Combined Effects of Low Frequency, Temperature, and Mechanical Prestretch on the Dielectric Behaviour of Acrylic and Natural Rubber Dielectric Elastomers

Dielectric properties govern the electromechanical response of electroactive polymer (EAP) actuators and the conversion efficiency of EAP generators, with the dielectric constant playing a particularly critical role in determining how effectively such sensors, actuators, and generators perform. This study examines how low frequency, temperature, and mechanical prestretch jointly influence the dielectric constant of two candidate elastomers: acrylic (VHB 4910, manufactured by 3M, USA) and natural rubber (Oppoband 8001 manufactured by OPPO Medical Inc., USA). Measurements were carried out from 1 Hz to 1 MHz over a temperature range of −80 °C to 60 °C and across different configurations of prestretch states (equal biaxial, unequal biaxial and uniaxial prestretches) from λ1 × λ2 = 1 × 1 to 5 × 5. In both elastomers, the dielectric constant decreased with increasing frequency and with temperature shifts away from the optimum, reflecting dielectric relaxation, and declined steadily with increasing prestretch due to restricted dipole reorientation. VHB 4910 showed markedly greater sensitivity, with its permittivity falling by 32.53% at 0 °C compared with only 14.23% for Oppoband 8001, a contrast attributable to the differing polarity of the two polymer backbones. Glass transition temperatures (Tg) were determined from the loss factor peaks obtained experimentally from dynamic mechanical analysis (DMA), giving values of −42 °C for VHB 4910 and −68 °C for Oppoband 8001. These findings establish practical operational temperature limits to guide material selection, particularly for soft robotic applications.