Materials for dielectric elastomer actuators

Abstract

Dielectric elastomer actuators consist of an elastomer film sandwiched between compliant electrodes. They work as electrostatic actuators: when a large electric field is applied over the electrodes, the rubber is compressed and the elastomer film elongates in the film plane. The performance of dielectric elastomer actuators (DEA), when a constant potential is applied, is expressed in a universal equation where a combination of the elastomers materials properties enters through a single parameter - a figure of merit. The expansion of the actuator is related to the applied potential for a particular actuator geometry: an actuator that expands under constant width. The derivation takes finite elasticity of the elastomers into account. The figure of merit can be used as guide to optimizing elastomer properties for dielectric elastomer actuators. For very highly pre-strained elastomers, the equations no longer hold. Elastomers with optimal properties are not commercially available. Typical elastomers for electric applications, encapsulation of electronics take an example, show at least one materials property that diminish their performance in DEA. Elastomers are mapped in a diagram expressing the property space for DEA. Dynamical properties of dielectric elastomer actuators depend upon both electric and mechanical properties of the elastomer. The viscoelastic mechanical properties are intimately connected to network structure of the elastomer. The connection between network structure and the various relaxation times for the rubber that determines its viscoelastic properties are described.