Dependence of ferroelectric switching time of PVDF on mechanical stress and on blending

We report on the ferroelectric switching times τ_s in polyvinylidene fluoride (PVDF), blended with polymethylmethacrylate, subjected to a mechanical stress σ₂ in the transverse direction, and also with the use of different electrode materials. In contrast to theoretical predictions, τ_s does not depend on σ₂, which indicates that the importance of the pseudo-hexagonal crystallography of the crystalline β-modification of PVDF has been overestimated. The saturation polarization decreases severely with decreasing PVDF content whereas τ_s stays constant. Finally, the injection of space charges is of minor importance for both the ferroelectric switching and the attainable polarization, since these do not depend on the electrode material. We conclude that the internal field is not influenced by blending but that this treatment reduces the amorphous phase contribution to the polarization. The dynamics and the strength of the polarization of PVDF can be understood only if the contributions of the orientation correlations and of the dynamics of the polymer chains in the crystal-amorphous interphase to the overall polarization are taken into account in this semi-crystalline material