Multilayer structural design (including sandwich structure) has received wide attention due to its complementary advantages of different layers in the field of high energy density dielectric materials. Although multilayer polymer composites with improved breakdown strength and energy density have been prepared in some studies, the key mechanism is not clear. In this work, different kinds of multilayer films consisting of various pure polymer [polyimide, poly(vinylidene fluoride) (PVDF), and polypropylene (PP)] layers were prepared to investigate the underlying mechanism of improved performances by multilayer structural design. Experimental results indicated that the relative position of the multilayer film and electrode had an effect on the result of breakdown strength. Meanwhile, when the layer with high relative permittivity (high-k layer) came in contact with the negative electrode, the thinner the high-k layer was, the more remarkable the enhancement of the multilayer materials breakdown strength was. Finally, a double-layer film of PP and PVDF with a Weibull breakdown strength of 649.31 MV/m, which was 60.83 MV/m higher than that of the commercial PP film, was prepared. The simulation result showed that the coating high-k layer could effectively restrain the local electric field distortion around the defect. This study reveals an effective way to improve the breakdown strength of films, which is of great significance for the improvement of capacitor performance and enhancement of energy storage.

Highly aligned polyimide (PI) and PI/multi-walled carbon nanotubes (PI/MWCNTs) nanofibrous composites by incorporating poly(ethylene oxide) as the dispersing medium were fabricated using electrospinning technique. The morphology, mechanical, and electrical properties of the electrospun nanofibrous composites were investigated. Scanning electron microscope showed that the functionalized MWCNTs (f-MWCNTs) were well dispersed and oriented along the nanofiber axis. Analysis of electrical properties indicated a remarkable improvement on the alternating current conductivity by introduction of the aligned f-MWCNTs. Besides, with addition of 3 vol. % f-MWCNTs, the obvious enhancement of tensile modulus and strength was achieved. Thus, the electrospun PI/MWCNTs nanofibrous composites have great potential applications in multifunctional engineering materials.

With the increasing application of barium titanate (BaTiO₃) in polyvinylidene fluoride (PVDF), the evaluation of its dielectric properties has attracted the attention of many frontier scholars. In this paper, from the theoretical point of view, the effects of the aspect ratio and the concentrations of BaTiO₃ nanowires on macroscopic dielectric properties were studied by the finite element method. Depending on the calculation results, some conclusions had been obtained: First, it was found that the effect of higher aspect ratios of nanowires on the effective permittivity of the composites was not significant when the aspect ratio of the nanowire filler exceeded 20. Second, when the permittivity of the BaTiO₃ nanowires reaches about 3000, as the permittivity of the filler increases, the rate of change of the effective permittivity of the composite material gradually slows down, which indicates that nanowires with higher permittivity have little influence on the effective permittivity of the composites. Finally, by comparing with permittivity data of BT/PVDF composites in the literature, it was found that the simulation results have good consistency with the experimentally measured values. The above-mentioned results have shown that the composite may exhibit good dielectric properties at a low concentration (<30 vol. %) and low permittivity filler. Moreover, the electrostatic field can roughly represent the electric field of a low-concentration composite under a certain electric field strength.

The effect of the intrinsic properties of silicone rubber and barium titanate (BaTiO3) nanoparticles on the piezoelectric properties of BaTiO3/silicon rubber composites was studied by the finite element analysis. The data of the simulation show that the stress and voltage of the composite were greatly increased when the concentration of the BaTiO3 nanoparticle increased from 5 to 30 vol. %. As Young’s modulus of silicone rubber increased from 5 to 20 MPa, the compressive stress of the composites raised linearly. With the Poisson’s ratio rising from 0.41 to 0.49, the compressive stress increased by 0.18 MPa in the process. When the dielectric constant of the BaTiO3/silicon rubber composite was less than 30, the potential difference of the piezoelectric film gradually raised with the dielectric constant increasing. When the dielectric constant of the composite was higher than 30, the output voltage of the composite gradually decreased. Therefore, the lower Young’s modulus and Poisson’s ratio of the silicone rubber composite is beneficial to improve the piezoelectric properties of the composite. This article will provide a reference for designing the preparation of spherical BaTiO3 composite materials.

Cu(C₁₀H₁₁O₂N₂)₂ (1) and [Zn(C₁₀H₁₂O₂N₂)₂(H₂O)₂](NO₃)₂ (2) were synthesized and characterized by elemental analysis, FT-IR spectra, UV-Vis absorption spectroscopy, and X-ray single-crystal diffraction. Both complexes show distorted octahedral geometry. In 1, Cu(II) is coordinated by four oxygen atoms from four ligands and two nitrogen atoms from two ligands. In 2, Zn(II) is coordinated by two oxygen atoms and two nitrogen atoms from two ligands, and two water molecules. The crystal structures suggest that original ligand o-carboxybenzaldehyde salicyloylhydrazone (C₁₅H₁₂O₄N₂) changed into acetone salicyloylhydrazone (C₁₀H₁₂O₂N₂). The TG-DTG curves of these complexes indicate two different decomposition processes. 1 and 2 display catalytic activities to decomposition of hydrogen peroxide. Interaction between the complexes and DNA studied by UV-Vis titration shows the insert interaction.

Dielectric elastomer actuators (DEA) are lightweight and compliant actuators for soft crawling robots, but converting actuator deformation into stable directional locomotion remains challenging because of structural compliance, passive foot-ground interaction and material hysteresis. In this work, a soft crawling robot driven by a rolled DEA (RDEA) is designed, fabricated and experimentally evaluated. The robot consists of a spring-supported rolled actuator and two passive asymmetric-friction feet, which convert voltage-induced axial deformation into forward crawling motion. An equivalent finite element model of the active rolled actuator was developed in ABAQUS to analyse the voltage-dependent axial deformation under equibiaxial pre-stretching, spring pre-compression and Maxwell-pressure loading. Under a 300% × 300% pre-stretch and a driving voltage of 7 kV, the model predicted an electrostatic deformation ratio of 16.9%, providing the kinematic input for estimating the ideal crawling velocity. A square-wave voltage driving system was then used to evaluate the crawling behaviour of the fabricated prototype under fixed test-surface conditions. The robot reached a maximum measured crawling speed of 4 mm s ⁻¹ at 7 kV and 2 Hz, corresponding to approximately 0.04 body lengths per second. The measured velocity was lower than the ideal estimate, mainly because of foot slip, frictional dissipation, structural compliance, dielectric loss and elastomer viscoelasticity. These results indicate that a RDEA combined with passive asymmetric-friction feet provides a simple actuation scheme for compact soft crawling mechanisms, while improvements in foot design, electrical efficiency and long-term motion stability remain necessary.