IET Nanodielectrics最新文献

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.

Polyimides are advanced polymeric materials that are well known for their excellent thermal, mechanical, electrical and chemical resistance properties. As an important kind of high-temperature resistant dielectric material, polyimides have been widely used in various applications such as electronics, microelectronics and electrical fields, due to their high thermal stability, high glass transition temperature (T_g), outstanding dielectric and electrical insulating performance at the high electric field or at high frequencies. Polyimide dielectric materials have a rich variety of reactive monomers, which endows the molecular structures with strong designability and facilitates the regulation of material properties. Moreover, polyimides can be compounded with various functional fillers to achieve the multifunctional dielectric materials with low or high dielectric properties, low dielectric loss and high breakdown strength. Polyimide dielectric materials also have an ease of processability that make them patternable for many types of integrated devices. With the ongoing advancements in a wide range of novel electronic, microelectronic and new energy applications, polyimide dielectric materials have gained increasing interest from both fundamental and applied research. High-performance polyimide dielectric materials are essential for the development of new electronic or electrical devices where further considerations are required, including higher temperature resistance and energy storage, lower dielectric constant and dielectric loss, improved thermal conduction management as well as better reliability or flexibility in harsh environments. In order to meet the more stringent application requirements mentioned above, there is an urgent need to develop polyimide dielectric materials with higher comprehensive performance, which requires joint development through new theoretical designs, new structures, methods, processes and other means. A wide variety of research is being conducted to prepare kinds of functional polyimide dielectric materials to address applicable challenges and explore possible opportunities in different fields. This current Special Issue is focused on ‘High performance polyimide dielectric materials’ and their applications in different topics, emphasising the latest innovations in polyimide or polyimide-based dielectric materials and better understanding of deep relationship between their chemical or composition structures and overall performances.

In this Special Issue, four high-quality papers have undergone peer-reviewed and eventually been accepted for publication. These published papers include five original research papers and one review article in the application field of high-performance polyimide dielectric materials. All the papers can be clustered into three main categories related to dielectric materials, namely preparation, molecular design and measurement or simulation. (

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.

The authors report a novel electret-based miniature electrostatic motor with an electret film as the stator and a metal electrode as the rotor. A particular commutator is used to transform the polarity of the metal electrode. When the size of the electret-based electrostatic motor (EEM) is 42 × 44 × 15 mm³, the maximum power consumption is only 5.4 mW. The rotation speed of the EEM increases with the increase of the supply voltage, and the maximum rotation speed can reach up to 2864 rpm. Powered by two nickel-hydride batteries with a rated capacity of 1700 mAh, the EEM can drive a fan with a diameter of 40 mm to rotate continuously for 18 h. The EEM has the characteristics of low power consumption and convenient fabrication. Experimental results show that the EEM demonstrates high reliability and has potential applications in micro-electromechanical systems.

We have witnessed the flourish of bioelectronics, brain–computer interface, and brain science programme in recent decades. In this review, the up-to-date advances of dielectric, piezoelectric, and ferroelectric nanomaterials in the biomedical applications are summarised. Biomolecular detection methods have been developed, including dielectric-gated field-effect transistor, dielectrophoresis, non-linear dielectric response, and optical tweezer. Endogenous bioelectricity is a crucial in cell proliferation, migration, differentiation, intracellular communication, neuronal activity, tissue growth. Piezoelectric and ferroelectric materials can be utilised as energy transducer to monitor physiological signal, such as blood pressure or respiration, and directly stimulate cell differentiation, neuronal regeneration, tissue repairment etc. They can also catalyse the electrochemical reaction of organisms through piezoelectricity. The intrinsic relevance between neuronal and ferroelectric polarisation signals inspires the application of the ferroelectrics in the modern intelligent bioelectronics like the artificial retina.

Recently, demands for high-performance polymer film capacitors at elevated temperatures have become more urgent. High dielectric constant is essential for dielectric materials to achieve substantial energy density at relatively low electric fields, which is of great significance to practical applications, while improving the permittivity of high-temperature polymer dielectrics without a remarkable deterioration in other electrical properties still remains a challenge. Here, a polymer nanocomposite containing z-aligned high-k nanowires sandwiched by e-beam evaporation deposited Al₂O₃ films was developed based on the optimal structure proposed by the phase-field simulation. It is found that z-aligned nanowires are more effective in promoting the dielectric constant than random-aligned ones, and a large increase in dielectric constant is observed at relatively low content of nanofillers. Outer insulating layers effectively suppress the electric conduction and improve the breakdown strength. Consequently, the nanocomposite with only 1 volume fraction of z-aligned nanowires exhibits a breakdown strength, electrical resistance, and charge–discharge efficiency as high as neat PEI, but more than twice the discharged energy density than it at 150 °C. This study realises the optimal structure predicted by simulation in experiment, obtaining high-permittivity, high-temperature nanocomposites at no expense of other electrical properties, and making it possible to achieve high discharged energy density at relatively low electric fields.

The flashover threshold (V_flsh) of polymer insulations such as epoxy (EP) in HVDC systems can be augmented by modifying their surface with an appropriate treatment technology. For such purpose, several surface treatment methods such as ion beam, sandpaper and a combination of the two is introduced. Firstly, insulation samples with pure epoxy (EP_pure), different ion beam treatment periods (EP_ion;10, 15, 20 min) and different roughness (EP_sand; R1 = 4.23 μm, R2 = 6.34 μm, R3 = 9.21 μm) are prepared on the laboratory scale. Afterward, based on several characterisations, such as surface conductivity, mean surface roughness and potential distribution of these insulations, multi-modified insulation (EP_multi = EP_ion-20 + EP_sand-R3) is prepared. In the end, the V_flsh of each insulation group is measured and compared to examine the effectiveness of the proposed modifications. It is obtained that the V_flsh of the modified insulations augmented dramatically irrespective of the treatment method. The V_flsh of the insulation group EP_multi augmented by 52.66 % which is the highest improvement among all insulation groups. In short, the proposed surface modifications are effective and could be used as references to enhance the insulation strength of polymer dielectrics in HVDC systems.

The high permittivity of polymer dielectrics facilitates their use in the electronics industry. Compared to inorganic ceramics and composites, intrinsic high permittivity polymer dielectrics have the advantages of easy solution processing and better homogeneity. The permittivity of common polymers is generally low, hence it would be worthwhile to explore avenues for augmenting the permittivity of polymer dielectrics via judicious and efficient structural design. The effective strategies used to increase the permittivity of intrinsic polymers encompass elevating local polarisabilities by fortifying electron delocalisation capabilities, exploiting ion pairs to generate atomic clusters with larger dipole moments, amplifying dipole density, augmenting dipole mobility, and so forth. Due to the rigidity and flexibility of the polymer backbone's decisive influence on the dielectric's all-around performance, its selection also requires a total consideration of the requirements of practical applications. This work provides an overview and a brief evaluation of the dominant design strategies and mentions possible future design paradigms for polymer dielectrics.

The concept of self-healing dielectric polymers has been heatedly discussed, with the expectation of high damage resistance and longer service time. However, there is still a lack of analysis on the competitive relationship between electrical degradation and self-healing. The authors discussed this relationship in two stages: the design of self-healing strategies and the operation of self-healing polymers. Since the requirements for excellent insulating or mechanical properties are not consistent with the demands for high self-healing capability, trade-offs are necessary during the design of self-healing polymeric systems. In the operation stage of dielectric polymers, some key factors that affect the service lifetime of non-autonomous self-healing dielectric polymers are analysed, including the efficiency and repeatability of self-healing, and the frequency of healing maintenance. For autonomous self-healing dielectrics, the simultaneous processes of ageing and healing are investigated using a self-healing epoxy resin based on microcapsules and in situ-generated radicals. A quicker recovery of insulating properties, in terms of partial discharge magnitude, was observed under appropriate healing voltages. However, the self-healing ability might vanish when the voltage was too high, verifying the competitive relationship between electrical degradation and self-healing.