Dielectric elastomer actuators (DEAs) are a class of electrostatic actuators that have promising applications in fields like sensors, soft-robotics, microfluidics, and energy harvesting. The crucial points in the working principle of DEA are the application of high electric field and the use of compliant electrodes. These electrodes are typically composed of a mixture of a soft polymer base filled with highly conductive particles. In this work, we show that the charged impurities, possibly present in the electrodes composite, in combination with a high electric field can cause the formation of polarization interface layers between the electrodes and the inner dielectric. These layers can, in the long term, diminish the actuation performance of the DEA.

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Pre-stretching membranes in dielectric elastomer actuator (DEA) systems is a widely known technique to improve the dielectric’s breakdown strength and therefore enhance the overall device performance. The impact of this approach on the long-term reliability of DEAs is, however, still unknown. In the present work, it is investigated how the elastomer lifetime is affected by the mechanical pre-stretch. Silicone membrane samples with different pre-stretch ratios were prepared and the respective DC dielectric strengths were measured for both short and prolonged tests using methodologies inherited from high voltage assessment technology. It is shown that, despite an absolute beneficial increase of the dielectric strength for the tensioned membranes, pre-stretching has a detrimental effect on the system’s useful life. In all the studied cases, the pre-stretched specimens showed a shorter expected lifetime compared to new, relaxed membranes. The results suggest a careful selection of the relative electric field to be applied to DEAs system for long and reliable lifetime.@en

Soft insulators are the main component used in dielectric elastomer actuators (DEAs). It follows that dielectric properties like permittivity and dielectric strength of the insulator can strongly influence the maximum dynamic actuation performance of DEA devices. We observed an increasing breakdown voltage with increasing driving AC voltage frequency for silicone-based dielectric films. Despite the breakdown voltage increase, we demonstrate that there is no actual breakdown electric field rise with varying frequencies. We show that the voltage behavior is rather compatible with a constant dielectric breakdown field model and the slow mechanical response of the elastomer.@en

Dielectric elastomers (DE) have lately drawn attention for their use in soft actuators and electromechanical energy harvester. Excellent dielectric properties and high mechanical deforming capability are key requirements of DEs. Given that the output strain of DE system is proportional to the applied electric field squared (and vice versa), - high electric field is needed to generate large displacement. Similarly to any other insulation exposed to high electric field, DEs undergo electrical ageing. Furthermore, DEs undergo continuous mechanical deformation during its lifetime. Therefore, the lifetime of DE system can be shortened by the simultaneous action of electric and dynamical mechanical stress. This can lead to a faster overall ageing of DE system with respect to other common HV devices, that usually are mechanically-static. To extend the useful life of the system it is firstly important to know how fast the electromechanical degradation process is and what is the contribution of electrical and mechanical stresses. Secondly, assess its ageing stage and adjust its output accordingly, albeit with a lower effectiveness. Partial discharge testing has been used to assess the health of a silicon polymer elastomer typically used in dielectric elastomer generator. The mechanical ageing of a DE system has been qualitatively evaluated by monitor PD activity over different cycles of usage and reported in this paper.

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Film pre-stretching is a widely adopted solution to improve dielectric strength of the DEA systems. However, to date, long term reliability of this solution has not been investigated. In this work it is explored how the dielectric elastomer lifetime is affected by film pre-stretching. The dielectric loss of soft polydimethylsiloxane (PDMS) films is studied for different stretch ratios by measuring tanδ. Additionally, time-to-breakdown was measured at DC electric stress for different stretch ratios. For this purpose, accelerated life test (ALT) were performed. The results obtained are compared with non-pre-stretched samples. This study suggests that no additional dielectric losses are caused by film stretching up to 80% of original dimensions. @en