Microstructure and Electrical Properties of Fluorene Polyester Based Nanocomposite Dielectrics

As a new type of dielectric material, the low dielectric constant and corona resistance life of fluorene polyester (FPE) restricts the range of its applications. In order to simultaneously achieve a high dielectric constant and the long corona aging lifetime of FPE, SiO2 nanoparticles were chosen as additive to prepare FPE-based composite films. The microstructure of the composite film was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and small-angle X-ray scattering (SAXS). The dielectric performances of the composites, including the dielectric constant, breakdown strength and corona resistance lifetime, were investigated. The results show that the introduced SiO2 does not destroy the structure of the FPE molecular chain and that it increases the thickness of the filler-matrix interface. The dielectric constant of SiO2/FPE composites increased from 3.54 to 7.30 at 1 Hz. Importantly, the corona resistance lifetime increased by about 12 times compared with the pure FPE matrix. In brief, this work shows what possibilities there might be when considering the potential applications of high-strength insulating materials.

The Research of Interface Microdomain and Corona-Resistance Characteristics of Micro-Nano-ZnO/LDPE

In this article, the melting blend was used to prepare the Micro-ZnO/LDPE, Nano-ZnO/LDPE and Micro-Nano-ZnO/LDPE with different inorganic particles contents. The effect of Micro-ZnO and Nano-ZnO particles doping on interface microdomain and corona-resistance breakdown characteristics of LDPE composite could be explored. Based on the energy transfer and heat exchange theory of energetic electrons, the inner electrons energy transfer model of different ZnO/LDPE composites was built. Besides, the microstructure and crystalline morphology of inorganic ZnO-particles and polymer composites were detected by SEM, XRD, FTIR, PLM and DSC test, and the AC breakdown and corona-resistance breakdown characteristics of composites could be explored. From the experimental results, the Nano-ZnO particles after surface modification dispersed uniformly in LDPE matrix, and the nanoparticles agglomeration almost disappeared. The inorganic particles doping acted as the heterogeneous nucleation agent, which improved the crystallization rate and crystallinity of polymer composites effectively. The ZnO particles with different size doping constituted the different interface structure and crystalline morphology, which made different influence on composites macroscopic properties. When the Nano-ZnO particle size was 40nm and the mass fraction was 3%, the breakdown field strength of Nano-ZnO/LPDE was the highest and 15.8% higher than which of pure LDPE. At the same time, the shape parameter β of Micro-Nano-composite was the largest. It illustrated the microparticles doping reduced the probability of nanoparticles agglomeration in matrix. Besides, both Micro-ZnO and Micro-Nano-ZnO particles doping could improve the ability of corona corrosion resistance of LDPE in varying degrees. The corona-resistant breakdown time order of four samples was as follows: LDPE < Micro-ZnO/LDPE < Nano-ZnO/LDPE < Micro-Nano-ZnO/LDPE. When the mass fraction of Micro-ZnO and Nano-ZnO particles was 2% and 3% respectively, the corrosion depth and area of Micro-Nano-ZnO/LDPE was the least, and the ability of corona corrosion resistance was the strongest.

Fabrication, Morphology and Properties of Polyimide/Al2O3 Nanocomposite Films via Surface Modification and Ion-Exchange Technique

Polyimide films with Al2O3composite layers were prepared by KOH solution surface hydrolysis, ion exchange and heat treatment. Scanning electron microscope (SEM), atomic force microscopy (AFM), X-ray diffractometry (XRD), thermo gravimetric analyzer (TGA), breakdown voltage tester, high frequency pulse voltage machine were performed to characterize the micromorphology, thermal stability, mechanical properties, electric breakdown strength, and corona resistance time of composite films. Results indicated that the thermal properties of the composite film are better than the original film. The corona resistance time of the composite film was longer than that of the pristine film. The composite film had the longest corona resistance time and reached 101.2min while the KOH treatment time was 90min.

Facile preparation of multifunctionalisable ‘stealth’ upconverting nanoparticles for biomedical applications

Hide and Seek. Alendronate-modified upconverting nanoparticles display high colloidal stability, protein corona resistance, bright upconversion luminescence (800 nm excitation), and contain multifunctionalisation sites.

Effects of interface bonding on the corona resistance of the polyimide/nano-Al2O3 three-layer composite films

Polyimides (PIs) are widely used in many fields including aerospace and microelectronics. Due to their poor corona resistance, their practical applications were limited, especially in the field of variable frequency motors. In this study, we have achieved for the first time to increase the corona resistance by controlling the preparation process of the three-layered PI composite. A series of PI/nano-Al2O3 composite films with novel three-layer structure were prepared by in situ polymerization employing pyromellitic dianhydride and 4,4-diaminodiphenyl as raw material, N, N-dimethylacetamide as solvent, and doping of nano-Al2O3. The first layer of the PI/Al2O3 composite film was characterized by Fourier transform infrared spectroscopy, and the imidization rate under different processes was calculated. The interface structures and bonding conditions of the composite films were characterized by scanning electron microscope, and the surface morphologies of the composite films treated by different corona-resistance times were investigated. X-ray diffraction analysis was also used to study the effect of nano-Al2O3 on PIs with different imidization ratios. The corona-resistance time and breakdown field strength of the composite films prepared by different processes were also tested. The results indicated that the combination of the three-layer composite film and the corona-resistance abilities of the composite membrane surface was enhanced by increasing the imidization rate. Meanwhile, the corona-resistance time and the electrical breakdown strength of composite films were also improved by increasing the imidization rate.