Scientists from the University of Groningen in the Netherlands and the University of Pisa in Italy have developed a method for fluorescence-based monitoring of self-healing Diels-Alder networks. The technique can track changes in chemical cross-linking after self-healing plastics are heated or processed.
The study, led by Paul van den Tempel and his co-workers, examined polymer materials that repair themselves through reversible chemical bonds. Self-healing materials using Diels-Alder chemistry can form and break these bonds repeatedly when exposed to heat, allowing the network to change during processing and repair.
Measuring these changes can be challenging because Diels-Alder reactions produce two stereoisomers. Their proportions can also change according to the material’s thermal history. The new fluorescence method provides a way to measure reaction conversion without physically disturbing the material.
The researchers added a small amount of maleimide-functionalized tetraphenylethylene, known as TPE, to furan-maleimide systems. TPE has aggregation-induced emission properties.
This phenomenon, called restriction of rotation, boosts fluorescence. The materials had different cross-link densities and gelation temperatures, yet their fluorescence changed in a predictable way during heating.
The fluorescence response also remained reversible over several heating cycles. Its normalized intensity followed the same pattern as the simulated reaction conversion. The response remained reversible even when the material was designed to melt during heating.
