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Moisture is known to influence the electrical performance of polymers. The introduction of nano particulates creates numerous additional pathways which radically affect the migration of moisture in nanocomposite materials. In this paper, cross-linked polyethylene/silica nanocomposites at loadings of 5 wt% and 12.5 wt% of both unfunctionalized and vinylsilanefunctionalized nano silica were exposed to humid environments at elevated temperature. Nanocomposites were found to have a much higher moisture uptake compared to cross-linked polyethylene base resin. The dielectric properties of these hydrothermal conditioned samples were characterized by breakdown strength measurements, pulsed electro-acoustic analysis, and dielectric spectroscopy. A close relationship between particle loading, moisture uptake and dielectric properties was found, which provides important evidence that determining the optimal particle loading of nanodielectrics should take moisture influence into account.

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Ashcraft-type samples have been used to grow vented water trees in crosslinked polyethylene and crosslinked polyethylene based nanocomposites with 5 wt% and 12.5 wt% functionalized silica. Tree growths are reported at a range of stresses by sectioning the samples destructively. A nondestructive method is also introduced which allows visualization of electrochemical trees without sectioning. Nanocomposites are found to have higher resistance to water tree growth and this trend becomes clear with larger loading. Due to the high interface/volume ratio in nanocomposites, it is believed that scattering in the interfacial region inhibits tree growth.