Effect of recrystallization on the molecular mobility of a copolymer of vinylidene fluoride and hexafluoropropylene

Abstract

Relaxation processes in copolymers of vinylidene fluoride with hexafluoropropylene (93/7) were studied by means of a dielectric method. The initial extruded film was recrystallized by free heating to temperatures above the melting point and by subsequent cooling. This increased both the perfection of the crystal phase and the degree of crystallinity. The impact of recrystallization on both the relaxation times (s's) and the activation parameters of the local mobility (b process) and microBrownian cooperative mobility in amorphous phase (a a process) was almost negligible, whereas the s's of the a c relaxation were an order of magnitude higher after recrystallization. Qualitatively, it was predicted by the soliton model for the a c relaxation. The recrystallization affected characteristics of the transition at the highest temperature (a) registered in the region of the melting of the crystals even more. The process is related to the relaxation of the space charge formed by ionogenic impurities, which migrate through the amorphous phase with high free volume. It was shown that the dynamics in the amorphous phase controlled the drift mobility of free charge carriers and, by that, determined the s of the space charge relaxation process. The structuring processes during the recrystallization also affected the parameters of the orderdisorder transition in the low-perfect ferroelectric (antiferroelectric) phase.

Synthesis and Characterization of Core–Double-Shell-Structured PVDF-grafted-BaTiO3/P(VDF-co-HFP) Nanocomposite Films

“…The dielectric permittivity of P(VDF- co -HFP) at temperatures higher than T g , that is, in the temperature range of −20 °C to 40 °C, increases with increasing temperature and decreasing frequency. At room temperature, it amounts to around 8 at 1 kHz ( Figure 6 a), which is consistent with the values known from the literature ( ε ′~10), depending on the HFP content in the P(VDF- co -HFP) copolymer [ 52 , 55 , 56 ]. This permittivity increase is attributed to the enhanced segmental motions of dipole units within P(VDF- co -HFP), associated with both α a and α c relaxation.…”

“…The real part of the dielectric function, or permittivity, ε ′, has a point of inflection at the lowest frequencies, connected to an additional relaxation process, known as α c relaxation. This process is related to relaxation occurring within the crystalline phase of P(VDF- co -HFP), and shows up at temperatures around 0 to 40 °C [ 51 , 52 ].…”

Structural Aspects at Phase Transitions in Ferroelectric Copolymers of Vinylidenefluoride and Tetrafluoroethylene

“…As appears from Figure 7b, annealing in the continuous heating mode to 200 ºС is accompanied by appreciable change of diffraction curves, especially for intramolecular order (larger s). As it is earlier noted on copolymers VDF with hexafluoropropylene (Kochervinskii, 2011), the additional peaks are observed in a film after recrystallization. The changes occur in some structural parameters after the recrystallization in as shown in the table.…”

PVDF‐based dielectric polymers and their applications in electronic materials

“…More recently, Kochervinski et al [99] reported the ferroelectric behaviour of typical P(VDF‐TFE)94/6 mol% copolymers, which is found that the copolymer looks like a linear dielectric whose permittivity nonlinearly increases with the amplitude of the alternating field in low fields, as shown in Fig. 19.…”

“…Changes in the shape of the dielectric-hysteresis loop with variation in the amplitude of the external field of P(VDF-TFE)94/6 mol%[99] Schematic configuration of PVDF sensor[10β] …”