Variations in the Ferroelectricity and Piezoelectricity of Poly(vinylidene fluoride) Accompanying the Phase Transformation

In this study, the method of coating the surface of α-PVDF films with varying fractions of [BMIM]BF4 is employed to introduce ion-dipole interaction forces, thereby triggering a solid–solid phase transition to form γ′-PVDF. Furthermore, a detailed investigation was conducted on the effect of the phase transition from α to γ′ on molecular relaxation and ferroelectric, piezoelectric, and dielectric properties. The study revealed that increasing the mass of [BMIM]BF4 coated on the surface of α-PVDF films could improve the phase transition. However, excessive [BMIM]BF4 was found to disrupt the surface morphology of the PVDF films. Conversely, limiting the mass of [BMIM]BF4 applied to the surface facilitated the preservation of an intact surface for γ′-PVDF. Subsequent DMA studies indicated that the phase transition could enhance the interface between the amorphous and the crystalline phases. Achieving the phase transition from α to γ′ allows PVDF to shift from a state of relaxed ferroelectric material to a ferroelectric material, and it also plays a role in elevating piezoelectric performance. Additionally, the ferroelectric and dielectric characteristics show a correlation with the crystallization temperature. As the crystallization temperature decreases, both Pmax and the dielectric constant exhibit an increase.