Annealing effects of phase I poly(vinylidene fluoride)

Abstract

AbstractThe effects of annealing temperatures on stretched poly(vinylidene fluoride) film were systematically studied from the “as‐received” condition up to the melting range (180°C). X‐ray diffraction studies indicate that the annealing process brings about better chain packing and increased crystallite perfection. The elastic modulus and piezoelectric strain and stress constants, d3, and e31, decrease as the annealing temperature Ta increases up to 160°C, while the remanent polarization Pr remains almost constant. Some of these characteritics may be interpreted in terms of a morphological transformation of microfibrils. The values of Pr, d31, and e31 increase dramatically as Ta increases from 160 to 180°C; Pr increases from 56 to 85 mC/m2, d31 from 20.2 to 27.7 pC/N, and e31 from 51.4 to 65.2 mC/m2. As a result, the values of Pr and d31 were the largest recorded from any of the samples used in the present study. e31 showed a value close to the largest one; this usually occurs in unannealed samples. Samples annealed in the melting range also exhibit significantly improved ageing characteristics. The large value of Pr and the small relaxation strength of both the dielectric constant and elastic modulus indicates that the largest crystallinity obtained is approximately 70%.