Direct measurement of the electrocaloric effect in poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) terpolymer films
Résumé
We investigated the entropy change in poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)) films in the temperature range between -5 degrees C and 60 degrees C by direct heat flux calorimetry using Peltier cell heat flux sensors. At the electric field E = 50 MVm(-1) the isothermal entropy change attains a maximum of vertical bar Delta s vertical bar = 4.2 Jkg(-1) K-1 at 31 degrees C with an adiabatic temperature change Delta T-ad = 1.1 K. At temperatures below the maximum, in the range from 25 degrees C to -5 degrees C, the entropy change vertical bar Delta s vertical bar rapidly decreases and the unipolar P vs E relationship becomes hysteretic. This phenomenon is interpreted as the fact that the fluctuations of the polar segments of the polymer chain, responsible for the electrocaloric effect ECE in the polymer, becomes progressively frozen below the relaxor transition.