| In order to find an appropriate cable dielectric material, nanodielectrics consisting of silica particles in cross-linked polyethylene (XLPE) have been formulated using melt-mixing. Various types of chemical modifications were provided to the surface of the nanoparticles in order to understand the mechanism of the particle-polymer interface and to tailor the properties of overall composites. The particulates and the composites formulated have been characterized utilizing several techniques such as electron paramagnetic resonance, Fourier transformed infra-red spectroscopy, x-ray photoelectron spectroscopy, nuclear magnetic resonance, and microscopy.;These nanomaterials were examined for their electrical attributes, and substantial improvement in electrical voltage endurance was demonstrated. In addition significant improvements in electric strength were measured and other physical properties important to the processing and application of cable dielectrics were not sacrificed. It was established that the interfacial charge build-up that is a common feature of micro-filled material is absent in nanodielectrics, and there was also a reduction in over all permittivity of the nanocomposite below that of the base resin.;To understand the mechanism involved in the improvement in the dielectric properties, the chemistry and physics of the particle-polymer interface was crucial. Therefore, some electrical characterizations of the composite materials were performed to find the trap-site separation, trap depth, mobility of the charge carriers, threshold field for internal charge accumulations etc. The chain scission mechanism proposed by Artbauer via free volume theory was extended to the interfacial defects in the composites; the size of such defects being significantly different for the nano- versus micro-composites. The defects resulted in a microcomposite with very low electric strength, and mitigation of the defects via chemical linkage between particle and polymer improved the overall dielectric strength of the nanocomposite. The field at which electron injection occurred was delayed by the surface-treatment provided to the nanoparticles. Particularly the improvement of electric strength for the nano-filled material with polar modifiers was found to be due to charge trapping. For the untreated nano-filled material the charge build-up is absent simply through the leakage via overlapping of conductive interfaces. |
