Influence of film stretching on crystalline phases and dielectric properties of a 70/30 mol% poly(vinylidenefluoride-tetrafluoroethylene) copolymer

Abstract

Polyvinylidene fluoride (PVDF)-based copolymers with tetrafluoroethylene (P(VDF-TFE)), trifluoroethylene (P(VDF-TrFE)) or hexafluoropropylene (P(VDF-HFP)) are of strong interest due to the underlying fundamental mechanisms and the potential ferro-, pyro- and piezo-electrical applications. Their flexibility and their adaptability to various shapes are advantageous in comparison to inorganic ferroelectrics. Here, we study the influence of stretching temperature on the crystalline phases and the dielectric properties in P(VDF-TFE) films by means of Dielectric Relaxation Spectroscopy (DRS), Fourier-Transform InfraRed spectroscopy (FTIR), Wide-Angle X-ray Diffraction (WAXD), Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). Especially, the effect of stretching and the influence of the temperature of stretching on the mid-temperature ([Formula: see text]) transition are studied in detail. The results show that stretching has a similar effect as that on PVDF, and we observe an increase in the fraction of ferroelectric [Formula: see text]-phase with a simultaneous increment in both melting point ([Formula: see text]) and crystallinity ([Formula: see text]) of the copolymer. While an increase in the stretching temperature does not have a profound impact on the amount of ferroelectric phase, the stability of the ferroelectric phase seems to improve — as seen in the reduction of the Full Width at Half Maximum (FWHM) of the WAXD peaks in both parallel and perpendicular directions to the molecular chain axis. The observation is also supported by the reduction of dissipation losses with an increase in stretching temperature — as seen in DRS measurements. Finally, both stretching itself and the temperature of stretching affect the various molecular processes taking place in the temperature range of the [Formula: see text] transition.

Tuning the Relaxor–Ferroelectric Properties of Poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) Terpolymer Films by Means of Thermally Induced Micro- and Nanostructures

“…Strong effects of the proposed thermal treatments are also seen in the midtemperature transition ( T mid ). This transition usually shows up in the temperature range between 35 and 80 °C in DSC measurements on all VDF-based polymers; its origins were not clear until recently. ,, In the past, different explanations have been proposed to describe the T mid transition including (1) a second glass transition that takes place at a higher temperature than the conventional glass transition, (2) melting of secondary crystals formed as a result of aging, and (3) a conformational disorder (condis) relaxation process that is assumed to lead to flipping of the fluorine atoms in the TG + TG – chains from up to down or vice versa ( TG + TG – → G + TG – T ) . It is to be noted that the observation of a midtemperature process and the corresponding debate on its possible origin can be extended to several semicrystalline polymers including polyethylene, poly­( l -lactic acid), etc. − …”

“…34 It is to be noted that the observation of a midtemperature process and the corresponding debate on its possible origin can be extended to several semicrystalline polymers 35 including polyethylene, poly(L-lactic acid), etc. 35−37 As discussed in our recent publications, 20,23,30,31 on the basis of the existing literature and additional experiments, a new hypothesis has been proposed in which multiple origins behind T mid are considered (only briefly explained here): When samples are heated from lower temperatures through their glasstransition temperature, the molecular chains in the amorphous regions (i.e., those found inside a more or less continuous amorphous phase) become flexible and can thus undergo molecular motions. However, amorphous chains at the amorphous−crystalline (a−c) interphase (such as tie, cilia molecules, and loops) that are constrained between crystallites remain frozen at this temperature.…”

“…The completely annealed sample shows In our previous publication, 43 we indicated that the dual T g peak found in TSDC scans of the terpolymer with a slightly different composition arises from the different monomer units of the terpolymer, similar to the situation of an immiscible polymer blend which also shows multiple glass transitions, while other authors have associated the same peak with different processes taking place in the midtemperature region of PVDF homo-and P(VDF−TrFE) copolymers. 25,44−48 In view of the latest detailed studies on various VDF-based homo-, co-, and terpolymers, 20,30,31 it has become widely accepted that the onset of the midtemperature transition(s) can be attributed to unfreezing of the constrained amorphous phase (CAP), sometimes also referred to as the rigid amorphous fraction (RAF). On the basis of this explanation, the peak found above 0 °C in Figure 9 is most likely related to the T g,u transition in the terpolymer.…”

Microstructures and dielectric properties of fluorene polyester ternary nanocomposites optimized by zero‐dimensional and two‐dimensional fillers

“…For dielectric constant, common polymer materials generally do not have excellent performance, such as polyimide (PI), which has ε r between 3 and 5, and polyvinylidene fluoride (PVDF), which has ε r about 10.0. 22 Polyacrylonitrile (PAN), which has ε r of 6.5, polyvinyl chloride (PVC), which has a ε r of about 3.5, and polyethylene (PE), which has a ε r of only 2.3. At the same time, the E b of polymer materials are also not brilliant enough, such as PI has E b of nearly 300 kV/mm and PVDF also about 300 kV/mm.…”

“…However, due to the defects of low dielectric constant (), short corona‐resistant lifetime and relatively low breakdown strength (), the application of polymers in many fields is restricted. For dielectric constant, common polymer materials generally do not have excellent performance, such as polyimide (PI), which has between 3 and 5, and polyvinylidene fluoride (PVDF), which has about 10.0 22 . Polyacrylonitrile (PAN), which has of 6.5, polyvinyl chloride (PVC), which has a of about 3.5, and polyethylene (PE), which has a of only 2.3.…”