Paper of the week: Healable supramolecular polymer nanocomposite films

Healable polymeric materials have received increasing interest in recent years with the ultimate aim of improving the resilience of safety-critical components. Two distinct classes of materials have been developed – autonomously healing systems that repair in response to the fracture damage itself and healable materials that require an external intervention to promote healing. One of the major deficiencies of many supramolecular materials is that, in order to achieve healing at accessible temperatures and within usable timeframes, the materials are frequently elastomeric in nature with glass transition temperature well below ambient. These properties preclude the use of most supramolecular materials as structural components in high-value engineering applications such as in the aerospace industry.

Graphical abstract: Molecular recognition between functionalized gold nanoparticles and healable, supramolecular polymer blends – a route to property enhancement

Inspired by the success of polymer-composite materials in replacing metals across a range of high value products, Hayes and co-workers have investigated the possibility of producing nanoparticle-reinforced, supramolecular, healable composites. The material comprises a blend of three components: a pyrene-functionalized polyamide, a polydiimide and pyrene-functionalized gold nanoparticles (P-AuNPs). The polymeric components interact by forming well-defined π–π stacked complexes between π-electron rich pyrenyl residues and π-electron deficient polydiimide residues. Complexation studies in solution demonstrate that the introduction of P-AuNPs results in more rapid formation of an insoluble supramolecular network when compared to control samples that did not contain the P-AuNPs. Films of the nanocomposite are tough and flexible, and contain a relatively homogeneous dispersion of P-AuNPs. Films containing P-AuNPs are stronger and stiffer than those cast from the same polymers but without P-AuNPs, and also than films containing AuNPs that lacked the pyrenyl motif. Healing studies using a classic break/heal test, followed by stress–strain analysis, showed that materials containing up to 10 wt% P-AuNPs can even exhibit healing efficiencies of more than 100%.

Molecular recognition between functionalized gold nanoparticles and healable, supramolecular polymer blends – a route to property enhancement by Rajendran Vaiyapuri, Barnaby W. Greenland, Howard M. Colquhoun, Joanne M. Elliott and Wayne Hayes, Polym. Chem. 2013, 4, 4902-4909.

Julien Nicolas is a guest web-writer and advisory board member for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher.

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