Surface engineering of nanosilica for vitrimer composites

Vitrimers are a new kind of crosslinked polymers with attractive properties of repairing and reprocessing. It is very important to further improve the physical properties of vitrimers to meet the ever growing demand for high-performance materials. However, the mechanical reinforcement of vitrimer matrix by nanoparticles was always accompanied with hindered topological rearrangement because of the restricted chain mobility. In this paper, epoxy and thiol groups functionalized silica nanoparticles (EP-Silica and SH-Silica) were used as fillers for construction of disulfide based vitrimer composites to investigate the surface chemistry of nanoparticles on mechanical and adaptive properties of vitrimers. It is found that both EP-Silica and SH-Silica showed good mechanical reinforcement because of the covalent bonding with matrix as compared to unmodified silica. Although the mechanical reinforcement of SH-Silica was slightly inferior to that of EP-Silica, the stress relaxation of composite reinforced by SH-Silica was much faster than that of EP-Silica filled composite. As a result, SH-Silica based composite showed higher self-healing efficiency as evidenced by time dependent healing tests. Further improvement in mechanical property of composite with moderately retarded stress relaxation at high loading of SH-Silica was also demonstrated. This work demonstrated the possibility of tuning the mechanical and adaptive properties of vitrimer composites by surface engineering of nanoparticles.