Ultra-High Actuation Stress Polymer Actuators as Light-Driven Artificial Muscles

Remotely addressable actuators are of great interest in fields like microrobotics and smart textiles because of their simplicity, integrity, flexibility, and lightweight. However, most of the existing actuator systems are composed of complex assemblies and/or offer a low response rate. Here, the actuation performance of a light-driven, highly oriented film based on ultra-high molecular weight polyethylene (UHMW-PE), containing a photo-responsive additive, 2-(2H-benzotriazol-2-yl)-4,6-ditertpentylphenol (BZT), is reported. The material exhibits a fast (<1 s) and reversible photo-induced thermal response upon exposure to UV light, which results in an exceptionally high actuation stress (∼70 MPa) at a low strain (<0.1%). The proposed actuation mechanism originates from light absorption by BZT and energy transfer into heat, in combination with the intrinsic high stiffness (∼80 GPa) and a negative thermal expansion (NTE) of the oriented polymer films. This unique set of properties of this actuator, in particular the very high specific actuation stress, compared to existing organic and inorganic actuators, and the remote optical actuation, promises impact in fields related to soft robotics, composites, medical devices, optics, prosthetics, and smart textiles.