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.

Soft Fiber/Textile Actuators: From Design Strategies to Diverse Applications

“…(a) Schematic melt-extrusion spinning process of the fibers, (b) an image of melt-spun fiber. Reprinted with permission under a Creative Commons CC BY license from ref . Copyright 2023 The Authors.…”

“…83 As shown in Figure 6a, the thermoplastic LCE were heated to the melting temperature, followed by extruding through a capillary rheometer. 84 After cooling in the air for 2 min, the extruded fiber gradually solidify, and the fiber have a diameter of about 1.3 mm (Figure 6b). Qi et al fabricated a shape memory zinc dimethacrylate/ethylene vinyl acetate (ZDMA/EVA) composite fiber by melt spinning (Figure 6c).…”

“…Polymers for melt spinning should melt or become viscous without decomposing . As shown in Figure a, the thermoplastic LCE were heated to the melting temperature, followed by extruding through a capillary rheometer . After cooling in the air for 2 min, the extruded fiber gradually solidify, and the fiber have a diameter of about 1.3 mm (Figure b).…”

Free-Form Liquid Crystal Elastomers via Embedded 4D Printing

“…22 These large mechanical actuations result from nematic-toisotropic phase transitions, which cause rotation of the LCE polymer backbone, also known as mesogens. While LCE alignment strategies traditionally rely on mechanical stretching, 23,24 light, 9 or magnetic fields, 25 recent studies have explored the coupling of 3D printing processes and LCE alignment. 26,27 For example, during direct ink write (DIW) 3D printing, LCE mesogens are aligned by the shear forces exhibited on the LCE ink during extrusion through the DIW nozzle.…”

“…These large mechanical actuations result from nematic-to-isotropic phase transitions, which cause rotation of the LCE polymer backbone, also known as mesogens. While LCE alignment strategies traditionally rely on mechanical stretching, , light, or magnetic fields, recent studies have explored the coupling of 3D printing processes and LCE alignment. , For example, during direct ink write (DIW) 3D printing, LCE mesogens are aligned by the shear forces exhibited on the LCE ink during extrusion through the DIW nozzle. , This approach has enabled facile fabrication of a myriad of unique geometries, such as conical, lattice, or tensegrity structures for shape-changing assemblies. While DIW can be used for 4D printing of LCE-driven shape-changing structures, only planar 2D architectures can be generated, significantly limiting their applications to in-plane actuation or simple bending shape transformations.…”