In a recent issue of Advanced Materials, a research team led by Joris Sprakel from Wageningen University and Sybrand van der Zwaag from Delft University of Technology in the Netherlands, visualized the molecular cascade of autonomous repair in a self-healing polymer for the first time. They showcased how a quantitative implementation of a medical imaging technique, utilizing the interaction of laser light with nanoparticles embedded in the polymer, can provide detailed micromechanical images of the material as a damaged spot spontaneously heals. With this novel approach, the authors visualized, with high resolution, the molecular motions responsible for the self-healing process.
It turns out that self-healing in these materials consists of several elementary processes, which include the flow of the polymer to fill the gap created by cutting through the material with a knife, adhesion of the separated parts of the solid, and the restoration of molecular bonds that had been broken by the action of the knife.
These results not only illuminate the complex cascade of steps involved in autonomous repair, which forms a stepping stone for developing even better self-healing materials in the future, but demonstrate how this novel method can shed light on such complex mechanical phenomena. In the present paper, the authors studied how induced damage can heal spontaneously, but the technique can do more. Hanne van der Kooij, the PhD student who carried out most of the work, says: “The same approach allows us to see how damage starts in the first place. How the breaking of a single molecular bond can set in motion a self-catalytic cascade that ultimately leads to macroscopic fracture”. Research in these groups is now also directed to unravel the molecular cascade of damage accumulation at the origin of fracture, delamination and wear.