A combined mechanical, microscopic and local electrochemical evaluation of self-healing properties of shape-memory polyurethane coatings

In the present paper, a shape-memory polyurethane (SMPU) film consisting of a two-segmented block co-polymer is presented as a novel organic coating for the protection of metals against corrosion. When the coating is damaged, a physical self-healing and consequent recovery of the barrier properties are induced after an increase of the temperature. Indeed, thermal treatment leads to the relaxation of the soft matrix in the polymer and subsequent coverage of the damaged area. The scanning vibrating electrode technique (SVET) is employed to visualize local variations of the electrochemical activity in the damaged area of the SMPU coating, proving that the physical-repairing of the film during the thermal treatment leads to a recovery of the protective properties of the coated system. By using laser scanning confocal microscopy (LSCM), observation of the coating defect before and after the thermal healing allowed to establish the efficiency of the polymer to cover the coating defect qualitatively. Complementary experiments using dynamic mechanical analysis (DMA) allowed to study the mechanical properties of the co-polymer under a gradient of temperature and to prove its stability during the healing treatment.