Monitoring crack appearance and healing in coatings with damage self-reporting nanocapsules

Autonomous highlighting of damage in protective polymer coatings allows on-demand maintenance and enables prolongation of the lifetimes of the coated materials. To monitor the entire cycle of damage occurrence and successful healing, one must be able to visualize both processes and display the current health-state of the coating. Herein, we equipped coatings with nanocapsules that can self-indicate their mechanical micro-damage via color development. Hence, whenever the coating was damaged, the capsules broke and highlighted the damaged spot. As a second feature, the color development was reversed and discoloration occurred in the presence of (self-)healing compounds, allowing the user to monitor the healing process. Thus, in the first step, damages were highlighted via color “turn-on” and in the subsequent step a propagating healing reaction “turns-off” the damage indication system to trace the healing reaction and allow monitoring of the entire health cycle.