Investigation into the electromechanical properties of dielectric elastomers subjected to pre-stressing

• Pre-stretch greatly affected electromechanical properties of DEs in this work.
• Silicone based DE achieved an area strain of 32% at the pre-stretch ratio of 1.6.
• Pull-in instability was absent on SR and appeared on VHB 4910.

Dielectric elastomers (DEs) are being exploited for biological applications such as artificial blood pumps, biomimetic grippers and biomimetic robots. Generally, polyacrylate and silicone rubber (SR) are the most widely used materials for fabricating DEs in terms of mixing with other polymers or compounding them with highly dielectric particles. Furthermore, pre-stretch offers an effective approach to increasing actuated strain and dielectric strength and eliminating ‘pull-in’ instability. In the work described here, a comparison in electromechanical properties was made between SR/10% barium titanate (BaTiO3) and commercial VHB 4910. Trends in these dielectric parameters are shown graphically for variation in pre-stretch ratio (λpre). It was found that permittivity of SR/10% BaTiO3 was independent of frequency, whereas permittivity was frequency-independent due to the polarization of polymer chains. The maximum deformation and the coupling efficiency for SR/10% BaTiO3 can be achieved at a pre-stretch ratio between 1.6 and 1.9. For VHB 4910, they can be obtained in the pre-stretch ratio range from 2.6 to 3.0. A maximum energy density of 0.05 MJ/m3 was achieved by SR/10% BaTiO3 (λpre = 1.6) and VHB 4910 (λpre = 3.4). The findings provide an insight into critical pre-stretch ratios required for a range of applications of DEs based on silicone and the commercially available polyacrylate VHB 4910.

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