Three birds with one stone: Design and synthesis of polyurethane actuator for executing heat, light and humidity triggered deformation

Intelligent actuation materials are widely utilized as parts of soft robots, smart sensors and other applications, due to their response to external stimuli (such as heat, light, magnetism, humidity, etc.). Yet preparing a single polymer material with multi-stimuli responsive functions remains challenging and less explored. Herein, we have explored a novel multi-stimuli responsive intelligent actuating polyurethane material, AzoPU50, through one-pot co-polymerization of 4,4′-bis (6-hydroxy-hexoxy) azobenzene (BHHAB), polyethylene glycol 400 (PEG400) and 4,4′-methylene bis (phenyl isocyanate) (MDI) at a ratio of 1:1:2. This novel material can respond to three types of stimuli to trigger shape deformation movements. The intrinsic microphase separation structure of polyurethane can afford thermal responsive shape memory performances. Furthermore, the variation in the configuration of azobenzene units endows the polyurethane film with good light-responsive deformation. Most importantly, this polyurethane actuator can also achieve humidity-responsive movements including flipping motion on a wet filter paper, bending deformation driven by the palm and finger, etc. In addition, a biomimetic device that integrated the heat, light and humidity stimuli together to imitate human gestures of praise was successfully assembled. This work provides a new strategy for constructing actuators with triple-functions and will pave a way for further development of multi-stimuli-responsive smart actuating devices and other intelligent materials/systems.