Thermal- and photo-responsive liquid crystalline elastomers fabricated using tung oil-based azobenzene

Abstract

Azobenzene-based liquid crystalline elastomers with dynamic ester bonds exhibit high thermal- and photo-responsive properties. However, there are a few studies that focus on photo-induced and thermal-induced behaviors separately. Herein, novel thermal- and photo-responsive LCEs containing dynamic ester bonds were prepared from 4,4’-diglycidyloxy-azobenzene, sebacic acid and tung oil-based azobenzene, which acted as a side chain. The dynamic transesterification reactions on the network structure were confirmed through stress relaxation. The photo-induced and thermal-induced behaviors were also investigated. The monodomain LCEs film was obtained by uniaxial stretching at a temperature above the smectic–isotropic phase transition temperature (Ti ∼82 °C). Due to the breakage and formation of dynamic ester bonds and the order-disorder smectic phase transition caused by heat and the trans-cis isomerization of azobenzene mesogens, the thermal-induced stress of the monodomain LCEs film reached ∼3 MPa. The LCEs film also exhibited thermal-induced shape-memory properties. Investigation of its photo-responsive behavior further demonstrated that the monodomain LCEs film generated stress of ∼1.1 MPa while exhibited photo-induced deformation due to the trans-cis isomerization of azobenzene mesogens upon irradiation with 365 nm UV light. Finally, we observed that the monodomain LCEs film could undergo quickly photo-induced deformation and could be processed into a photo-driven gripper.