Spatially and Temporally Programmable Transparency Evolutions in Hydrogels Enabled by Metal Coordination toward Transient Anticounterfeiting.

Hydrogels have emerged as promising candidates for anticounterfeiting materials, owing to their unique stimulus-responsive capabilities. To improve the security of encrypted information, efforts are devoted to constructing transient anticounterfeiting hydrogels with a dynamic information display. However, current studies to design such hydrogel materials inevitably include sophisticated chemistry, complex preparation processes, and particular experimental setups. Herein, a facile strategy is proposed to realize the transient anticounterfeiting by constructing bivalent metal (M 2+ )-coordination complexes in poly(acrylic acid) gels, where the cloud temperature (T c ) of the gels can be feasibly tuned by M 2+ concentration. Therefore, the multi-T c parts in the gel can be locally programmed by leveraging the spatially selective diffusion of M 2+ with different concentrations. With the increase of temperature or the addition of a complexing agent, the transparency of the multi-T c parts in the gel spontaneously evolves in natural light, enabling the transient information anticounterfeiting process. This work has provided a new strategy and mechanism to fabricate advanced anticounterfeiting hydrogel materials.