Tannic acid/clay hydrogel with time-dependent mechanical and adhesive performance enabled by molecular interaction evolution

The investigation on dynamic molecular mechanisms is of importance for developing smart materials for various applications. Herein, we report a dynamic tannic acid (TA)/clay hydrogel with time-dependent mechanical and adhesive performance, in which clay plays an important role in regulating the molecular interaction evolution of hydrogels. Specifically, TA mediated the assembly of clay to form networked hydrogels driven by TA-clay dynamic interactions. Afterwards, clay served as a pro-oxidant component accelerated covalent crosslinking reactions of TA. Consequentially, the hydrogel transitioned from reversible dynamic networks to irreversible covalent networks over the time. Owing to the molecular interaction evolution, storage modulus of hydrogels gradually increased from 22 Pa to 3235 Pa in 4 days. Adhesive strength between hydrogels and iron substrates increased from 3 MPa to 23 MPa in 12 h and then decreased to 5 MPa. This finding will be a general principle for designing dynamic materials with time-dependent physicochemical properties and will enable various applications such as customized temporary adhesives.