IET Nanodielectrics最新文献

With an increasing demand for environmentally friendly refrigeration, the solid-state refrigeration based on the electrocaloric effect (ECE) has been drawn extensive attention. It is a challenge to maintain a large adiabatic temperature change (∆T) over a broad temperature span. Herein, the authors designed and synthesised (0.74-x) Na_0.5Bi_0.5TiO₃-0.06BaTiO₃-0.2SrTiO₃-xBi(Mg_0.5Zr_0.5)O₃ (abbreviated as NBT-xBMZ) (x = 0, 0.02, 0.04, 0.06 and 0.08) lead-free relaxor ferroelectrics. Their microstructures, dielectric properties, ferroelectric properties, ECEs and the structure-property relationships were investigated. Via doping with BMZ, an enhanced relaxor feature and a wider temperature range where multi-phases coexist were achieved. The relaxor ferroelectric characteristics were illustrated using the Vogel-Fulcher relation. The indirectly calculated ECE results showed that the optimal ΔT of 1.11 K was obtained for the x = 0.02 sample at 90°C and 70 kV/cm over a wide T_span of 120°C, providing a potential ECE material. The direct ECE results procured using thermocouple indicated that the maximal ∆T of 2.14 K and ∆T/∆E of 0.31 K m/MV were achieved in the same sample at 70°C and 7 MV/m and the variation trend of ECE results was consistent with the indirect results. Moreover, the multi-phases coexistent strategy can be extended to other materials system to generate a large ΔT over a wide temperature range.

The demand for innovative thermal management materials with superior thermal conductivity and electrical insulating properties has significantly increased with the development of portable and flexible electronic gadgets. Fluorinated graphene (FG) has recently attracted the attention of the scientific community because of its exceptional thermal conductivity and electrical insulating qualities. This work aims to provide a detailed analysis of the structure-property relationships inherent in FG, including both chemical and physical properties, and to explain the FG manufacturing process. Special attention should be paid to a thorough analysis of the thermodynamic conduction mechanism exhibited by FG, including the effects of corrugation size, fluorine coverage, and fluorine atom distribution on its thermal conductivity. The essay also examines in-depth the most current and cutting-edge developments addressing the utilisation of FG as a functional filler in composite-modified polyimide (PI) materials. Furthermore, it has been noted as a crucial component in answering the needs for possible applications by maximising thermal conductivity and mechanical qualities in FG/PI composites through particular FG structural engineering and increased FG-PI interaction. As a result, these elements serve as the main focus of ongoing research projects, highlighting important directions for development and investigation.

A series of siloxane-containing polyimide films (PIS) were prepared by copolymerising with rigid aromatic dianhydride, siloxane diamines and six different aromatic diamines. The effects of siloxane structures, fluorine and imide content, rigid or flexible segment on the heat resistance, moisture absorption, dielectric performance, mechanical and bonding properties were systematically studied. The results show that PIS films maintain good heat resistance with T_g between 292 and 420°C and 5% weight loss temperature higher than 500°C. The moisture absorption and dielectric constant can be significantly reduced due to the presence of siloxanes and fluorinated groups, with the absorption rate as low as 1.2% and dielectric constant of 2.85 at 1 MHz. When measured at 10 GHz, the dielectric constant ranges from 3.10 to 3.50, and dielectric loss varies from 0.0059 to 0.0098. The PIS-6 film has the best comprehensive performance due to the low imide content, introduction of trifluoromethyl and ether bonds. The peeling strength of bonding PIS-6 film with a copper foil can reach 9.2 N/cm. It is proven that siloxane-containing PIS films with high heat resistance, low dielectric and outstanding adhesion are achieved, which can be applied for flexible integrated circuit boards, high-frequency electronics and microelectronics fields.

With a large number of film capacitors being deployed in critical locations in electrical and electronic systems, artificial intelligence (AI) technology is also expected to address the problems encountered in this process. According to our findings, AI applications can cover the entire lifecycle of film capacitors. However, the AI safety hazards in these applications have not received the attention they deserve. To meet this, the authors argue, with specific examples, risks that flawed, erratic, and unethical AI can introduce in the design, operation, and evaluation of film capacitors. Human-AI common impact and more multi-dimensional evaluation for AI are proposed to better cope with unknown, ambiguity, and known risks brought from AI in film capacitors now and in the future.

This article deals with the improvement of the dielectric properties of TUK cellulose paper by impregnation. The experiment was carried out using a nanofluid based on vegetable oil esters and iron nanoparticles (FeO₃). The insulating liquids used are palm kernel oil methyl ester (PKOME) and castor oil methyl ester (COME). The evaluation of the improvement is based on the analysis of the flashover voltage of the creeping discharges produced on the immersed paper. The tests were carried out under a positive lightning impulse voltage and for two electrode configurations. The concentrations of nanoparticles used in the experiment are 0.10 wt.%, 0.15 wt.% and 0.20 wt.%. The experimental results show that the 0.10 wt.% concentration gives the best improvement for the two electrode configurations used. The improvements are 53% for the inclined tip and 56.90% for the vertical tip in the case of COME + FeO₃. For PKOME + FeO₃, the results are 59.90% and 64.60%, respectively, for the two configurations.

Continuous three-dimensional BaTiO₃ (3DBT) ceramic network was prepared by the sol-gel method using cleanroom wipers as the template. Subsequently, flexible 3DBT/polyvinyl alcohol-boron nitride nanosheets (PVA-BNNS) composite dielectric films were facilely fabricated by inversely introducing different BNNS concentrations of PVA-BNNS solution into the 3DBT network. The results demonstrated that PVA solution effectively embedded into the 3DBT framework through an inverse infiltration process, thereby endowing the material with excellent flexibility. The content of 3DBT in the saturated 3DBT/PVA-BNNS composite was ∼27 wt% (6.9 vol%). In addition, the 3DBT/PVA-1.0%BNNS system exhibited an excellent dielectric constant of 17.4 (at 1 kHz), a high breakdown strength of 114.5 kV·mm⁻¹ and an energy density of 2.51 J·cm⁻³ (at 110 kV·mm⁻¹), being 1.67, 1.58 and 7.17 times higher than those of traditional fabricated 27 wt% nano-BT/PVA (at 70 kV·mm⁻¹) composite, respectively. What's more, the obtained 3DBT/PVA-BNNS dielectric film exhibited superior thermal and mechanical stability, indicating potential applications in harsh environments.

Bacterial biofilm is an important factor in bacterial drug resistance. Recently, it has been proved that electret films can inhibit the bacterial biofilm, while its mechanism of action on biofilms is under further investigation. In this work, taking Staphylococcus aureus as an example, the inhibition of positive electret on bacterial biofilm was verified and its mechanism was explained. Two factors have been found to explain the inhibition mechanism of electret on bacterial biofilms. One is probably due to its inhibition of the expression of key genes related to bacterial biofilms induced by the electric field of positive electret, and the other is to prevent the aggregation of bacteria rather than the direct bactericidal effect. The conclusions are expected to be extended to other types of bacteria and expand the application of electrostatic materials in the field of biomedicine.

Polymer dielectrics with excellent thermal resistance and superior energy storage behaviour are extensively demanded with the increasing development of film capacitors applied in hostile environments. In this study, novel diamine with sulfonyl-containing side chain was designed and synthesised. The corresponding polyimide (PI) dielectrics derived from the sulfonyl-containing diamine were prepared, so were the polyimides possessing the same backbone but without side chains. Consequently, superior thermal resistance of glass transition temperature ranged from 162–208°C was obtained. Moreover, the polyimides presented permittivity of 3.34–5.89 at 1 kHz, Weibull breakdown strength of 377–538 MV/m and discharged energy density of 3.82–5.85 J/cm³. In particular, sulfonyl-containing polyimide of SPI-2 with flexible backbone and sulfonyl side chain indicates the highest discharged energy density and charge-discharge efficiency simultaneously. The introduction of the strong polar sulfonyl group in the side chain enhances dielectric and energy storage properties effectively. In addition, it is found that the dipolar moment density (μ/V_vdw) calculated from molecular simulation is closely correlated to permittivity measured from experiments. The combined method of molecular simulation and experiments would offer an effective approach to assist in molecular design of high-performance polymer dielectrics.