Orientation of crystallites in piezoelectric poly(vinylidene fluoride)

The distribution of the orientation of the b and c axes of crystallites in the piezoelectric polymer, poly(vinylidene fluoride), is inferred from the distribution (with varying sample orientation) of diffracted x-ray intensity of the (111) and (001) reflections. Measurements of drawn and poled samples are reported, and results from these measurements as well as those for rolled material are analyzed. The c axes of the crystallites are narrowly distributed about the drawing (or rolling) direction. The b axes are broadly disturbed in the plane perpendicular to the drawing (rolling) direction. The effects of drawing, rolling, poling, and thermal aging upon the distribution of crystallite orientations are discussed. The distribution of dipole orientations and the resulting net polarizations are calculated, using fast Fourier transforms to deconvolve the diffraction data. A model is proposed, for the distribution of the b axes, and is found to fit the data well in most cases. The correlation between the alignment of crystallographic axes and the piezoelectric constants is discussed. Possible improvement in the net polarization of the polymer of a factor of 2 is suggested.