Improved Electromechanical Coupling in Silicone-Based Elastomer Thin Membranes Filled by Silica-Coated Multiwalled Carbon Nanotubes

Abstract

Dielectric elastomers (DEs) are flexible, voltage-responsive materials that can undergo significant deformations upon being subjected to high actuation electric fields. Their efficient electromechanical conversion, along with their ability to operate across a wide frequency range, makes them highly promising for mechatronic applications. Herein, we propose DE nanocomposites based on silica-coated multiwalled carbon nanotubes (CNT@SiO 2 ) dispersed in liquid silicone rubber (LSR) elastomer thin membranes sandwiched between highly conductive and stretchable compliant electrodes made from carbon-black airbrushed ink. Dielectric spectroscopy showed an enhancement of dielectric constant from 2.6 of pure polymer up to 5.9 at 1 kHz, keeping a low dielectric loss of 0.0055 also under the effect of DC voltage bias of 100 V. High-voltage C−V hysteresis loops were employed to detect dielectric breakdowns occurring well beyond the actuation fields. Such DE nanocomposites showed outstanding elastic properties in a uniaxial tensile test at different elongation rates with a variation of Young's modulus from 0.024 to 0.084 MPa for a filling fraction of 2.0 wt. Moreover, precycling treatments showed Mullins effects softening with the decreases of elastic properties from 67 to 50% from low to high elongation rates for the LSR pure polymer and from 20 to 7% for CNT@SiO 2 -based DE nanocomposites. Further biaxial tensile tests were performed on the final device comprising membranes sandwiched by highly stretchable compliant electrodes showing comparable elastic properties (0.029−0.033 MPa), indicating the negligence on the mechanical properties by the presence of thin layers of conductive ink. Furthermore, the CNT@SiO 2 -based DE nanocomposites demonstrated an actuation strain exceeding 125% in comparison with the pure polymer for the same applied electric field, suggesting a scalable membrane fabrication process suitable for the efficient development of electroactive soft materials.