Electrical conductivity and space charge in LDPE containing TiO2 nanoparticles

Electrical conductivity (DC) and space charge accumulation were studied in samples of low density polyethylene to which nano-sized and micro-sized TiO₂ (anatase) particles and a dispersant had been added. Sample thicknesses were in the range 150-200 μm. At applied field strengths of 10 and 20 kV/mm, the conductivity at 30 °C, measured in vacuum in samples containing 10 % w/w nano-sized TiO₂, decreased by 1-2 orders of magnitude relative to samples with dispersant but without TiO₂, and by three orders of magnitude at 70 °C. In air at 30 °C the corresponding decrease was an order of magnitude at 10 kV/mm, and a factor of four at 20 kV/mm. In samples containing 10 % w/w micro-sized TiO₂ the conductivity increased in air and in vacuum, but only by factors in the range 2-10 depending on temperature and field. Space charge profiles were obtained using the laser-intensity-modulation-method (LIIMM), irradiating both surfaces of the sample. The micro-sized TiO₂ particles are associated with increased charge injection from the electrodes and increased charge trapping in the sample bulk, increasing the conductivity overall. The nano-sized particles generate very little charge in the sample bulk, but render the electrodes partially-blocking and so lower the conductivity.