Abstract
Phase-change material–elastomer composite (PCMEC) actuators are composed of a soft elastomer matrix embedding a phase-change fluid, typically ethanol, in microbubbles. When increasing the temperature, the phase change in each bubble induces a macroscopic expansion of the matrix. This class of actuators is promising for soft robotic applications because of their high energy density and actuation strain, and their low cost and easy manufacturing. However, several limitations must be addressed, such as the high actuation temperature and slow actuation speed. Moreover, the lack of a consistent design approach limits the possibility to build PCMEC-based soft robots able to achieve complex tasks. In this work, a new approach to manufacture PCMEC actuators with different fluid–elastomer combinations without altering the quality of the samples is proposed. The influence of the phase-change fluid and the elastomer on free elongation and bending is investigated. We demonstrate that choosing an appropriate fluid increases the actuation strain and speed, and decreases the actuation temperature compared with ethanol, allowing PCMECs to be used in close contact with the human body. Similarly, by using different elastomer materials, the actuator stiffness can be modified, and the experimental results showed that the curvature is roughly proportional to the inverse of Young’s modulus of the pure matrix. To demonstrate the potential of the optimized PCMECs, a kirigami-inspired voxel-based design approach is proposed. PCMEC cubes are molded and reinforced externally by paper. Cuts in the paper induce anisotropy into the structure. Elementary voxels deforming according to the basic kinematics (bending, torsion, elongation, compression and shear) are presented. The combination of these voxels into modular and reconfigurable structures could open new possibilities towards the design of flexible robots able to perform complex tasks.
Highlights
Active soft matter has gained increased interest for the fabrication of robotic devices with a large range of applications
It can be understood that the actuation stress generated by the microbubble expansion will result in a strain, and a curvature, inversely proportional to the matrix stiffness: k ∼ ε ∼ E1. Such best-fitting curves are represented on the figure, and the experimental results follow roughly the expected dependency
We demonstrated that choosing an appropriate phase-change fluid increases the actuation strain and speed, while decreasing the actuation temperature compared with ethanol
Summary
Active soft matter has gained increased interest for the fabrication of robotic devices with a large range of applications. Dielectric elastomer actuators are composed of an elastomer layer sandwiched between two electrodes, and can undergo shape deformation when subjected to an electric field, and can be used as artificial muscles and for various soft robotic applications (Gupta et al, 2019) Another interesting class of transducer relies directly on the thermal expansion of polymeric materials. Swelling or drying transducers rely on the fluid absorption of a matrix (Koetting et al, 2015), and allow the generation of high strains and use with a large range of material stiffnesses and dimensions Their chemically triggered actuation remains slow (Decroly et al, 2020)
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