Self-healing polymer coatings

Inspired by biological systems in which damage triggers an autonomic healing response, structural polymeric materials have been developed that possess the ability to self-heal. First generation self-healing composites incorporate healing agent filled microcapsules and catalyst particles in an epoxy matrix. Although high healing efficiencies have been achieved using this concept, only a limited supply of healing agent is available. If the same crack were to open again, in general a second healing would not be possible. In this paper, we report on a second generation of self-healing composites that utilize an interconnected microvascular network to flow healing agent throughout the matrix. This concept is applied to heal a coating on a substrate containing a microchannel network. A new protocol is developed for coated networks, which entails testing virgin samples in four-point bending until cracks initiate in the coating. The onset of cracking leads to a distinct load drop and corresponding decrease in the bending stiffness. The sample is then allowed to heal (healing agent from the channels permeates the cracks and interacts with a catalyst suspended in the coating) and is retested. The results from this microvascular system are compared with appropriate controls as well as healing efficiencies of a microcapsule coating system.