Functionalization of Silica Nanoparticles to Improve Crosslinking Degree, Insulation Performance and Space Charge Characteristics of UV-initiated XLPE

Innovative approaches for augmenting dielectric properties in cross-linked polyethylene (XLPE): A review

Throughout the history of power systems, power cables have been used to securely and efficiently distribute electrical energy to the destined locations. Cross-linked polyethylene (XLPE), a commonly used insulator in high-voltage cables, have several desirable properties, such as low dielectric loss, high dielectric constant, high thermal conductivity, enhanced thermal stability, and superior resistance against electrical stress. However, further improvements of XLPE's performance are needed. The incorporation of large specific surface area nanoparticles, such as boron nitride nanosheets and graphene oxide, exhibited a great potential in enhancing XLPE's properties. These nanoparticles create numerous trapping sites, even at small loading levels, due to their large interfacial regions. In addition, voltage stabilisers with polar groups can scavenge high-energy electrons generated by local electric fields, thereby inhibiting the electrical tree growth. Another important aspect of enhancing XLPE's dielectric performance is the inclusion of antioxidants with phenolic groups. These antioxidants react with peroxyl radicals, mitigating their harmful effects. This review summarises the effects of nanoparticles, voltage stabilisers, antioxidants, and polymer amalgamation on dielectric performance of XLPE as an insulation material. The major challenges in dielectric insulation such as breakdown voltage strength, electrical tree growth, structural defect, space charge accumulation, and thermal aging are addressed.

Advances in Polymer Dielectrics with High Energy Storage Performance by Designing Electric Charge Trap Structures

Dielectric capacitors have been developed for nearly a century, and all-polymer film capacitors are currently the most popular. Much effort has been devoted to studying polymer dielectric capacitors and improving their capacitive performance, but their high conductivity and capacitance losses under high electric fields or elevated temperatures are still significant challenges. Although many review articles have reported various strategies to address these problems, to the best of current knowledge, no review article has summarized the recent progress in the high-energy storage performance of polymer-based dielectric films with electric charge trap structures. Therefore, this paper first reviews the charge trap characterization methods for polymeric dielectrics and discusses their strengths and weaknesses. The research progress on the design of charge trap structures in polymer dielectric films, including molecular chain optimization, organic doping, blending modification, inorganic doping, multilayered structures, and the mechanisms of the charge trap-induced enhancement of the capacitive performance of polymers are systematically reviewed. Finally, a summary and outlook on the fundamental theory of charge trap regulation, performance characterization, numerical calculations, and engineering applications are presented. This review provides a valuable reference for improving the insulation and energy storage performance of dielectric capacitive films.

Bionic ordered structured hydrogels: structure types, design strategies, optimization mechanism of mechanical properties and applications

Natural organisms, such as lobsters, lotus, and humans, exhibit exceptional mechanical properties due to their ordered structures. However, traditional hydrogels have limitations in their mechanical and physical properties due to their disordered molecular structures when compared with natural organisms. Therefore, inspired by nature and the properties of hydrogels similar to those of biological soft tissues, researchers are increasingly focusing on how to investigate bionic ordered structured hydrogels and render them as bioengineering soft materials with unique mechanical properties. In this paper, we systematically introduce the various structure types, design strategies, and optimization mechanisms used to enhance the strength, toughness, and anti-fatigue properties of bionic ordered structured hydrogels in recent years. We further review the potential applications of bionic ordered structured hydrogels in various fields, including sensors, bioremediation materials, actuators, and impact-resistant materials. Finally, we summarize the challenges and future development prospects of bionic ordered structured hydrogels in preparation and applications.

Dielectric Characteristics of Crosslinked Polyethylene Modified by Grafting Polar-Group Molecules

Polar group-modified crosslinked polyethylene (XLPE) materials are developed with a peroxide thermochemical method of individually grafting chloroacetic acid allyl ester (CAAE) and maleic anhydride (MAH) to polyethylene molecular-chains, which are dedicated to ameliorating dielectric characteristics through charge-trapping mechanism. By free radical addition reactions, the CAAE and MAH molecules are successfully grafted to polyethylene molecular chains of XLPE in crosslinking process, as verified by infrared spectroscopy molecular characterizations. Dielectric spectra, electric conductance, and dielectric breakdown strength are tested to evaluate the improved dielectric performances. Charge trap characteristics are investigated by analyzing thermal stimulation depolarization currents in combination with first-principles electronic-structure calculations to reveal the polar-group introduced mechanisms of contributing dipole dielectric polarization, impeding electric conduction, and promoting electrical breakdown field. The grafted polar-group molecules, especially for MAH, can introduce deep-level charge traps in XLPE materials to effectively restrict charge injections and hinder charge carrier transports, which accounts for the significant improvements in electric resistance and dielectric breakdown strength.

The synthesis and characterization of polyorganosiloxane nanoparticles from 3-mercaptopropyltrimethoxysilane for preparation of nanocomposite films via photoinitiated thiol-ene polymerization

This article describes the synthesis of modified silica nanoparticles (SiO₂-MPTMS) via the condensation reaction carried out between silanol moieties of silica nanoparticles and the trialkoxy silyl groups of (3-mercaptopropyl) trimethoxysilane (MPTMS). Then, SiO₂-MPTMS nanoparticles in certain amounts (0.5 wt %, 1 wt %, 2.5 wt % and 5 wt %) were incorporated into thiol-ene resins consisting of bisphenol A glycerolate dimethacrylate and trimethylolpropane tris(3-mercaptopropionate) to prepare nanocomposite films via the photoinitiated thiol-ene polymerization in presence of 2,2-Dimethoxy-2-phenylacetophenone 99% as a photoinitiator. Fourier transform infrared spectroscopy, dynamic light scattering, scanning transmission electron microscopy, thermal gravimetric analyzer, and X-ray photoelectron spectrometer were employed to characterize SiO₂-MPTMS nanoparticles. It was revealed that the nanosilica surface was successfully grafted by MPTMS with the grafting ratio of 22.9%. Properties of the nanocomposite films such as decomposition temperature, thermal glass transition temperature, tensile strength, hardness, and particle distribution were investigated and the results were compared with each other and neat film. The addition of MPTMS-modified silica particles did not improve the thermal stability of the films. In scanning electron microscopy study, it was seen that 2.5 wt % of these nanoparticles used as additives were about 200 nm in size and dispersed homogeneously in the polymer matrix. The increase in tensile strength of nanocomposite films compared to the neat film was measured as 77.3% maximum.