Dielectric relaxation in nanocrystalline polymers

Dielectric properties of the nanocrystalline polymers such as polyvinylidenefluoride have been investigated with and without nanofilleres (i.e. BaTiO₃ nanoparticles) at frequency ranges from 100 Hz to 1 MHz range in the temperature range from 30 to 150°c. The increase in permittivity with temperature may be due increase in molecular mobility and also may be partly due to the expansions of lattice sites by incorporation of nanoparticles. The crystalline-amorphous interface in PVDF and PVDF nanocomposites act as a trapping centers for carriers. The increase in losses at higher frequency could be associated with the polarization of the trapped charge carriers. The decrease in losses at lower frequencies seems to show the number of charges and delay in settling of dipole due to availability of very short time in one half cycle of altering voltage. The AC conductivity, first increase with frequency up to about 800 kHz and, thereafter, dielectric loss and AC conductivity decreases with frequencies. The decrease in the permittivity and increase in the dielectric loss and AC conductivity are attributed to the fact the random (thermal) orientations of segments. In present case the dielectric loss is small in lower frequency side but it is increasing toward higher frequency side.