Actuator Materials for Environmentally Powered Engines

• Published in: Advanced materials technologies 2023-07, Vol.8 (13), p.n/a
• Main Authors: Spinks, Geoffrey M., Abbasi, Burhan B. A., Gautam, Aashrit, Mokhtari, Fatemeh, Jiang, Zhen
• Format: Article
• Language: English
• Subjects: actuators; artificial muscles; engines; shape memory alloys; twisted and coiled polymers
• ISSN: 2365-709X; 2365-709X
• DOI: 10.1002/admt.202202101

The first solid‐state engine that converted heat into continuous mechanical motion using a thermally responsive actuating material was introduced almost a century ago. These engines used vulcanized rubber where the cyclically heating and cooling of the rubber generate continuous mechanical power in pendulum or wheel type engines. The development of solid‐state heat engines has seen several waves of activity with interest stimulated by the introduction of new actuating materials capable of responding to different environmental stimuli. Opportunities for improved engine outputs are afforded by recently developed artificial muscle materials. A theoretical connection between engine output and the characteristics of the actuator material is developed to compare the performances of vulcanized rubber, shape memory alloys (SMAs), and twisted and coiled polymer (TCP) fiber artificial muscles. It is shown that with an engine designed to suit the actuation performance of TCPs engines powered by the tensile actuation of such materials would exceed the output of SMA heat engines. The properties needed in actuator materials to further enhance engine output are identified and polymer structures that may produce such properties are described. Engines that harness environmental energy, such as waste heat, can be powered by reversible length changes in actuating materials. Historically, vulcanized rubber and shape memory alloys have been employed in such solid‐state heat engines, but new materials are now emerging as superior alternatives. Matching the actuation behavior to engine design is critical to ensuring maximum engine work and power outputs.