Self‐Strengthening Dielectric Elastomer of Triblock Copolymer with Significantly Improved Electromechanical Performance under Low Voltage

Abstract Dielectric elastomer actuators (DEAs) are promising soft electromechanical transducers for soft robotics. Fabricating a high‐performance DEA actuated by sub‐kV voltage remains challenging. Here, a facile method not only to fabricate ultrathin dielectric elastomer films of triblock copolymers but also to enhance the dielectric breakdown strength and thus enhance the electromechanical performance is reported. A thick thermoplastic elastomer film of poly(styrene‐ b ‐butyl acrylate‐ b ‐styrene) from solution blading is symmetrically pre‐stretched and relaxed at 120 °C to fabricate a freestanding ultrathin DE film. Compared with the pristine DE film of the same thickness (12 µm), the thermally‐relaxed DE film with equally biaxial pre‐stretch ratio 3.5 × 3.5 exhibits increased electrical breakdown strength by a factor of 1.9 (from 43 to 82 V µm −1 ), maximum actuation area strain by a factor of 1.9 (from 11.7% to 22.4%), and highest energy density by a factor of 5.7 (from 4.5 to 25.8 kJ m −3 ). The enhancement may be ascribed to the self‐reinforcement of the dielectric breakdown strength due to the morphology change of polystyrene nanodomains from spheres to oblate spheroids. Thanks to the ultra‐thinness, the high electromechanical performance is achieved within sub‐kV driving voltage in all cases.