Beware of your electrodes! How electrode materials and application processes impact the lifetime of slide-ring-material-based DEAs

For dielectric elastomer actuators (DEAs) to find more widespread adoption in commercial products, a better understanding of their durability is needed. By determining the different mechanisms contributing to ageing and breakdown in DEAs, new methods for improving their lifetime could be devised. Using a newly-developed setup for performance and lifetime evaluation of DEAs, we investigate how the choice of electrode material and application process influence lifetime. Our investigation is focused on DEAs made from a slide ring material (SRM) as the dielectric. SRM is an interesting candidate for DEAs as it offers a much higher permittivity (epsilon(r) > 7) than commonly used silicone rubbers. However, the log-term durability of SRM DEAs, and how it is influenced by external factors such as the type of electrode material, has not yet been thoroughly studied. We tested SRM DEAs made with various carbon-based electrode materials, different application methods including blade casting, inkjet- and pad-printing, and ink formulations with different solvents. Average lifetime of the DEAs at 50 Hz and 40 V/mu m varied from under 1 h (160,000 cycles) to over 100 h (16,000,000 cycles) between the different electrode types. Our experiments show that not only the type of material but also the thickness and topology of the electrode layer can greatly influence lifetime. We observed that some solvents such as isopropyl alcohol cause swelling and wrinkling of the SRM membrane, but that this has no negative impact on lifetime. We propose that high electrode resistance can improve lifetime by limiting current and reducing the damage from heating, arcing, or partial discharge. This effect can also be achieved by addition of an external resistor. Our results suggest that charge and discharge current of DEAs should always be limited to the very minimum needed for the intended application in order to reduce degradation.