Dual physically crosslinked azobenzene liquid crystal elastomers programmable for multi-modal information encryption

Abstract

Dynamic interactions endow liquid crystal elastomers (LCEs) with network rearrangeability, facilitating the fixation of mesogen alignment induced by external forces and enabling reversible actuation. Nevertheless, the need for high stability in the networks used to fix the orientation of liquid crystal (LC) remains an inherent problem limiting the development of LCEs. Herein, azobenzene liquid crystal elastomers (Azo-LCEs) with dual physical crosslinking from 2-ureido-4-pyrimidone (UPy) and glassy polystyrene (PS) are developed to address this issue. Unlike conventional systems, our UPy hydrogen bonds dissociation begins at temperatures below the LC-isotropic phase transition temperature (T_LC-iso), prompting the proposal of a novel mechanism for locking in LC orientation. The reversible UPy network exhibit continuous dynamic equilibrium under mild condition, enabling locking in LC actuation domains, where Azo mesogens align perpendicular to the stretching direction. By systematically investigating the dynamic mechanisms of UPy and structure–property relationships, the thermomechanical, photochromic and photomechanical behaviors are optimized. These Azo-LCEs exhibit thermo-induced anomalous reversible deformation, erasable photolithography imaging and photo-programmable deformations. To showcase multifunctionality, we designed an information system using patterned Morse code masks, enabling encryption and decryption through thermo-induced anomalous actuation. Combining heating with photo-programing parameters, the pre-stored deformation can be decrypted into different meanings for multidimensional information encryption. A movable-type information encryption system is achieved by cooperating water-assisted UPy self-healing and Azo erasable photolithography imaging. Exploiting the synergistic interplay of photochromic and photomechanical properties, we developed a snap-ring wristband-like device capable of dynamically displaying and concealing information. Producing the effect of 1 + 1 > 2, this work highlights the synergistic potential of multifunctional materials and innovative processing strategies, offering multiple information encryption modes and advancing the design of intelligent materials.