Smart Materials with Dual Functionality: Repeatable Damage-Detection and Self-Healing

Polymer materials are extensively used because of theirexcellentperformance; however, when used for a long time, they break and eventuallylose their original properties. Thus, smart polymer materials thatcan repeatedly detect and repair damage must be urgently developedto increase their durability and lifespan. In this study, a smartmaterial with dual functionality (damage-detection and self-healing)is developed via a facile method of incorporating spiropyran (SP)beads, which exhibit changes in color and fluorescence when damaged,into a Diels-Alder (DA)-based self-healing matrix. When polyurethane(PU) is added to the DA-based matrix, the dual functionality exhibitsa strong dependence on the proportion of PU. Because the PU ratioaffects two opposing factors (damaged area and load-bearing capacity),the damage-detecting ability exhibits the best performance at 40 wt% PU, where both factors are optimized. A high healing efficiencyof 96% is achieved via a dynamic DA reaction. In particular, the repeatabilityof the dual-functionality is successfully attained through the reversibilityof the SP beads and DA networks, where the detection and healing efficienciesare reduced by 15 and 23%, respectively, after 10 cycles. Furthermore,the reprocessed fractured specimens exhibit excellent recyclability.