Persistent polarization in poly(vinylidene fluoride). II. Piezoelectricity of poly(vinylidene fluoride) thermoelectrets

Abstract

The piezoelectricity of PVDF thermoelect rets formed with vacuum‐coated aluminum electrodes has been investigated in detail. The piezoelectricity depends on the β‐form crystal structure of PVDF homopolymer and copolymers. However, the piezoelectricity is not attributed to the stress dependence of the spontaneous polarization of β‐form crystals, but rather to the persistent polarization arising from trapped charges. The trapping mechanism is discussed.

Hybrid lead-free polymer-based nanocomposites with improved piezoelectric response for biomedical energy-harvesting applications: A review

“…The poling conditions were as follows: 50 kV cm −1 was applied at 100 °C to PVDF-TrFE containing BTO and rGO [33]. The PVDF poled at 110 °C with an electric field of 50 MV·m −1 exhibited a ten-fold improvement in its d 31 compared to that of the same material poled at 25 °C with an electric field of 30 MV·m −1 [148]. An electric field of 2 kV was applied to an NG made of PVDF and BT NPs, and the electric field was maintained for 8 h [149].…”

Ferroelectric Polymers and Their Energy‐Related Applications

“…The piezoelectric coefficients d ij of ferroelectric fluorinated polymers are strongly dependent on the poling conditions such as the electric field, the temperature, and the poling time, and the difference can be significant with varied poling conditions. For instance, the d 31 of PVDF poled at 110 °C with an electric field of 50 MV m −1 exhibits a 10‐fold improvement to that of the same material poled at 25 °C with an electric field of 30 MV m −1 …”

“…For instance, the d 31 of PVDF poled at 110 °C with an electric fi eld of 50 MV m −1 exhibits a 10-fold improvement to that of the same material poled at 25 °C with an electric fi eld of 30 MV m −1 . [ 134 ]…”

The mystery behind the mid-temperature transition(s) in vinylidenefluoride-based homo-, co- and terpolymers — has the puzzle been solved?

“…The observation of charges and dipoles and their interaction on and in electrets led to the introduction of the concept of hetero-charge (internal space charge and dipole charges; polarity opposite to the polarity of the adjacent electrode) and homo-charge (injected charge; the same polarity as that of the adjacent electrode) [12]. With respect to PVDF, it was proposed that the orientation of dipoles in the crystalline β phase was necessary for piezoelectricitybut only for providing the trapping sites for the charges that caused the polarisation component which leads to piezo-and pyroelectricity [13][14][15] . Today, it is instead accepted that the ferro-, pyro-and piezoelectricity of PVDF and related polymers originate from the polarisation of its ordered crystallites, but also that the amorphous phase around the crystallites and the interface charges at crystalline-amorphous "boundaries" can play significant roles in the piezoelectric response and its stabilisation [16][17][18] .…”