Humidity, temperature and membrane prestretch influence the dielectric breakdown strength of elastomer membranes. These three factors thus also influence the maximum force and strain that dielectric elastomer actuators (DEAs) can generate, as the Maxwell pressure is proportional to the applied voltage squared, and limited by the breakdown field. We compared several commercial silicones, 10 to 25 µm thick under different equibiaxial prestretch conditions, for temperatures between 20 °C and 80 °C and relative humidity from 10% to 90%, measuring both breakdown fields and mechanical properties in order to compute two figures of merit for DEAs. The silicone films all have breakdown strengths of order 100 V µm−1. Higher humidity (90% RH) leads to decreased dielectric breakdown strengths compared to lower humidity (10% RH): up to 43% reduction for prestretches of 1.3 and 1.5, but only 2% to 10% reduction for prestretch of 1.1. Higher prestretch leads to up to 50% higher breakdown field, but also leads to higher effective Young’s modulus due to strain stiffening. Higher temperatures (80 °C) lead to up to 30% lower breakdown voltages compared to lower temperatures (20 °C). Higher prestretch generally enhances the maximum Maxwell stress because of higher dielectric breakdown strength, but reduces the strain figure of merit owing to increased Young’s moduli at high prestretch. For silicone elastomers, Sylgard 184 shows the highest stress figures of merit and LSR 4305 the highest strain figures of merit. Data for VHB is also presented for comparison. This work allows identifying elastomers better suited to harsh environments, and to selecting operating voltages that enable safe operation for a wide range of environmental conditions.

We present the effect of electric field, temperature, humidity, type of elastomer material, and encapsulation on the lifetime of silicone-based dielectric elastomer actuators (DEAs) under DC electric fields. DEAs are promising soft actuators, but little has been reported on their reliability under static electric fields. We report that humidity and electric field are the dominant accelerating factors for device failure, and that a thin encapsulation layer can increase lifetime by more than an order of magnitude with negligible reduction in actuation strain. Our samples are expanding circle, single layer, prestretched films with 5 mm diameter compliant electrodes, operated at electric fields from 80 V µm−1 to 110 V µm−1, with actuation strains from 2% to 6%. We compare four different silicone elastomers, finding highest lifetime with Momentive Electro 242-1, five times higher than Elastosil 2030. Typical mean time to failure (MTTF) for Elastosil 2030 based DEAs at 100 V μm−1, 85 °C and 85% RH are 1.6 h, but this value increases to over 200 h at 20% RH. At 85 °C and 85% RH, the MTTF decreases by a factor of 62 when increasing the electric field from 80 V μm−1 (2.1% actuation strain) to 100 V μm−1 (4.6% actuation strain). Adding a thin, soft silicone encapsulation layer is an effective yet simple strategy to increase DEA lifetime, increasing the MTTF by factors from 2.2 to 75 under humid conditions. Extrapolating from our data, we predict that DC lifetimes above 1000 h can be achieved at fields below 70 V μm−1 (i.e. ≈1.5% strain) for Elastosil 2030/20 DEAs, and below 85 V μm−1 (i.e. ≈2.5% strain) for encapsulated DEAs at 85 °C—85% RH.

We present an automated test setup for the systematic performance and lifetime evaluation of dielectric elastomer actuators (DEAs). This setup, called the MAPLE setup, performs accelerated aging tests and allows quantifying how material choice, fabrication methods, voltage waveform, and environmental conditions influence DEA lifetime, an important step for commercial use of DEAs. The setup continuously monitors strain and electrode resistance of multiple DEAs under a wide range of environmental conditions (up to 85 °C and 85% relative humidity), with automatic breakdown detection to record device lifetime. To illustrate a use case, we investigate the lifetime of DEAs made of two different elastomer materials, comparing fixed polarity (FP) vs. periodically reversing the polarity of the actuation voltage. For DEAs made from a slide-ring material, lifetime improvements around 10× were observed at alternating polarity compared to FP. For DEAs made from silicone rubber, no improvement in lifetime was observed. This indicates that different degradation mechanisms are causing failure in the two materials.

No abstract

No abstract