Modelling of dielectric breakdown through charge dynamics for polymer nanocomposites

A dielectric breakdown model consisted of bipolar charge transport and free volume breakdown criterion is used to investigate the dc breakdown properties of polymer nanocomposites. In the model, we consider charge injection from electrodes, carrier migration with a constant mobility, charge trapping and detrapping associated with deep traps, charge recombination, and energy gained for charge carriers from the local distorted electric field. Since incorporating nanoparticles into a polymer can change its density and/or energy of deep traps, we calculate the dielectric breakdown properties of low-density polyethylene nanocomposites characterized by various densities and energies of deep traps. The simulated results show that the breakdown strength increases with an increase in the density and energy of deep traps, which is consistent with the experimental results. It is shown that the accumulation of homocharges, the distortion of electric field, and the energy gain of free carriers are regulated to improve the performance of breakdown.