Low-temperature reprogrammable dual light-responsive liquid crystalline elastomer films

The liquid crystal elastomers (LCEs) possessing azobenzene moieties and boron ester bonds were prepared using Michael addition reaction and photopolymerisation. The azobenzene moieties imparted the LCEs with photoresponsiveness, whereas the boron ester bonds enabled the LCEs to undergo director alignment, reprogramming, and self-healing through a dynamic bond exchange reaction (DBER). This combined strategy overcame the competition between actuation and a DBER at high temperatures, which has been a drawback in the previously developed LCE vitrimers. Interestingly, the developed monodomain LCEs (MLCEs) showed the bending actuation in responsive to both UV and blue lights and unbending motion in responsive to green light, which paves the way for the design of new actuators for biomedical applications. Furthermore, taking advantage of the dynamic nature of boron ester chemistry, bilayer-structured actuators capable of thermo- or photo-controllable bending/ unbending motions were fabricated by welding the MLCE film with a poly(ethylene terephthalate) substrate or itself below their nematic-to-isotropic transition temperatures via a 'glue-free' method. The MLCEs developed in this study can undergo multidirectional movements in response to different stimuli and can be used in applications such as microrobots, untethered biomimetic grippers, and surgical instruments.