Studies on the transformation process of PVDF from α to β phase by stretching

Abstract

Poly(vinylidene fluoride) (PVDF) has excellent pyro-and piezoelectric properties which are related to the bcrystal of PVDF. Most of the b-crystal of PVDF can be transformed from the a-crystal by mechanical stretching. The effects of stretching conditions on the transformation from a to b phase of PVDF were studied in this paper. In addition, changes of crystalline structure of PVDF during the stretching process were observed in situ under an optical tensile stress microscopy tester, and the samples after being stretched were investigated using a 3D digital microscope and an infrared microscope. The results show that stretching temperature (T s ) and drawing ratio (l) are critical to the transformation from a-crystal to b-crystal of PVDF. The T s around 100 C and l above 3 is recommended. The in situ observation indicates that the deformation of crystalline structure began from the middle of a-spherulite and extended to another spherulite, and caused the large-scale transformation. Scanning results of infrared microspectroscopic and 3D digital microscopy revealed that a phase of PVDF would change into b phase with the deformation of the spherulite, and the distribution of the different crystalline phase in PVDF after being stretched was also given. It is believed that this work is instructive and meaningful to studies on phase transformation and production of the piezoelectric film of PVDF.

A rectification-free piezo-supercapacitor with a polyvinylidene fluoride separator and functionalized carbon cloth electrodes

“…The β phase PVDF exhibits remarkably piezoelectric properties 45 . The working mechanism of the piezo-supercapacitor is shown in Figure 5.…”

The influence of crystalline transformation of Ba0.6Sr0.4TiO3 nanofibers/poly(vinylidene fluoride) composites on the energy storage properties by quenched technique

“…It is found that the composite films consisted of α-phase, β-phase PVDF [31]. The β-phase is observed at 840, 878, 1171, and 1232 cm À 1 [24]. The bands at 878 cm À 1 is assigned to the CH 2 and CF 2 groups generated from the CH 2 rocking and CF 2 stretching and the bands at 1171 and 1232 cm À 1 are assigned to the CH 2 group, which is associated to the CH 2 wagging and rocking [22,31].…”

“…PVDF, also a nontoxic material, is a semi-crystalline polymer that exists in three different crystalline forms including the non-polar TGTG' phase (α-PVDF), the polar TTTT phase (β-PVDF), and TTTGTTTG' phase (γ-PVDF). Different crystal phases of the PVDF films were obtained, depending on the preparation conditions like stretching of thin films and quenched conditions [21][22][23][24][25]. The dielectric, piezoelectric and ferroelectric properties of PVDF in different phases especially β-PVDF have been well studied.…”

Improving the dielectric performance of poly(vinylidene fluoride)/polyaniline nanorod composites by stretch‐induced crystal transition

“…There exists a more facile and effective strategy to increase the dielectric constant of polymers by transforming the polymer crystal from non‐polar crystal into polar crystal . The typical polymer is PVDF with two dominating crystals, α‐crystal and β‐crystal . The α‐crystal, belonging to the trans–gauche (TGTG′) conformation, is a non‐polar phase and exhibits a low dielectric constant; it can normally be obtained from the melt by cooling down to room temperature at a regular cooling rate or solvent cast with solvent evaporation .…”