Proposal of a generic constitutive model for deformation-dependent dielectric constant of dielectric elastomers

Abstract

Dielectric elastomers (DEs) are electroactive polymers that could be used as soft actuators, stretchable generators and sensors. Their performance is dependent on both their mechanical and dielectric properties. Particularly, the dielectric constant has been shown to be dependent on the state of mechanical stretch, which has to be comprehensively characterized across different modes of deformation and different classes of DEs. We conduct experiments to characterize the stretch-dependence of dielectric constant for three classes of elastomers: acrylic (VHB), silicone and natural rubber. In our characterization, we selected three distinct modes of mechanical deformation: equal-biaxial, unequal-biaxial and uniaxial. We reviewed the five most common stretch-dependent dielectric constant models and evaluated their fit with our experimental data which were based upon stretch-dependent dielectric constant of elastomers. Comparing all the model fittings, we find that, although the polarization-based lumped parameter model presents the best fit, both localized dipole relaxation and long chain polymer polarization were absent in the model. In view of the statistical long-chain dynamics in elastomers, we therefore propose a generic, semi-empirical inverse power-law relationship to generalize and standardize the characterization of stretch-dependence of dielectric constant along with log–log curve fitting. We hope to establish a consistent and general framework for dielectric characterization of dielectric elastomers.