Dielectric properties of polyimide/boron nitride nanocomposites at high temperature

The high temperature dielectric properties and electrical conductivity of polyimide/boron nitride (PI/BN) nanocomposite films are investigated as a function of the BN nanofiller size. Whereas in such a temperature range (up to 350 °C) the electrical properties of neat PI are controlled by ionic motions, which make it a semi-insulating material, it has been highlighted the important role of the BN nanofiller size on the reduction of the electrode polarization phenomenon and on the low frequency DC conductivity of PI/BN nanocomposites. Particularly with the smallest BN nanoparticle diameters (95 nm and 40 nm), the dielectric properties changes are strongly attenuated above 200 °C and the DC conductivity is decreased by 1 to 3 orders of magnitude compared to neat PI. For higher nanoparticle diameters (120 nm), the effects are less important. It seems possible to extend the high temperature range of use of PI by using adequate small sizes of BN nanoparticles at low filler content.