Photoreactive nanoparticles as nanometric building blocks for the generation of self-healing hydrogel thin films

The use of reversible photo-cross-linkable nanoparticles as nano building blocks for the formulation of nanostructured self-healing thin hydrogel films is shown for the first time. This strategy for the fabrication of autonomous self-healing coatings consisted of various microgels bearing surface cinnamate moieties. The nanoparticles were formed by miniemulsion copolymerization, which was followed by surface functionalization with the cinnamate groups. These nanoparticles were then used to form films by drop-casting, followed by interparticle photo-cross-linking polymerization through the light-induced forward dimerization reaction of the previously incorporated cinnamate groups. The reversibility of this macroscopic network formation was also demonstrated by photoinducing the backward dimerization reaction and carrying out several cycles of photoinduced cross-linking and de-cross-linking. The self-healing ability through swelling of these films following surface damage was also demonstrated. Finally, the ability of these self-healing macroscopic films to incorporate additives of different chemical nature before photo-cross-linking was evaluated.