The Effects of Water on the Dielectric Properties of Aluminum-Based Nanocomposites

Abstract

Abstract-A series of polyethylene nanocomposites was prepared utilizing aluminum nitride or alumina nano-powders with comparable morphologies. These were subsequently subjected to different conditioning regimes, namely prolonged storage in vacuum, the ambient laboratory environment or in water. The effect of filler loading and conditioning (i.e. water content) on their morphological and dielectric properties was then examined. Measurements indicated that, in the case of aluminum nitride nanocomposites, none of the conditioning regimes led to significant absorption of water and, as such, neither the dielectric properties nor the DC conductivity varied. Conversely, the alumina nanocomposites were prone to the absorption of an appreciable mass of water, which resulted in them displaying a broad dielectric relaxation, which shifted to higher frequencies, and a higher DC electrical conductivity. We ascribe these different effects to the interfacial surface chemistry present in each system and, in particular, the propensity for hydrogen bonding with water molecules diffusing through the host matrix. Technologically, the use of nanocomposites based upon systems such as aluminum nitride, in place of the commonly used metal oxides (alumina, silica, etc.), eliminates variations in dielectric properties due to absorption of environmental water without resorting to the adoption of techniques such as surface functionalization or calcination in an attempt to render nanoparticle surface chemistry hydrophobic.

The effects of hydration on the DC breakdown strength of polyethylene composites employing oxide and nitride fillers

“…Consequently, any changes in behavior that are observed here are not associated with indirect effects associated with variations in matrix morphology. Rather, the effects we report should be directly related to the presence of the particles themselves [34,35]. In the current investigation, the effects of morphology, conditioning (i.e.…”

“…From the morphological data presented above and from earlier detailed DSC studies [34,35], the inclusion of the various fillers only has a minor influence on matrix morphology and such subtle variations have been shown to have no influence on electrical breakdown strength [32]. However, in all systems, the filler is present in various agglomerated forms but the systems based upon silicon nitride are markedly different from all the others in that they contain no large agglomerates.…”

“…%, plus an unfilled control sample, were prepared from the polyethylene blend and the various particles described above. A modified solvent blending route involving dissolution of the polymer blend in xylene and dispersion of the particles in isopropyl alcohol (IPA) was used throughout [31,34,35]. This approach was adopted here to alleviate difficulties associated with the direct dispersion of polar particles into a non-polar solvent such as xylene.…”

“…immersion in water). Previously [27,34], in systems based upon Si3N4, this process was discussed in terms of the progressive formation of an oxynitride layer, which would be absent in AlNxx [28,35]. Finally, CALxx behaves very differently from SiOxx; it is dry following ambient conditioning and absorbs only a small amount of water even on immersion in water [31].…”

The role of the filler surface chemistry on the dielectric and thermal properties of polypropylene aluminium nitride nanocomposites

“…Thermogravimetric analysis (TGA) data was obtained by heating 5 mg of samples from 100 to 600 °C at a heating rate of 20 °C/min to verify the real loading ratio and from 100 to 900 °C at a heating rate of 10 °C/min to examine the untreated and treated nano-AlN powders. Scanning electron microscopy (SEM) was performed on the film samples treated by an etching procedure described in previous work [19]. The samples were placed on an aluminium slab and gold coated by an Emitech K550X coater.…”