Melt-Extruded Thermoplastic Liquid Crystal Elastomer Rotating Fiber Actuators

Abstract

Untethered soft fiber actuators are advancing toward next-generation artificial muscles, with rotating polymer fibers allowing controlled rotational deformations and contractions accompanied by torque and longitudinal forces. Current approaches, however, are based either on non-recyclable and non-reprogrammable thermosets, exhibit rotational deformations and torques with inadequate actuation performance, or involve intricate multistep processing and photopolymerization impeding scalable fabrication and manufacturing of millimeter-thick fibers. Here, the melt-extrusion and drawing of a 50 m long thermoplastic liquid crystal elastomer fiber with a ≈1.3 mm diameter on a large scale is reported. With the responsive thermoplastic material, rotating actuators are fabricated via easily exploited programming freedom resulting in large, reversible rotational deformations and torques. The actuation performance of the twisted fibers may be controlled by the programmed twisting density without complicated preparation steps or photocuring being required. The thermoplastic behavior enables fabrication of plied fibers, demonstrated as a triple helical twisted rope constructed from individual rotating fibers delivering up to three times as great rotational and longitudinal forces capable of reversibly opening and lifting a screw cap vial. Besides the programmability, the thermoplastic material employed lends itself to be completely reprocessed into other configurations with self-healing properties in contrast to thermosets.