Influence of humidity, temperature and prestretch on the dielectric breakdown strength of silicone elastomer membranes for DEAs

Abstract

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.

Stable and High‐Strain Dielectric Elastomer Actuators Based on a Carbon Nanotube‐Polymer Bilayer Electrode

“…Moreover, this thin WPU layer is as compliant as non‐prestretched VHB films, as shown in the stress‐strain curve (Figure S3A, Supporting Information). The table in Figure S3B in the Supporting Information compares the modulus of 200% biaxially pre‐stretched VHB and WPU films, [ 48 ] and it shows that the WPU film has the same modulus magnitude (10 5 Pa) as the 200% uniaxially pre‐stretched VHB film, indicating that the overcoated WPU layer does not add substantial stiffness to the actuators. Thus, the bilayer SWNT+WPU electrode is chosen to improve the actuation stability and durability of acrylic‐based DEAs.…”

Highly Stretchable Silicone Elastomer Applied in Soft Actuators

“…Another approach for reducing DE film thickness is through prestretching. This process circumvents the need to prepare reliable ultrathin films (<20 μm), and it is a widely known technique to improve dielectric breakdown strength [31,32] however, some chal-lenges remain. First, the reduction in thickness is limited by the stretchability of the elastomers used, as conventional silicone elastomers usually have maximum strains below 900% in uniaxial deformations.…”

Squeezing More Juice out of Dielectric Elastomer Generators

“…The cyclic mechanical deformation needs to be chosen far from the rupture limit of the elastomer for two reasons: 1) to avoid fatigue of the dielectric membrane (Bruch et al, 2020), and 2) to avoid degradation of the compliant electrodes (Rosset et al, 2017;de Saint-Aubin et al, 2018). In addition, the electric field in the structure must be limited to a value well below the dielectric breakdown limit of the material to ensure long-term operation, as parameters such as humidity can influence the breakdown field (Fasolt et al, 2019;Albuquerque and Shea, 2020). As described in more detail in "The energy harvesting cycle" section, combining these two effects leads to a harvestable energy density of the order of 0.1 J g −1 for a DEG using silicone elastomer as dielectric, i.e.…”