The effects of surface ion concentration on interfacial polarization in EPR/clay composites

Recent work at the Electrical Insulation Research Center has been concerned with polarization, dielectric relaxation and space charge accumulation in both polyethylene and filled ethylene-propylene copolymers. Measurements of both thermally stimulated currents (TSDC) and the dielectric constants, ε' and ε", by time domain dielectric spectroscopy (TDDS) have been carried out in these investigations. The TSDC measurements made on polyethylene samples showed that significant space charge could be injected from the electrodes into the polymer at poling fields of 5000 kV/m. In contrast, for poling fields below 2×10⁴ kV/mm the quantity of injected space charge was extremely small in the filled ethylene propylene diene monomer (EPDM) samples. Most of the polarization observed in the EPDM samples was shown to be due to interfacial polarization in samples containing more than 20 phr kaolin clay. This communication reports the results of some measurements on EPDM samples containing kaolin particles whose surfaces have been treated to change the ion concentrations on the surfaces of the kaolin particle