Effect of electroactive phase transformation on electron structure and dielectric properties of uniaxial stretching poly(vinylidene fluoride) films

The effect of stretching conditions, such as stretching ratios, temperatures and rates of extension, on the relative fraction of beta-phase and electron structure as well as dielectric properties of poly(vinylidene fluoride) (PVDF) films was investigated. The fraction of beta-phase in PVDF film increases greatly and reaches the peak of 93% after uniaxial stretching. Meanwhile, stretched spherulites and micro-strips paralleling with the stretching direction were observed in the matrix by atomic force microscopy (AFM). The results of fine structure of fluorine and carbon elements in PVDF, identified by X-ray absorption near edge structure (XANES), indicate that the coordination between F and H atoms of the adjacent chains is produced and thus enhances the dielectric response of the stretched film. As a result, the dielectric constant of the stretched film increases by 50% and achieves up to 12.1, as well as the dielectric loss being as low as 0.02.