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

In this study, the method of coating the surface of alpha-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 gamma '-PVDF. Furthermore, a detailed investigation was conducted on the effect of the phase transition from alpha to gamma ' on molecular relaxation and ferroelectric, piezoelectric, and dielectric properties. The study revealed that increasing the mass of [BMIM]BF4 coated on the surface of alpha-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 gamma '-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 alpha to gamma ' 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 P-max and the dielectric constant exhibit an increase.