Reprogrammable Solvent-Responsive Photonic Crystals via Reversible Ion Storage and Release toward Self-Erasable Steganography

Steganography based on responsive chromatic materials (RCMs) has attracted increasing interest in information encryption and anticounterfeiting. However, conventional RCMs suffer from immutable written states that can be read repeatedly, compromising the security. Herein, a self-erasable steganography method is developed by creating a reprogrammable solvent-responsive photonic crystal (RSPC), whose core mechanism depends on reversible Na + ion storage and release in gel networks. The RSPC is constructed by filling poly(di(ethylene glycol) ethyl ether acrylate) (PeDEGA) gels into an opaline template built by ZnS@SiO2 nanospheres. The selective infiltration and removal of NaOH aqueous solution or deionized water can manipulate the hydrophilic property of the RSPC, based on the partial hydrolysis of ester groups in PeDEGA and the subsequent conversion between acrylate sodium and acrylic acid. By controlling the solvent treatment sequence and area of the RSPC, a cycle of "write-hide-read-self-erase" has been realized for achieving the integration of self-erasability and steganography. The developed self-erasable steganography can enable written information to be read only once, which greatly enhances the security of the information. Meanwhile, this cycle also endows the RSPC with recycling ability and enhances its economy. Thus, this self-erasable steganography shows tremendous potential in the next-generation anticounterfeiting technology.