Time-resolved, stress-induced, and anisotropic phase transformation of a piezoelectric polymer

We investigate the time-dependent and anisotropic phase transformation of poly (vinylidene difluoride) (PVDF) under bending. Using combined techniques of an atomic force microscope and a Fourier transform infrared spectroscope, observation of surface morphology and phase transformation in time was made. Results showed that bending stress induces the transformation of amorphous, alpha,beta, and gamma crystalline phases. Specifically, the amorphous phase was transformed into the beta phase when the bending force was applied. In addition, the transformation observed was time and direction dependent. The anisotropic behavior observed brings insights into the origin of the piezoelectricity of PVDF.