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Actuator materials that can reproduce the multifunctionality of natural muscles have long been desired for the development of biologically inspired robots. Electroactive polymers (EAPs) have attracted increasing attention as potential candidates for artificial muscles. While several types of EAPs have been investigated, [1][2][3][4] electroelastomers, also known as dielectric elastomers, have been particularly attractive for largestrain and high-power applications. [5][6][7] Electroelastomers based on acrylic copolymer elastomers (e.g., 3M VHB 4910) and compliant electrodes have been shown to exhibit electromechanical strains of up to 380 % in terms of area expansion. Furthermore, the specific elastic energy density (3.4 J g -1), stress (up to 8 MPa), and electromechanical conversion efficiency (60-90 %) are all extraordinarily high. However, this outstanding performance is only observed when the acrylic films are highly prestrained. The reported specific elastic-energy density and stress are calculated from the weight or volume of the active acrylic elastomers. The performance of the packaged actuators is substantially lower.A number of actuator configurations, such as bow, bowtie, rigid-frame, diaphragm, and spring-roll actuators, have been designed to support the required high prestrain. [8,9] Each of these designs has its own unique advantages for certain applications, but without exception, the prestrain-supporting structures occupy significantly more space and weigh significantly more than the films themselves. The consequence of this is that the supporting structures cause a large performance gap between the active material and the packaged actuators. In addition, the lifetimes of the actuators are limited by the concentration of stress at the interfaces between the soft polymer film and the rigid supporting structure. The shock tolerance of the actuators is also reduced because of the introduction of rigid structural components. The prestrained films exhibit stress relaxation that affects the subsequent actuation.[10]Therefore, it would be highly desirable to eliminate mechanical prestraining while still retaining its performance benefits. We report here the development of new electroelastomers that exhibit high strain without requiring high prestrain. Electrically induced strain is proportional to the square of the applied electric field. High strain necessitates high breakdown strength. Prestrain enhances the dielectric-breakdown field of the elastomer films.[11] Mechanistic reasons for the enhancement of dielectric strength via mechanical prestraining are not well understood; we attribute it to the increased probability of hot electrons colliding with polymer chains realigned in parallel to the film surfaces. The prestrain also realigns defects, such as fibrous impurities, non-spherical voids, and gel particles, which may be responsible for premature dielectric breakdown. Here, we describe new interpenetrating elastomeric networks in which the benefits resulting from prestrain are obtained without exte...

Electroelastomers (electroactive elastomers) such as the 3M VHB 4910 acrylic adhesive films have exhibited up to 380% strain in area expansion at 5–6 kV when they are highly prestrained. By rolling highly prestrained electroelastomer films around a compression spring, we have demonstrated multifunctional electroelastomer rolls (MERs, or spring rolls) that combine load bearing, actuation, and sensing functions. We extended the design to two-degree-of-freedom (2-DOF) and 3-DOF spring rolls by patterning the electrodes to align radially on two and four circumferential spans of the rolls, respectively. Multiple-DOF spring rolls retain the linear actuation of 1-DOF spring rolls with additional bending actuation. Mathematical equations are derived to correlate the bending angle and lateral force of the rolls with the actuated stroke in one of the electroded spans. Two-DOF spring rolls with a 1.4 cm outside diameter, 6.8 cm axial length, and 11 g weight have been fabricated; these rolls have a 90° maximum actuation bending angle, 0.7 N maximum lateral force, and up to 15 N blocked axial force. Three-DOF spring rolls with a 2.3 cm outside diameter, 9.0 cm axial length, and 29 g weight exhibit a 35° maximum bending angle and 1.0 N maximum lateral force. These specifications can be modified by variations in roll parameters according to the equations. Multi-DOF spring rolls are easy to fabricate, compact, multifunctional, and mechanically robust. They represent a radically new actuation technology and may enable a number of unique applications. We have demonstrated a small walking robot, MERbot, with one 2-DOF spring roll as each of its six legs. The robot’s speed is as high as 13.6 cm s−1 or two-thirds of its length per second. ‘Sushi rolls’ have also been fabricated: these consist of six 2-DOF springs connected in series and monolithic in structure. The sushi rolls can be driven so as to generate wavelike or serpentine motion.

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