Soft composite actuators of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene)-based nanofibers and polydimethylsiloxane: Fabrication, electromechanical characterization, and dynamic modeling

Nanofibrous unimorph cantilever beam soft actuators offer remarkable advantages, such as rapid viscoelastic relaxation, low power consumption, and high weight-specific properties. However, the presence of high porosity in the nanofibrous active layer poses a challenge due to its low breakdown voltage, limiting the practical applications of this class of soft actuators. This study proposes an innovative solution to enhance the relative permittivity of the nanofibrous layer by redesigning it as a composite layer. By integrating electrospun aligned nanofibers of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) into a polydimethylsiloxane elastomeric matrix, the composite active layer achieves a notable increase in relative permittivity (10.5 at 100 Hz), surpassing the individual materials' values (2.5 and 2.7 at 100 Hz for the nanofibers and polydimethylsiloxane, respectively). To realize novel soft actuators, the composite active layer is placed between carbon black electrodes, with Kapton (R) serving as the passive layer. Remarkably, aligning the nanofibers in the transversal direction of the actuator enhances its actuation capabilities significantly. When subjected to a 25 MVm-1 electric field, the tip deflection and blocking force exhibit a similar to 400% improvement compared to polydimethylsiloxane-based actuators. To support these findings, a physics-based dynamic model is derived and validated through experimental tests in both static and transient time simulations.