Temperature-Dependent Rotational Dipole Mobility and Devitrification of the Rigid Amorphous Fraction in Unpoled and Poled Biaxially Oriented Poly(vinylidene fluoride)

Abstract

In addition to the pronounced ferroelectric property from polar crystalline phases, poly(vinylidene fluoride) (PVDF) and its random copolymers also exhibit high dielectric permittivities as a result of highly mobile dipoles in the amorphous phase. In this study, we developed a new theoretical approach to determine the dipole concentration, dipole moment, dipole−dipole interaction, and rotational dipole mobility for PVDF by means of broadband dielectric spectroscopy. From the permittivity of molten PVDF, the Kirkwood−Froḧlich g-factor and its temperature dependence were determined and used as global parameters for the simulation of unpoled and highly poled biaxially oriented PVDF (BOPVDF). It was found that the concentration of active dipoles substantially increased as the temperature was increased from −30 to 40 °C, indicative of the devitrification of the rigid amorphous fraction (RAF). Both the calculated dipole moment and the g-factor of poled BOPVDF were higher than those of unpoled BOPVDF, resulting in a higher permittivity and piezoelectric performance. In addition, the dipole−dipole interaction was found to increase substantially upon increasing the temperature from −30 to 40 °C, leading to an increase of over 4 orders of magnitude in the rotational dipole mobility. This was direct evidence for the devitrification of the RAF in both unpoled and poled BOPVDF.

Liquid Electrolyte-Assisted Electrospinning for Boosting Piezoelectricity of Poly (vinylidene Fluoride) Fiber Mats

“…As shown in Figure c, the improved piezoelectric output caused by a decreasing temperature of the liquid electrolyte medium may come from two aspects. For one thing, low temperature increases the crystallinity and β phase content of PVDF fiber mats due to the ion-dipole interaction and phase separation of PVDF solution. ,− For another, the inhibition of PVDF dipole relaxation or even further polarization of dipoles is realized due to the freeze of PVDF macromolecular chain conformation by low-temperature phase separation, as well as the local ion–dipole interaction. , …”

“…8,81−83 For another, the inhibition of PVDF dipole relaxation or even further polarization of dipoles is realized due to the freeze of PVDF macromolecular chain conformation by low-temperature phase separation, as well as the local ion−dipole interaction. 84,85 Interestingly, the V OC of the P15S20T0 fiber mat under 20 N is about 2.3 V (Figure 5e), which is 7.7 times and 1.8 times of the PVDF fibers collected by aluminum foil (0.3 V) and salt solution (1.3 V), respectively. In addition, the piezoelectric output voltage of the P15S20T0 fiber mat reaches 3.5 V at 40 N impact force, which is superior to other electrospun PVDF films using conventional fiber collection mediums.…”

Fold Surfaces of Polymer Crystals Are Nucleation Sites: The Link between Polymer Decoration, Secondary Crystallization, and the Rigid Amorphous Fraction (RAF)

“…It also justifies the introduction of a new subclass of "Mobile Oriented Amorphous Fraction" (MOAF), by Zhu et al that emphasizes its differences with the standard views about the RAF and MAF. 59 Along the same line, similar interpretations have resulted from, to quote, "simple NMR experiments" performed on polyethylenes of different molecular architectures (linear, short, and long branches, UHMWPE). 60 Four components can be resolved and quantified.…”

“…This “dynamic conformational disorder” associated with “long-range positional and orientational order” is illustrated by recent results reported on PVF2 materials by Zhu et al They observe a “substantial increase in rotational dipole mobility” (by four orders of magnitude) from −30 to 40 °C [NB: the bulk T g is at −45.2 °C, and the secondary and primary crystals melt at 55.1 and 175.5 °C, respectively]. It also justifies the introduction of a new subclass of “Mobile Oriented Amorphous Fraction” (MOAF), by Zhu et al that emphasizes its differences with the standard views about the RAF and MAF …”

Directional freezing-induced self-poled piezoelectric nylon 11 aerogels as high-performance mechanical energy harvesters

“…Previous studies demonstrated that for oriented samples both crystalline and amorphous orientation can simultaneously contribute to the output performance. 15,65,66 To conrm that the electrical output signals detected were, in fact, the piezoelectric outputs of the nanogenerator device, we monitored the outputs of the nanogenerator under a reverse connection to the external circuit (Fig. S12 †).…”