Soft Gel Filler Embedded Elastomer with Surfactant Improved Interface for Dielectric Elastomer Actuators.

Stretchable materials are the foundation of dielectric actuators (DEAs) for artificial muscle. However, the inadequate dielectric constant of stretchable materials has always greatly limited the performance of artificial muscle. Recently, soft fillers have been proposed to improve the dielectric property and preserve the stretchability for softness, aiming to avoid the stiffening effect of traditional rigid fillers. As composites, an amount of interfacial region is generated, which remarkably affects composites' performance from dielectrics to mechanics. Herein, we demonstrate that the size effect, interfacial binding, and compatibility have a great impact on soft filler doped composites. Particularly, according to the liquid characteristics of soft fillers, we explore an interfacial modification method using surfactants. Composite breakdown strength is thus enhanced 2.2-fold from that in the control group due to the reduction of mismatch between fillers and matrix. Moreover, surfactants alleviate the well-known stiffening effect in small fillers. The area strain of the composites reaches 10.3 ± 0.4% at a low electric field of 7 MV/m, and a soft micropump is successfully assembled. These findings demonstrate a unique and combined interfacial influence of soft filler doped elastomer, which promotes the advancements of the dielectric elastomer artificial muscle.

Novel Route for Enhancing Piezoelectricity of Ferroelectric Films: Controlling Nontrivial Polarization States in Pb(Zr, Ti)O3 Monodomain Superlattice Structure.

Artificial superlattice films made of Pb(Zr0.4Ti0.6)O3 and Pb(Zr0.6Ti0.4)O3 were investigated for their polarization states and piezoelectric properties theoretically and experimentally in this study. The developed theory predicts nontrivial polarization along neither [001] nor [111] directions in (111)-epitaxial monodomain superlattice films with uniform compressive strain. Such films were achieved via pulsed laser deposition. When the layer thickness is reduced to 3 nm, d33 becomes 128 ± 3.8 pm/V at 100 kV/cm and 71.3 ± 2.83 pm/V at 600 kV/cm, comparable to that of (111)-oriented Pb(Zr0.4Ti0.6)O3 or Pb(Zr0.6Ti0.4)O3 bulks and clearly exceeding that of the typical clamped films. The measurement agrees with the theoretical analysis, which reveals that the enhanced piezoelectricity is due to rotation of the nontrivial polarization. Furthermore, the theoretical study predicts an even larger d33 exceeding 300 pm/V for specific parameters in superlattice films with uniform tensile strain, which is promising for applications of microelectromechanical systems.

Design optimization of PVDF-based piezoelectric energy harvesters.

Energy harvesting is a promising technology that powers the electronic devices via scavenging the ambient energy. Piezoelectric energy harvesters have attracted considerable interest for their high conversion efficiency and easy fabrication in minimized sensors and transducers. To improve the output capability of energy harvesters, properties of piezoelectric materials is an influential factor, but the potential of the material is less likely to be fully exploited without an optimized configuration. In this paper, an optimization strategy for PVDF-based cantilever-type energy harvesters is proposed to achieve the highest output power density with the given frequency and acceleration of the vibration source. It is shown that the maximum power output density only depends on the maximum allowable stress of the beam and the working frequency of the device, and these two factors can be obtained by adjusting the geometry of piezoelectric layers. The strategy is validated by coupled finite-element-circuit simulation and a practical device. The fabricated device within a volume of 13.1 mm3 shows an output power of 112.8 µW which is comparable to that of the best-performing piezoceramic-based energy harvesters within the similar volume reported so far.