Self-healing supramolecular polymers

Materials are autonomously self-healing when repair is triggered not by external intervention (heat, light ...) but by the damage itself. Complex composite architectures have been devised by several groups to show essentially this type of behaviour. On the other hand, a simple polymer melt is repeatedly self-healing, by simple reentanglement of polymer chains. The problem is that even though at short time such a material behaves like an elastic solid, it has sticky surfaces and finally, at long times it flows under the effect of a constraint. Achieving a homogeneous polymer material that can behave like a real elastic solid and can self-repair without external action is therefore a challenge. Supramolecular chemistry teaches us to control non-covalent interactions between organic molecules, particularly through the use of optimized building blocks capable of establishing several hydrogen bonds in parallel. On this basis, we will discuss design principles and our endeavours to create novel supramolecular networks with rubbery elasticity, self-healing ability and as little as possible creep. Our strategy was to synthesize assemblies of randomly branched Hbonding oligomers rather than a single molecule. While our materials are non-sticky elastomers, they can be repaired in case of damage, even after a long waiting time, by simply bringing together fractured surfaces. To understand this paradox, we will show that not only the optimization of hydrogen bonding groups but also the self-assembling ability of the molecular unit as a whole are key parameters which control cohesion, organization and eventually the long lived nonequilibrium state that promotes the self-healing event.