Magnetic Structural Color Hydrogels for Patterned Photonic Crystals and Dynamic Camouflage

The development of programmable structural color hydrogels that can adapt to the variation of surrounding environments is of paramount importance for many important applications such as biosensing, information encryption, advanced anticounterfeiting, and adaptive camouflage. Herein, we report the design and fabrication of magnetic structural color hydrogels by introducing superparamagnetic core-shell Fe3O4@poly(4-styrenesulfonic acid-co-maleic acid) (PSSMA)@SiO2 nanoparticles into acrylamide and polyethylene glycol diacrylate hydrogels. The colloidal magnetic nanoparticles (MNPs) were able to self-organize into photonic crystals (PCs) under an external magnetic field, so that a variety of tunable structural color hydrogel patterns could be developed via magnetically induced self-assembly of colloidal MNPs and a subsequent mask-assisted UV polymerization of the pregel solution. Interestingly, the resulting hydrogels and PC patterns could swell in water, and the swelled hydrogels were able to shrink upon light irradiations, which resulted in the dynamic and reversible modulation of the structural color. As a proof-of-concept application, a chameleon-like structural color hydrogel was fabricated, and dynamic camouflage was demonstrated upon cyclic exposure to water and light irradiations. The research disclosed herein could shine a light on the development of advanced intelligent structural color hydrogels for diverse applications such as camouflage, anticounterfeiting, and beyond.