Influence of extrusion, stretching and poling on the structural and piezoelectric properties of poly (vinylidene fluoride-hexafluoropropylene) copolymer films

Three types of poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) copolymer films were prepared by extrusion, stretching as well as simultaneously stretching and static electric field poling (SSSEP), respectively, and measured by the differential scanning calorimetric, wide angle X-ray diffraction, fourier transformation infrared-attenuated total reflection, and Dynamic mechanical analysis. The experimental results showed that the films prepared by stretching and SSSEP have higher crystallinity and β phase than by extrusion. SSSEP improved the chain orientation enormously both in crystalline and amorphous regions, resulting in the highest storage modulus. Because of the lower β phase content, the extruded films exhibited the lowest piezoelectric coefficient d 33 . For the stretched and SSSEP films, although the β phase content was similar, the d 33 was distinct because of the different potential energy for the rotation of the dipoles. In addition, the SSSEP films gave the maximum d 33 (24 pC/N), higher than the other PVDF-HFP copolymer films that have been reported.