Self-healing hybrids fabricated by metal complexation with imidazole-containing silsesquioxane nanoparticles

Abstract

Simultaneous achievement of self-healing ability and material hardness in materials is challenging because these properties are contradictory. In this study, we designed self-healable hybrids based on organic–inorganic silsesquioxane nanoparticles (SQ-NPs) having imidazole and n-alkyl groups in a single arm. The imidazole moiety acted as a self-healing motif via dynamic metal–ligand (zinc–imidazole) interactions while the n-alkyl functional groups act as a flexible unit to manipulate the chain mobility. Three imidazole-containing SQ-NPs having different n-alkyl chains were prepared by thiol–epoxy click reaction followed by esterification. X-ray diffraction, scanning force microscopy, thermogravimetric analysis, and differential scanning calorimetry measurements revealed the formation of SQ-NPs (< 5 nm) with relatively narrow size distributions and no aggregation and manipulated thermal properties. The zinc/imidazole-based hybrids prepared by the complexation of the imidazole-containing SQ-NPs with ZnCl₂ exhibited a high degree of tunability (Young's modulus in the range of 0.56–2.13 GPa) with good self-healing efficacy (recovered 80% of inherent mechanical properties at 50 °C for 24 h), which was attributable to the healing nature of the rapid exchange of zinc–imidazole interactions, in addition to amorphous SQ-NP mobility.