Crystallization kinetics, polymorphism fine tuning, and rigid amorphous fraction of poly(vinylidene fluoride) blends

Abstract

Fast scanning calorimetry (FSC) is used to study crystallization of poly(vinylidene fluoride) (PVDF), and its blends with a random fluorinated copolymer (FCP) of poly(methyl methacrylate) and 1H,1H,2H,2H‐perfluorodecyl methacrylate (PMMA‐r‐PFDMA). By varying the residence time at isothermal melt crystallization temperatures TMC = 80–120°C, the amount of α‐ and β‐phase can be controlled, yielding partial or complete suppression of β‐phase for all blends studied. Nonisothermal crystallization kinetics are also studied by FSC and analyzed using the Mo model. Crystallization rates increase when FCP is present. PVDF crystallizes into β‐phase when cooled from the melt at rates faster than 3000 K/s giving PVDF crystal fractions of about 0.05–0.16. Only α‐phase occurs at cooling rates slower than 2000 K/s yielding larger PVDF crystal fractions of about 0.30–0.43. Cooling rates between those limits result in mixed α‐ and β‐phase. The rigid amorphous fraction (RAF) of PVDF varies with α and β crystal fraction in PVDF/FCP blends. RAF of α‐phase PVDF ranges from 0.21 to 0.28 whereas RAF of β‐phase PVDF spans a wider range, reaching values from 0.42 to 0.46.

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

“…When eq is used for m d , similar results are obtained; see Figure S1 in the Supporting Information. As temperature increased, n ( T ) increased linearly [that is, β > 0, as seen in eq ], which could be explained by the continuous devitrification of the rigid amorphous fraction (RAF) in BOPVDF. − Note that near T g , a significant portion of the OAF became the RAF, as reported before …”

“…First, using ultrafast DSC, Schick and co-workers determined the RAF content to be around 0.35 at T g , assuming a low x c of 0.25 . Second, Govinna also determined the RAF content for α PVDF to be 0.21–0.28 using conventional TMDSC . However, no report exists for the devitrification of the RAF during heating above T g .…”

The Domain and Structural Characteristics of Ferroelectric Copolymers Based on Vinylidene Fluoride Copolymer with Tetrafluoroethylene Composition (94/6)

“…Such features of the microstructure lead to the fact that the mechanism of piezoelectricity in the considered examples does not coincide with that in inorganic ferroelectrics [1][2][3]7,8]. According to the conclusions of these works, the main contribution to the piezoresponse mechanism is provided by electrostriction [21] and the so-called "size effect", determined by high values of dielectric susceptibility and mechanical compliance due to the presence of an amorphous phase.…”

“…Considering that the ferroelectric domains in the material form β-phase crystals [ 5 , 6 ], in this paper, the hypothesis is considered according to which the chains of the amorphous phase that also participate in the formation of domains can be distinguished. This phase includes the chains of rigid amorphous phase [ 7 , 8 ]. The authors of [ 9 ] investigated copolymers of VDF in various states using NMR and rotation at a magic angle.…”