Electrical breakdown of an acrylic dielectric elastomer: Effects of hemispherical probing electrodes size and force

Dielectric elastomers are widely investigated as soft electromechanically active polymers (EAPs) for actuators, stretch/force sensors and mechanical energy harvesters to generate electricity. Although the performance of such devices is limited by the dielectric strength of the constitutive material, the electrical breakdown of soft elastomers for electromechanical transduction is still scarcely studied. Here we describe a custom-made setup to measure electrical breakdown of soft EAPs and we present data for a widely studied acrylic elastomer (VHB 4905 from 3M). The elastomer was electrically stimulated via a planar and a hemispherical metal electrode. The breakdown was characterised under different conditions to investigate the effects of the radius of curvature and applied force of the hemispherical electrode. With a given radius of curvature the breakdown field increased by about 50% for a nearly ten-fold increase of the applied mechanical stress, while with a given mechanical stress the breakdown field increased by about 20% for an approximately two-fold increase of the radius of curvature. These results indicate that the breakdown field is highly dependent on the boundary conditions, suggesting the need for reporting breakdown data always in close association with the measurement conditions. These findings might help future investigations to elucidate the ultimate breakdown mechanism/s of soft elastomers.