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Epoxy resin (EP) has been widely utilized in electrical equipment and electronic devices due to its fascinating electric, thermal, and mechanical properties. However, the complex insulation structures of modern power devices in high-voltage direct current systems pose several challenges for EP-based dielectrics. The most significant among these challenges is the need for EP to stably operate under greater electric fields, requiring superior breakdown strength. This paper summarizes the key factors influencing the breakdown strength of EP and reviews reported methods for enhancing this property. Recognizing the limitations of existing approaches, we propose that the emerging technology of molecule design offers a potentially optimal solution for developing EP with enhanced breakdown strength. Furthermore, we anticipate the future development direction of EP with satisfactory insulation properties. We believe that enhancing the breakdown theory of solid dielectrics, exploring new research and development methodologies, and creating environmentally friendly EP with high performance are primary focus areas. We hope that this paper will offer guidance and support for the future development of EP with superior breakdown strength, proving valuable in advancing EP-based dielectrics.

Surface flashover that occurs on the surface of epoxy resin (EP) is one of the main causes of insulation failure in the power system. The newly emerging polar groups on the surface are highly desirable for enhancing the surface flashover performance of EP. Here, we present a facile ultraviolet (UV) irradiation method to enable the controlled introduction of C–OH and C = O groups on the EP surface. The resultant UV-irradiated EPs (UV-EPs) are highly uniform with little variation in surface roughness while exhibiting tunable polar content with the irradiation time. We also present the first systematic investigation into the effect of UV irradiation time on the surface flashover voltage of UV-EPs, with a maximum increase of 23.07% compared to the pristine EP. Mechanistic studies suggest that the enhancement of the surface flashover voltage is mainly dominated by the density of the deep trap, which is strongly dependent on the UV-induced C–OH and C = O groups on the surface. Besides that, the UV-EPs also display long-term stability due to the stable presence of polar groups, which further demonstrates the feasibility of this method for the development of EP with excellent properties. [ABSTRACT FROM AUTHOR]

Polymer dielectrics with excellent capacitive performance are urgently needed in advanced electrical and electronic systems. However, due to the dramatic increase in the conduction loss, the energy density and efficiency of polymers degrade severely at elevated temperatures, limiting their application in harsh environments up to 150 °C. Herein, an all-organic polyurea (PU)/polyetherimide (PEI) blend film is designed to prepare high-temperature polymer dielectric. It is found that carrier traps can be introduced by blending, and the hydrogen bond between PU and PEI increases the trap depth, leading to suppressed leakage current and enhanced breakdown strength, thus improving the energy storage performance. PU/30%PEI exhibits a high discharged energy density of ∼3.74 J/cm3 with an efficiency higher than 90% at 150 °C, which is 78% and 70% higher than pristine PU and PEI, respectively. This work provides a facile strategy to improve the energy storage performance of polymer dielectrics by introducing deep traps through blending. [ABSTRACT FROM AUTHOR]

SUMMARY: The interplay between microRNAs (miRNAs) and phytohormones allows plants to integrate multiple internal and external signals to optimize their survival of different environmental conditions. Here, we report that miR394 and its target gene LEAF CURLING RESPONSIVENESS (LCR), which are transcriptionally responsive to BR, participate in BR signaling to regulate hypocotyl elongation in Arabidopsis thaliana. Phenotypic analysis of various transgenic and mutant lines revealed that miR394 negatively regulates BR signaling during hypocotyl elongation, whereas LCR positively regulates this process. Genetically, miR394 functions upstream of BRASSINOSTEROID INSENSITIVE2 (BIN2), BRASSINAZOLEs RESISTANT1 (BZR1), and BRI1‐EMS‐SUPPRESSOR1 (BES1), but interacts with BRASSINOSTEROID INSENSITIVE1 (BRI1) and BRI1 SUPRESSOR PROTEIN (BSU1). RNA‐sequencing analysis suggested that miR394 inhibits BR signaling through BIN2, as miR394 regulates a significant number of genes in common with BIN2. Additionally, miR394 increases the accumulation of BIN2 but decreases the accumulation of BZR1 and BES1, which are phosphorylated by BIN2. MiR394 also represses the transcription of PACLOBUTRAZOL RESISTANCE1/5/6 and EXPANSIN8, key genes that regulate hypocotyl elongation and are targets of BZR1/BES1. These findings reveal a new role for a miRNA in BR signaling in Arabidopsis. Significance Statement: miR394 and its target gene LEAF CURLING RESPONSIVENESS are involved in BR signaling by affecting BRASSINOSTEROID INSENSITIVE2 accumulation. [ABSTRACT FROM AUTHOR]

Polythioureas (PTUs) show great potentials for applications in the new generation of film capacitors due to their excellent dielectric properties. Herein, the cis‐trans copolymer chain of PTU is successfully tailored by employing cis and trans cyclohexyl spacers. The relationship between the copolymer chain conformation, microstructure, and dielectric properties is carefully explored by a series of analysis. Compared with cis conformation, the trans with less steric hindrance can promote the formation of H‐bonds. The enhanced H‐bonding interactions not only reduce the molecular inter‐chain spacing, but also drive the self‐assembly of molecular chains to form cylindrical and droplet nano‐morphologies. The phase separation between cis and trans PTUs is confirmed by combining the experimental results of TEM and DSC, and the CT64‐PTU with the most two‐phase interface thus obtains the highest permittivity of 5.5 (@10 Hz). The reduced molecular inter‐chain spacing is accompanied by a decreased hopping distance of charges, which improves breakdown strength by 17% from 498 MV/m to 580 MV/m. Therefore, the cis‐trans copolymer chain conformation in PTU provides a simultaneous high permittivity and breakdown strength. This research offers a strategy to further design high‐performance dielectrics via regulation of copolymer chain conformation. [ABSTRACT FROM AUTHOR]

To date, numerical simulation techniques for surface flashover are still under development. In this work, a DC surface flashover numerical simulation model is constructed based on a gas–solid coupling surface flashover theoretical model with a multilayered structure at the gas–solid interface. Considering the effects of solid, gas, and gas–solid interaction on surface flashover, bipolar charge transport in the solid surface layer, collision ionization in the gas phase layer, secondary electron emission, and gas adsorption in the gas surface layer are combined to calculate the surface flashover voltage. By initializing model parameters, surface charge transport dependent dc surface flashover voltages of epoxy composites in compressed nitrogen are calculated. The results indicate that the surface flashover voltage increases with surface deep trap level, deep trap density, shallow trap density, and carrier mobility; however, surface flashover voltage decreases with surface shallow trap level and surface charge density. To further investigate the effects of surface trap on surface flashover, a "U-shaped" curve is constructed to describe the relationship between surface flashover voltage and surface trap level by the simulation method which shows good agreement with experimental results. The simulation indicates surface flashover voltage of epoxy composites is influenced by surface deep and shallow traps in the solid surface layer—shallow traps mainly influence surface charge dissipation, while deep traps mainly influence electron emission on the solid surface. The value of Ptr/Pde is crucial for the dominating surface trap in surface flashover. [ABSTRACT FROM AUTHOR]

Surface flashover is likely to be triggered when a high electric field is applied due to its voltage being much lower than the breakdown voltage of either gas or solid, which restricts the development of advanced power electrical and electronic devices. To improve dc surface flashover performances in a vacuum and further explore the effects of deep traps on surface flashover, conductive multiwall carbon nanotubes (MWCNTs) and nonconductive nano-titania (TiO2) particles were incorporated into the epoxy (EP) matrix to tailor the surface deep trap level. Surface trap parameters, surface conductivity, surface charge density, and surface flashover voltage were calculated and measured. It indicates that surface flashover voltage improves by 23.07% and 14.45% compared to pristine EP when solely introducing MWCNTs or nano-TiO2 particles into the EP matrix, while it increases by 36.04% for C0.1T2 as simultaneously introducing both particles. When adding small amounts of particles, the surface charge transport is suppressed due to the introduction of bonded layers in the interfacial region, and the surface deep trap level is improved. As the surface deep trap level increases, charge transport and electron emission processes in the solid surface layer are hindered, which reduces the surface positive charge density and the distortion of the electric field and further results in the reduction of surface conductivity and the improvement of dc surface flashover voltage in a vacuum. The explanation for the effects of surface deep traps on surface flashover is essential for further improvements of surface flashover. [ABSTRACT FROM AUTHOR]