A dielectric elastomer is capable of giant electromechanical actuation but fails at breakdown due to instability under certain conditions with a small deformation. By applying a mechanical pre-stretch, one obtains a stabilized large actuation. In this paper, we measured the dielectric constant and critical voltage of a polyacrylic dielectric elastomer subjected to both equal and unequal biaxial stretch, and modelled its actuation by employing the Gent strain energy function with a microscopic view to characterize the nonlinear stiffening behaviour and the electrostrictive effect in the deformation. The mechanical pre-stretch contributes in several ways to the stabilization of dielectric elastomer, by eliminating the pull-in instability, by generating electrostriction, by improving the breakdown strength, as well as by reducing the membrane thickness which consequently lowers the voltages required for activation.
The dielectric constant of elastomeric dielectric material is an essential physical parameter, whose value may affect the electromechanical deformation of a dielectric elastomer actuator. Since the dielectric constant is influenced by several external factors as reported before, and no certain value has been confirmed to our knowledge, in the present paper, on the basis of systematical comparison of recent past literature, we conducted extensive works on the measurement of dielectric properties of VHB films, involving five influencing factors: prestretch (both equal and unequal biaxial), electrical frequency, electrode material, stress relaxation time and temperature. Experimental results directly show that the dielectric response changes according to these factors, based on which we investigate the significance of each factor, especially the interaction of two external conditions on the dielectric constant of deformable dielectric, by presenting a physical picture of the mechanism of polarization.
Elastic dielectrics are able to produce large deformations as dipoles align in the direction of an electric field. We proposed a model to study the polarization mode, named conditional polarization, and to characterize the behavior when the dipolar alignment is constrained by deformation. Combined with experimental measurements, we applied the model to investigate the electromechanical deformation of a dielectric membrane. The conditional polarization would modify the final state as well as the path to instability during actuation due to the mechanism of induced electrostriction, indicating a new route to optimize the performance of elastic dielectrics.
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