Synergic thermal and light responsive self-healing smart coatings: A combination of dynamic transesterification reactions with azobenzene isomerization

This study introduces a novel self-healing vitrimer material (AZO-HEV) prepared by covalently incorporating azobenzene moieties into an hydroxyester vitrimer network (HEV) which was obtained by the reaction between epoxy groups with glutaric acid (GA), to enable both thermal and light-induced repair. Structural characterization, including size exclusion chromatography (SEC), swelling, Fourier transform infrared (FTIR) spectroscopy and UV–visible spectroscopy, confirmed the successful preparation of highly crosslinked networks and verified the covalent incorporation of 4-(phenylazo)phenol (AZO) into the polymer matrix with minimal free AZO remaining. Dynamic mechanical analysis (DMA) further showed that AZO-HEV relaxes significantly faster than HEV, indicating enhanced chain reconfiguration. Both materials, HEV and AZO-HEV, exhibit shape memory properties and thermal induced partial recovery upon relaxation. The functionalized material, AZO-HEV, demonstrated a dual-mechanism healing capability that surpassed the limitations of the parent HEV. While HEV could only achieve modest thermal recovery at high temperatures, AZO-HEV leveraged the azobenzene units' rapid cis-trans isomerization to induce long-range segmental mobility. This resulted in a 50% light-induced recovery and up to 65% thermal healing. AZO-HEV achieved its maximum recovery of 80% through the synergistic effect of light and moderate temperature (100 °C). It was determined that temperature is a decisive parameter, as excessive heat interferes with the light-healing mechanism, dramatically reducing recovery below 30%. The difference in damage response was also noted: AZO-HEV showed plastic deformation against the brittle fracture of HEV, indicating a fundamental shift in mechanical behavior. These findings confirm that the strategic integration of AZO enables a highly efficient, externally controlled self-healing system, capable of complex molecular-level spatial reconfiguration through light, heat, or a synergistic combination. • Azo groups are covalently attached efficiently to a hydroxyester vitrimer network. • Hydroxyester vitrimers with azo groups showed excellent repairability. • The incorporation of azo moieties provided light responsiveness to the vitrimers. • A synergic effect was observed by repairing azo-vitrimers with light and heat.