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There is currently no unified theory that explains the role of nanofillers in polymeric insulation. Consequently, different methods such as dielectric spectroscopy analysis are used to understand this role. The existence of a strong interaction between nanoparticles and a polymer is widely accepted. However, the interaction between dipoles has been taken into consideration in Jonscher's Universal Relaxation Law (URL) but not in the Debye theory. Hence, the URL was used in this article as a method to analyze the spectra of epoxy‐ZnO nanocomposites and to try to determine the nanoeffect mechanism. At 160°C above Tg (116°C), the typical phenomenon of low‐frequency dispersion occurs in the epoxy‐ZnO nanocomposites, and with filler loading increased up to 5 wt %, the value of n (calculated from the εr″ spectrum of the nanocomposites) increases both at high and low frequencies. This result indicates that higher loadings correspond to lower dielectric losses changing per radian. Moreover, the decrease in quasi‐direction conduction indicates that the gross dielectric losses of the nanocomposites are also less than pure epoxy resin (EP) at low frequencies. This finding may be attributed to the strong bonding between the nanofillers and the EP, which limits the movement of some macromolecular chains. The URL provides an analytical method for determining the mechanism of the effect of nanofillers on polymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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In this paper, ZnO-Epoxy nanocomposites (NEP) were prepared and epoxy composites that contain 5 wt% microZnO (MEP) and deliberately not well dispersed nano ZnO (NDNEP) were also prepared for purpose of comparison.The effects of the particle size and dispersion of ZnO on dielectric properties of epoxy resin were chiefly studied.Test results showed that: at a loading of 5 wt%, the three epoxy composites seem to have no significant difference onresistivity compared to epoxy resin; Dielectric constants of all the epoxy composites are also basically the same butthey are bigger compared to that of the pure epoxy resin (unfilled); Dielectric dissipation factors (tanδ) of NDNEP isgreater than that of NEP and MEP. NEP has the minimum dielectric loss factor, whereas dielectric loss factors of thethree epoxy composites are larger than that of the pure epoxy resin. The decreasing order of electrical breakdownstrength for the three epoxy composites and for the pure epoxy resin is as follows: NEP>MEP>NDNEP>EP. Finally,in order to explain the experimental results the aggregation interface phase was proposed. Furthermore, addition ofwell dispersed nano filler has proved to have a positive effect on the improvement of the dielectric properties of epoxyresin

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