectrolyte Multilayers for fabrication of self-healing coatings - A review

This review provides a comprehensive discussion and highlights the recent progress for the utilization of Polyelectrolyte Multilayers (PEMs) as stimuli-responsive components for fabrication of coatings with smart self-healing functionality. The demand for self-healing coatings is rapidly growing due to their great potential to diminish degradation and reduce the maintenance cost. PEMs, constructed via different layer-by-layer assembly technologies, represent one of the most promising smart materials for fabrication of healable coatings. Based on the nature of the employed components for multilayer fabrication (e.g. polyelectrolytes, nanoparticles, inhibitors), PEMs have the ability to provide unique or multiple-responsive functionality, stimulated by different triggering mechanisms (e.g. pH, temperature, light), for effective and controlled on-demand release of corrosion inhibitor. Different approaches have been adapted for utilizing the responsive-PEMs as key component for developing protective coatings with active feed-back functionality. The first approach is based on the incorporation of inhibitor-loaded nanocontainers coated with PEM shells as the smart self-healing component in the formulated coating matrix (e.g. sol-gel or epoxy based coating). Various nanocontainers coated with PEM shells have been used including hollow PEM capsules, silica nanoparticles, mesoporous silica and titania nanoparticles, halloysite nanotubes and layered-double hydroxides. The second approach is based on the direct deposition of the PEMs/inhibitor complexes onto the metal surface. In the latter case, the self-healing action of PEMs is based on multiple and synergistic mechanisms.