The gamma -> beta phase-transition behavior of polyvinylidene fluoride under uniaxial drawing

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