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 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 P phase content, the extruded films exhibited the lowest piezoelectric coefficient d(33). For the stretched and SSSEP films, although the P 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. (c) 2007 Wiley Periodicals, Inc.