Visualization of the self-healing process by directly observing the evolution of fluorescence intensity

Abstract

Self-healing is a process in which the non-equilibrium state caused by mechanical damage gradually evolves toward the equilibrium state. However, tracking this process is highly challenging. Here, we copolymerize a fluorophore (TC1) with a strong aggregation-caused quenching (ACQ) effect in a self-healing elastomer with a dynamic hydrogen-bonded network. We find that TC1 is highly sensitive to the local chain packing environment and thus can detect the subtle microstructural change induced by mechanical damage and self-healing. Confocal laser scanning microscopy reveals that the fluorescence intensity evidently increases around the fracture surface and scratch, indicating that the mechanical damage induces a slight decrease of chain packing efficiency. Upon annealing the fracture surface for a certain period of time before healing, both the fluorescence intensity and healing efficiency decrease with time, and interestingly there is a linear relationship between them. If the scratch is allowed to heal at room temperature, the fluorescence intensity around the scratch also decreases linearly with time until the contrast between the scratch and normal surface becomes hardly distinguishable. Therefore, this work provides a novel way to study the self-healing process of dynamically crosslinked materials.