Metal particle pollutants inside gas-insulated metal enclosed switchgear (GIS) equipment can cause severe electric field distortion, leading to surface discharge of insulators. This paper proposed a method of dielectrically functionally gradient insulator for suppressing metal particles. The electric field distribution around the basin insulator and the motion characteristics of metal particles were simulated. The results show that metal particles released from the shell are affected by the axial electric field force and tend to move towards the insulator. The permittivity distribution of the laminated functionally gradient (ε_L-FGM) insulator decreases in the radial direction, which can homogenize the electric field distribution along the insulator surface and drive away the metal particles by reversing the electric force with the axial electric field. However, the ε_L-FGM insulator enhances the electric field on the surface of the shell, and the jump height of metal particle is 2.7 times higher than those around the uniform insulator. Compared with ε_L-FGM insulator, the ε_T-FGM insulator with a spatial permittivity gradient, which designed based on the topology optimization, reduces the jump height of metal particles and performs better effect in regulating the electric field and expelling the particles.

In order to improve the weak dispersion of two-dimensional nanosheets in polymer matrix and improve the electrical performance of composite materials, a two-dimensional micron expanded layer molybdenum disulfide (E-MoS₂) was prepared by hydrothermal method, and then polyimide (PI) based super-large lattice molybdenum disulfide nanosheets (PI/E-MoS₂) composite films were prepared by in-situ polymerization method. The surface/cross section structure of the composite films was observed by scanning electron microscopy (SEM), the molecular valence bond composition of the composite film was analyzed by Fourier infrared spectroscopy (FTIR), and the phase structure of the composite film was analyzed by X-ray diffraction (XRD). Furthermore, the dielectric constant, DC electrical conductivity, and dielectric loss factor of the composite films were tested, and the effect mechanism of extended lattice on the breakdown and polarization behavior of composite films was studied. The results show that when a small amount of E-MoS₂ nanosheets is added into PI film, there is little agglomeration phenomenon on the surface of PI/E-MoS₂ films, and there is little obvious holes and a small number of structural defects on the cross section, which indicates a good compatibility between fillers and matrix. The incorporation of E-MoS₂ nanosheets can enhance the interfacial polarization of the composite films, improve both the dielectric constant and electric field strength, and decrease the dielectric loss.

In order to investigate the improving mechanism of polysiloxane with different substituents on atomic oxygen (AO) erosion resistance of polyimide in space environments, reactive molecular dynamics (MD) simulations was used to analyze the AO erosion resistance of PI composited with polyhedral oligomeric silsesquioxane (POSS) with trifluoromethyl (-CF₃) group and methyl (-CH₃) group. The results show that both the composites exhibit strong AO erosion resistance by forming an SiO₂ layer that blocks AO propagation into the polymer matrix and and heat transfer. The PI/CF₃-POSS shows the best performance, and its normalized mass is 0.83 after 35 ps of AO exposure, while the nomalized mass of the PI/CH₃-POSS composite is 0.78.

Three fluoro-containing polyimide (PI) resins (PI-II_a, PI-II_b, and PI-II_c) were prepared by two-step chemical imidization procedure using a fluoro-containing dianhydride 9,9-bis(trifluoromethyl)xanthene-2,3,6,7-tetracarboxylic dianhydride (6FCDA, II) and three kinds of aromatic diamines, including 2,2ʹ-bis(trifluoromethyl)-4,4ʹ-diaminodiphenylether (6FODA, a), 1,4-bis[(4-amino-2-trifluoromethyl)phenoxy]benzene (6FAPB, b) and 2,2-bis[(4-aminophenoxy) benzene]propane (BAPP, c), respectively. For comparison, the referenced PI resins (PI-I_a, PI-I_b, and PI-I_c) were prepared with the same procedure except that 6FCDA was replaced by 4,4ʹ-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). And then six kinds of PI films were prepared by high temperature curing process, and their properties were studied. The results show that the solubility of PI-II_a, PI-II_b, and PI-II_c resins in organic solvents is lower than that of PI-I_a, PI-I_b, and PI-I_c resins. Compared with PI-I_a, PI-I_b, and PI-I_c films, PI-II_a, PI-II_b, and PI-II_c films show higher glass transition temperature (T_g), lower linear coefficient of thermal expansion (CTE), little lower optical transparency, and relatively higher dielectric constant (D_k). The PI-II_a film has the optimal comprehensive properties, its T_g and CTE is 362.5℃ and 39.6×10^-6 K^-1, respectively, its optical transmittances at the wavelength of 450 nm (T₄₅₀) is 83.9%, and the D_k at the frequency of 10 GHz is 3.00.

The insulation status of the cable intermediate joint plays an important role in the safe and stable operation of cable. In view of the immaturity of terahertz imaging technology and the limitation of finite element analysis method, an ultrasonic signal characterization method for typical internal defects of silicone rubber in cable accessories was proposed in this paper. At first, different types of typical defect in silicone rubber were designed by simulation. Then the time-domain characteristic quantity and correlation analysis were carried out on the reflected echoes received in the ultrasonic detection simulation, and the correlation coefficient between the time-domain waveform characteristic quantity and the size and angle of defects was obtained. Finally, an ultrasonic test platform was built on the basis of pulse echo method to carry out ultrasonic test on the flat silicone rubber samples with defects. The results show that the size and angle of the internal defects of silicone rubber have a good correlation with the amplitude peak of the first echo, and the detection results of crack defects are more affected by the angle than that of bubble defects, and the amplitude peaks of defects at different angles are significantly different. It is concluded that the ultrasonic signal can effectively characterize the typical internal defects of silicone rubber in cable accessories.

With the constant updating of flexible display devices, the researches on colorless transparent polyimide (CPI) films as substrate materials have attracted considerable attention. In order to solve the inherent contradictions among optical performance, high-temperature resistance, dimensional stability, and mechanical properties of CPI, we synthesized a series of semi-aromatic CIP films with side chains containing benzimidazole by copolymerization using cyclobutanetetracarboxylic dianhydride (CBDA) as the dianhydride monomer, 2,2′-bis(trifluoromethyl)-4-diaminobiphenyl (TFMB) and 2-(3,5-diaminophenyl)-benzimidazole (BBIA) as diamine monomers. The influence of hydrogen bonding, free volume, and main chain structure on the properties of films was systematically investigated by the Materials Studio software simulation and experimental results. The results show that the prepared CPI films have excellent optical transparency, thermal resistance, and mechanical properties. The average transmittance of CPI films in wave length of 380-780 nm is higher than 85%, the glass transition temperature (T_g) is above 400℃, the linear coefficient of thermal expansion (CTE) is 15×10^-6-17×10^-6 K^-1, the maximum tensile strength is 165 MPa, and the modulus is in the range of 3.7-5.2 GPa.

This paper introduced the research and application progress on green solvents in the preparation of polyimide from the views of the classification, manufacturing procedures, solvent composition of polyimide films, and the application status of green solvents. Emphatically, the current research status of biobased solvents, including γ-valerolactone (GVL), dimethyl isosorbide (DMI), and dihydrolevoglucosenone (Cyrene^TM) and their applications on the preparation of PI films were presented. The future developing trends of the applications of green solvents in the manufacturing of PI films were prospected.

Photosensitive polyimide (PSPI) is a kind of high-performance polyimide with special structures, which is widely used in semiconductor packaging, integrated circuits, optical display, and other fields due to its excellent heat resistance, mechanical properties, insulating properties, and lithographic processability. In this paper, the PSPI patents applied in China were taken as object, the overall situation of these patents, including changes in the number of patent applications, applicants, and their source countries was analyzed systematically. Especially, the patent applicants inside and outside China and the patent subject distribution since 2011 were discussed. The difference of patent technology and protection priorities of enterprise applicants inside and outside China was compared in detail. The patent technology characteristics and development trends of PSPI were explored.

Polyimide films with high porosity were prepared using 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-diamino-2,2′-dimethyl-biphenyl (mTB) as monomers. During the preparation process, pore-forming agent was added into the system, and the high-temperature thermal imidization of polyamide acid was controlled by the principle of thermo-induced phase separation. The micropore morphology, mechanical properties, and dielectric properties of the films were analyzed. The results show that the porosity of porous films reach 50%-60%. Under the frequency of 10 GHz, the dielectric constant and the dielectric loss factor of the sample PI-1-250-4 h is 2.14 and 0.002 8, respectively, while maintaining good mechanical properties and heat resistance. Due to the introduction of rigid biphenyl building blocks, the porous film still maintains a low coefficient of thermal expansion. The adhesive-free double-sided copper clad laminate, which prepared by combining the porous film with thermoplastic polyimide (TPI) and then pressing copper foil at high temperature, has good interface adhesion and solder resistance, and can apply to high-frequency and high-speed flexible copper clad laminates.

The new environmentally friendly insulating medium C₄F₇N gas mixture will decompose under long-term overheating and partial discharge conditions, and some of the decomposition products will not only affect the stable operation of gas-insulated switchgear, but also cause personal safety hazards. Therefore, the internal of equipment need equip with adsorption materials to adsorb the decomposition products. Molecular sieves, with wide variety and ionic modification space, are regarded as the most promising adsorbent materials for the treatment of C₄F₇N decomposition products. In this paper, the adsorption isotherms and adsorption sites of 11 kinds of pure silica-type molecular sieves (three kinds with cage structure characteristics and eight kinds with pore structure characteristics) on C₄F₇N and its decomposition products were investigated by molecular dynamics calculations. Then the adsorption energy, electron transfer, and density of states parameters of ZSM molecular sieves modified by the cation (H⁺, Na⁺, Mn²⁺, and Fe²⁺) on C₄F₇N and its decomposition products were obtained based on density functional theory (DFT). The molecular dynamics results reveal that the molecular sieve topology and the window size between gas molecules and molecular sieve are important factors affecting the adsorption process. The density functional calculations show that the modification of Mn²⁺ and Fe²⁺ ions could effectively enhance the adsorption effect of ZSM molecular sieves on the decomposition products of C₄F₇N, and the adsorption process is chemisorption. During the adsorption, the main action site of C₄F₇N is C≡N bond, the main action site of C₂F₆ is C=C double bond and F atom, and the main action site of C₃F₈, C₂F₆, and CF₄ is F atom.