Long-chain crosslinker-induced patterning on an elastic polymer film for robust and reversible information encryption/decryption

While reversible information encryption and decryption are readily achievable with hydrogels, this process presents a significant challenge when applied to elastic polymer films. This is due to the inherent chemical stability of anhydrous polymer films which significantly increases the difficulty of information writing. In this study, we propose a solvent-free radical polymerization method for chemical patterning on the elastic film of poly(styrene-butadiene-styrene) (SBS). Unlike short chain crosslinkers-induced patterning, which increases the brittleness of the film, the long-chain crosslinkers are chemically bonded with the chains of SBS. This not only enhances the mechanical stability of film, but also improves its softness and robustness (the strength increases 1.8 times and the toughness increases 2.3 times), thereby greatly extending its durability for information encryption and decryption. When patterned with a photomask, the crosslinked regions maintain transparency upon acetone absorption, while the non-crosslinked regions become opaque due to an acetone-induced phase change. Upon removal of acetone, these opaque regions can be restored to transparency. Compared with hydrogels liable to water loss and deformation, the patterned films show greater stability, retaining pattern encryption/decryption functions after 30 days in a natural environment without special storage. The rate of this phase transition is directly related to the degree of crosslinking. Therefore, by adjusting the degree of crosslinking, the patterned films can undergo multistage encryption/decryption in response to acetone, providing a promising method for information security and storage.