Self healing supramolecular nanocomposites

We have designed, prepared, and characterized a class of advanced intrinsic self-healing polymer nanocomposites where the self-assembled filler skeleton formed by nanoparticles is embedded in a continuous phase of a supramolecular elastomer. In intrinsic self-healing systems the ability for a material to repair itself is achieved by keeping the required mobility in the system while using nanoparticle reinforcement to achieve the overall stiffness and resilience. This means that it is indeed possible to design a material that reconciles both mobility and stiffness, which at first sight might seem a tall order. Unlike self-healing materials based on encapsulated reagents, solvents or adhesives, the intrinsic self-healing mechanism is engrained into the material itself, and self-healing can be repeated indefinitely, also at previously damaged locations. The reinforcing skeleton that interpenetrates through the polymer matrix not only prevents the supramolecular elastomer matrix from flowing, but also provides the nanocomposite with load-bearing capabilities. The supramolecular polymer we discuss here is boric acid modified poly(dimethylsiloxane), PBS. During the PBS synthesis boric acid cleaves silicone oil chains (PDMS) forming hydrogen bonding boric acid end-groups. These end-groups can subsequently also form covalent crosslinks via reversible boroxol rings. The supramolecular PBS elastomer is responsible for integrating the two-component nanocomposite as a whole by means of its reversible intermolecular H-bonding cross-links. By fine tuning the nanoparticle-molecule adhesion, the particle aspect ratio, and the particle network formation, we are able to obtain a load-resistant nanocomposite without prolonging the healing time.