Lower temperature and solvent dual response induced reversible information encryption and decryption hydrogels with host–guest recognition regulation

Abstract

It is a great challenge to develop information processing materials with powerful encryption/decryption functions because of the constraints of traditional materials. In this work, adamantane (Ad) groups were grafted onto poly (N-isopropyl acrylamide) (PNIPAm) to synthesize the PNIPAm derivative (Ad-PNIPAm) by radical polymerization, which was further used to fabricate the semi-interpenetrating network (IPN) composite hydrogel (Ad-PNIPAm gel) that exhibited dual temperature and solvent response optically tunable behavior under the assisted polymerization of NIPAM and chemical crosslinking of N,N′-methylene diacrylamide (MBA). The resultant composite hydrogel exhibited sensitive solvent and temperature stimulus response, high resolution and inducible reversible information recording, self-encryption and decryption functions. By changing the grafting degree of Ad-MA in Ad-PNIPAm, the hydrophilic–hydrophobic balance of Ad-PNIPAm could be adjusted to regulate the stimulus response of the Ad-PNIPAm gel. As the grafting degree of Ad groups increased, the response temperature of the Ad-PNIPAm gel gradually decreased, while the solvent response sensitivity was enhanced successively. In addition, this work not only controlled the encryption and decryption process of composite hydrogels by exploring different concentrations of ethanol solutions and various organic solvents, but also extended the information confidentiality time to the maximum extent and regulated the encryption and decryption process by introducing the host–guest recognition effects of β-cyclodextrin (β-CD) and Ad. Compared with the traditional PNIPAm hydrogel, the fabricated composite hydrogel possessed a wider temperature response range and a higher solvent response threshold, which could realize information entry, encryption and decryption at low temperatures, making the PNIPAm hydrogel based information processing model more suitable for real life scenarios. This PNIPAm based composite hydrogel with multiple regulation and multiple responses exhibited great potential in the fields of information writing and encryption/decryption.