Multi-responsive P(DMAEMA-co-COU) hydrogel for temperature sensor and information encryption

Multi-responsive hydrogels for temperature sensor and information encryption were developed through the synergistic application of light, temperature and pH response of the hydrogel. The multi-responsive hydrogels were prepared by copolymerization of dimethylaminoethyl methacrylate (DMAEMA) and 7-(2-methacryloyloxyethoxy)-4-methylcoumarin (CoumMAc). Through incorporating coumarin groups into the hydrogels, the crosslinking degree of hydrogels could be increased by photo-crosslinking of polymer chains based on the photodimerization of coumarin groups. After the hydrogel was irradiated by a photomask under UV light (365 nm), the irradiated and unirradiated region in the hydrogel showed different crosslinking degrees, leading to different volume phase transition temperature (VPTT) in the two region of the hydrogel. The pattern in the hydrogel appeared only within a specific temperature range, and the temperature of the environment can be monitored by the prepared hydrogel sensor. After soaking the patterned hydrogel in the acidic solution, no pattern information was displayed at all temperatures, and the pattern information can only emerge by dual decryption (base and temperature). In addition, the information can be erased by UV light (254 nm), which further ensures information security. This work provide a new way for low-cost unpowered temperature sensors and information encryption with more security.