The fabrication of dielectric elastomers from silicone rubber and barium titanate: employing equi-biaxial pre-stretch to achieve large deformations

Barium titanate (BaTiO₃, BT), which has a high dielectric constant was used as the filler in silicone rubber (SR) based-DE composites. The BT was added in order to achieve higher voltage-induced strains and decrease the magnitude of the applied electric fields. The morphology of SR/BT composites was observed using a scanning electron microscope. The mechanical property of the SR/BT composites, which was characterized by an equi-biaxial static test, was obtained using a bubble inflation test system. Significantly, an optimum equi-biaxial pre-stretch ratio was determined using this method in order to enhance the actuated strain achieved under an applied electric field. Concurrently, the measurements of dielectric constant and loss tangent were carried out using dielectric spectroscopy. Using the pre-stretch ratio obtained from equi-biaxial testing, the influence of BT content on the electromechanical properties of SR-based DEs was investigated. The results showed that the BT exhibited excellent dispersibility in SR matrices, but agglomerates appeared in the composites with higher filler content. An increase of dielectric constant was obtained by increasing the BT content in SR with low dielectric loss tangents below 0.035 at 0.1 Hz for all films. Also, the composite of SR/BT exhibited hyperelasticity with the minimum secant modulus at the optimised stretch ratio of 1.6. Under this specified pre-stretch ratio, a maximum actuated area strain of approximately 57 % was achieved for the film having a filler loading of 20 wt% BT. This strain corresponded to a relatively low dielectric strength of around 46 V/µm. For all the DE composites tested, a maximum electromechanical energy density (e) of 0.042 MJ/m³ and an electromechanical coupling efficiency (K ²) of 0.59 were obtained for DEs with 30 and 20 wt% BT, respectively.