Due to some useful mechanical, dynamic, and dielectric properties along with the ease of processing and forming, liquid rubbers are ideal materials for fabricating dielectric elastomer actuators in various configurations and for many potential applications ranging from automation to automobile and medical industry. In this study, we present a cross-linkable liquid rubber composition where amine-catalyzed esterification reactions lead to the formation of a network structure based on anhydride functional isoprene rubber, carboxyl-terminated nitrile-butadiene rubber, and epoxy end-capped prepolymers. The success of this intricate network formation procedure was verified by HR-MAS NMR spectroscopy. The new isoprene-based elastomeric material exhibits actuation-relevant attributes including a low elastic modulus of 0.45 MPa, soft response to an applied load up to a large deformation of 300%, and a dielectric constant value (2.6) higher than the conventional Elastosil silicone (2.2). A dot actuator comprising of an isoprene dielectric elastomer film in unstretched state and carbon paste electrodes was fabricated that demonstrated an electrode deformation of 0.63%, which is nearly twice as high as for the commercial Elastosil 2030 film (∼0.30%) at 5 kV. Compared to the Elastosil silicone film, the enhanced performance is attributed to the low modulus and high dielectric constant value of the new isoprene elastomer.

In this study, we investigated the influence of an epoxy end-capped polypropylene oxide crosslinker (epoxy-PPO) on the formation of the crosslinked network structure, the stress–strain response, and the electro-mechanical actuation performance of a maleic anhydride functionalized liquid isoprene rubber (LIR). The crosslinker amount varied from 10 (C-LIR-10) to 50 (C-LIR-50) weight parts per hundred parts (phr) of LIR. The swelling test of the cured rubbers revealed that C-LIR-20 formed the densest crosslinked network with the lowest chloroform uptake value within this series. The crosslinked rubber became stiffer in tensile response upon increasing the epoxy-PPO amount from C-LIR-10 to C-LIR-20 and then softened at higher amounts. The SEM measurements were used to relate this composition-induced softening of the rubbers to the phase morphology evolution from nanoscale homogeneity in C-LIR-10 to microscale segregations of excess crosslinkers in C-LIR-50. The use of epoxy-PPO improved the dielectric constant value of LIR; however, the leakage current through the films also increased from 25 µA DC to 320 µA DC for LIR-30 and LIR-50, respectively, during DEA operation. The electro-mechanical actuation tests with circular actuators showed that the C-LIR-10 elastomer film demonstrated a radial strain of 1.7% on activation at an electric field strength of 17.5 V/µm. At higher crosslinker amounts, the close proximity of excess epoxy-PPO molecules caused leakage current across elastomer films thus diminishing the actuation strain of otherwise relatively softer elastomers with higher dielectric constant values.