Non‐destructive thermal ageing evaluation of P (VDF‐HFP) film based on broadband dielectric response

Capacitors and sensors based on polymer dielectric materials are key components in electrical systems and electronic devices. Considering the temperature rise during operation, an effective evaluation method for the thermal ageing of polymer matrix is urgently needed. P(VDF-HFP) film with a thickness of 20 mu m is manufactured by solution casting and a thermal ageing experiment up to 1000 h is conducted. Dielectric responses of wide ranges of temperatures and frequencies are measured for samples with different ageing durations. The universal relaxation law and Dissado-Hill dielectric response model are applied to further investigate the results. The characteristics of individual processes are obtained, which demonstrate that the main chain relaxation following the Vogel-Fulcher-Tammann equation and side chain relaxation following the Arrhenius equation both remain unchanged after thermal ageing. However, the activation energies of those two processes change significantly during the process and show different variation trends. The activation energy of the side chain relaxation gets larger monotonically due to the influence of annealing and the breaking of crystalline region. As a result, a non-destructive evaluation method for the thermal ageing of P(VDF-HFP) is proposed accordingly.