The γ → β phase-transition behavior of polyvinylidene fluoride under uniaxial drawing

Abstract

β polyvinylidene fluoride (PVDF) has aroused heated discussion in recent years due to its use in piezoelectric and ferroelectric materials. A traditional method to obtain β-PVDF is stretching α-PVDF at an appropriate temperature. The γ phase possesses very similar chain conformation to that of the β phase, so obtaining the β phase via the γ phase is valuable. In the present work, a pure γ-PVDF film of a single component was obtained via self-nucleation technology. For comparison, a pure α-PVDF film was prepared through a melt-recrystallization process. The phase transition of γ to β and α to β in a stretching process was monitored in situ. Stretching at 110 °C showed the best efficiency of obtaining the β phase for both samples. Phase transformation began at a much lower strain for γ-PVDF than for α-PVDF. For γ-PVDF, β crystals appeared before the orientation of γ crystals in the early-plastic region. In contrast, for α-PVDF, the orientation of α crystals occurred before formation of β crystals. The different transition mechanisms of γ to β and α to β may have been caused by the different conformation and stress of γ- and α-PVDF. This work shines light on the phase-transition mechanism of PVDF under uniaxial drawing, and provides an uncomplicated method to obtain β-PVDF.