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Space charge distributions were investigated in two-layer dielectric films consisting of certain combinations of low-density polyethylene (LDPE) and its nanocomposite with magnesia nanofillers at de electric fields of 25 kV/mm and 100 kV/mm at room temperature. Space charge is formed at the interface of two different materials to maintain the continuity of current when the electric field is 25 kV/mm, while packet-like charge appears only in the LDPE at 100 kVImm. These phenomena are explained by assuming that the nanofillers effectively suppress the increase in conductivity induced by the high electric field. Related work done previously by the authors is also briefly reviewed.

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SUMMARYPolymer nanocomposites are attracting attention as emerging insulating materials. We measured the thermally stimulated depolarization current (TSDC) in low-density polyethylene (LDPE)/MgO nanocomposites while varying measuring such parameters as the temperature increase rate and the intensity of the applied electric field. A TSDC peak that spreads over a wide temperature range from 0 °C to 60°C was observed in all samples. As the amount of MgO nanofiller increases, the TSDC peak height decreases. Furthermore, by adopting a partial heating method, the wide TSDC peak was resolved into several component peaks. Among them, the peak at about 12 °C was found not to appear in the base LDPE. Analysis of its initial rising portion indicated that the 12 °C peak had a fairly large energy depth of about 2 eV. These results indicate that charge carriers tend to be captured more strongly after the addition of MgO nanofillers. If these captured charge carriers induce homocharge layers in the vicinity of the electrodes, further space charge formation would be suppressed. This seems to explain the fact that the amount of space charge is smaller in nanocomposites with a proper addition of MgO than in the base LDPE. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(3): 1-7, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com).