Poling of β-poly(vinylidene fluoride): dielectric and IR spectroscopy studies

Abstract

β-Poly(vinylidene fluoride) (β-PVDF) exhibits ferroelectric properties due to the special arrangement of the chain units in the crystalline phase. The piezoelectric properties of the material can be optimised by poling the original stretched film. The main effect of the poling process is the alignment of the randomly organised dipolar moments against the applied field. In this work, poled and non-poled β-PVDF from the same batch are characterised by dielectric spectroscopy. The origin of the electrical and mechanical response of poled and non-poled β-PVDF were further explored by far IR spectroscopy and discussed on a molecular level. The main effect of the poling process on the dielectric response of the material is a small increase of the dielectric constant due to the preferential alignment of the main dipolar contribution and a slight decrease of the dielectric loss, due to the more organized amorphous structure. The conductivity is strongly increased by poling, especially the high-temperature conductivity, ascribed mainly to hopping conductivity due to free charges induced during poling. FTIR experiments indicate that the origin of these effects and also of the variations in the thermo-mechanical response of the material can be found in the reorientation of the crystalline dipoles along the poling field, together with a partial reduction of the amount of α phase and an increase of the amount of β phase. The α to β transformation, mainly due to the stretching process, seems to be optimized by the poling process.

Characterization of poled and non-poled β-PVDF films using thermal analysis techniques

“…3), it is difficult to correlate the features of this process with the direction and the poling effect. In a previous study, it seemed that the non-poled films exhibit more intense damping properties in the region of the ␣ c -relaxation when tested in the L-direction [11]. However, the present results are not able to confirm such findings.…”

“…In fact, it was demonstrated before with FTIR data that poling films have higher relative contents of ␤-crystals, in comparison with ␣ ones [11]. For the poled sample we have a more oriented structure where the dipolar moments are directed towards a preferential direction.…”

Influence of the processing method on the properties of a PVDF film

“…It is well known that the three PVDF crystalline phases α, β, and γ have the following characteristic absorption bands in the IR-range [13,14]:…”

Effect of interfacial interactions on the electromechanical response of poly(vinylidene fluoride-trifluoroethylene)/BaTiO3 composites and its time dependence after poling

“…The d 33 values were stable in the observed 1-week time for both SC and CM films. As shown in figure 2, the relative permittivity of the P(VDF-TrFE) films increased upon poling, possibly due to the alignment of dipoles in the piezoelectric phase [25], and then slowly decreased with time after poling. The dielectric loss tangent also slightly increased upon poling and then decreased with time.…”