Preparation and properties of azobenzene liquid crystal networks with stable and reversible deformation, self-healing characteristics

Abstract

Photo-responsive liquid crystal networks (LCNs) can respond to optical stimuli and show significant macroscopic reversible deformation, which is promising for applications in flexible actuators, artificial muscles, and other fields. To date, most of the photo-responsive LCNs have been constructed using azobenzene as photo-responsive group. However, how to prepare azobenzene-LCNs (azo-LCNs) with stable deformation remains a challenge. In this article, we provide a new strategy for preparing azo-LCNs with stable and reversible deformation. We copolymerize azobenzene monomer M6AZ1, commercially butyl acrylate monomer BA, and dynamic covalent cross-linker monomer M6HABI to obtain azo-LCNs. When irradiated with 365 nm light, the uniaxially oriented LCN fibers undergo bending towards light due to the photo-isomerization of azobenzene, and the bending angle increases with azobenzene component content in LCNs. With the highly reversible process of dynamic C–N bonds dissociation-reconjugation, the rearrangement and regeneration of covalent crosslinked network can be realized. Hence, the newly formed cross-linked network locks the deformation of azo-LCNs, and this deformation can be maintained for more than 90 days. When heated, the deformation can return to the original state. In addition, the LCNs also exhibit self-healing and reprocessing properties.