Visualizing polymer diffusion in hydrogel self-healing

Abstract

Self-healing hydrogels are attractive to extend material lifetime by rapid recovery from damage; the underlying healing mechanism regarding polymer diffusion are of broad research interest. However, intuitive and convenient characterization of polymer diffusion remains challenging due to the complex and dynamic features of hydrogels. Herein, we have constructed a dually-crosslinked hydrogel system to decouple complex factors for direct visualization of polymer diffusion and quantified study of healing dynamics. The successively formed dually-crosslinked hydrogel networks are designated for purposes of self-healing/visualization and tunable constraining effects (varied crosslinking density), respectively. As a result, we observed direct polymer diffusion across the crack interface and calculated the diffusion speed ranging from 0.51 to 0.04 μm/s depending on varied constraining degree. The corresponding self-healing performance is consistent with other conventional characterizations (e.g., dynamic mechanical properties, surface morphology changes). The above method has enabled facile visualization of dynamic healing processes with flexible adjustment of polymeric systems, which could inspire novel designs of high-performance self-healing materials.