High β-phase PVDF films formed by uniaxial compression

Polyvinylidene fluoride (PVDF) is a semicrystalline polymer with excellent ferroelectric properties. The β crystal form has the best piezoelectric properties among its five crystal forms. Conventionally, PVDF films with a high β-phase are produced by uniaxial stretching of α-phase PVDF films. Uniaxial compression of α-PVDF samples of thickness 3.2 mm was done to obtain β-PVDF films of thickness about 100μm, with biaxial orientation. The effects of temperature and compression ratio on the compressed PVDF films were studied using Raman spectroscopy, FTIR spectroscopy and cross-polarized optical microscopy. Uniaxial compression of the α-phase PVDF sample resulted in transformation to the β-phase, accompanied by distortion of the originally present Maltese cross structures in the optical micrographs. The compressed samples exhibited β-phase fraction anisotropy along the radial and thickness directions of the sample at lower compression ratios. PVDF samples with about 80% β-phase were obtained for compression ratios more than 12 at temperatures of 60 and 90 °C.