Electrostatic model of LDPE-SiO2 nanodielectrics

An electrostatic model to explain and predict the dielectric properties of nanocomposites made of low density polyethylene (LDPE) filled with SiO₂ nanoparticles is presented. In the present approach the modeled nanodielectric is a polymer matrix with uniformly distributed identical spherical nanoparticles embedded, each nanoparticle being surrounded by a three-layer interface. Assuming a possible structure of the interface, an estimation of the dipole types and concentrations is made and then the permittivity and charge distribution inside the interface regions are estimated and used in a numerical model based on the finite element method. The computational domain of the 3D numerical model developed for the LDPE-SiO₂ nanodielectric is reduced to an elementary fraction of the whole geometry (a cube containing eight nanoparticles), by taking into account the existing physical symmetries imposed by appropriate boundary conditions. This model is implemented in the finite element method based software package COMSOL Multiphysics for three filler concentrations: 2, 5 and 10 wt%. The results show a good correlation between the effective permittivity calculated with our model and the experimentally measured permittivity and emphasize the influence of the space charge presence inside nanodielectric on the electric field repartition and on the effective permittivity. A comparison between our results and those obtained with other models is also discussed.