Degradation of the dielectric and piezoelectric response of β-poly(vinylidene fluoride) after temperature annealing

The effect of annealing temperature and time on the dielectric and piezoelectric response of poly(vinylidene fluoride), PVDF, was studied. The observed decrease in the value of the dielectric, ε′, and piezoelectric, d ₃₃, constants is related to depoling of the material and not to variations of the degree of crystallinity or the electroactive β-phase content. In a general way, the dielectric and piezoelectric responses decrease strongly in the first 4 h at a given temperature, in particular for temperatures higher that 80 °C, reaching stable values for longer annealing times. For most applications, the temperature of 100 °C will set the limit of suitable performance. Nevertheless, the material still retains a stable piezoelectric response of ca. 4 pC/N after reaching temperatures of 140 °C. The mechanisms behind the observed behavior are discussed.