Ftir and DSC Studies of Mechanically Deformed Β-PVDF Films

Abstract

Films of semicrystalline poly(vinylidene fluoride) (PVDF) in the βphase were studied by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The main goal of this study was to improve the understanding of the structural changes that occur in β-PVDF during a mechanical deformation process. FTIR spectroscopy was used to examine the structural variations as a function of strain. DSC data allowed measurement of the melting temperatures and enthalpies of the material before and after deformation, providing information about the changes in the crystalline fraction. After the molecular vibrations were assigned to the corresponding vibrational modes, we investigated the energy and intensity variations of these vibrations at different deformations. A reorientation of the chains from perpendicular to parallel to the stress direction was observed to occur in the plastic region. During the deformation, a decrease in the degree of crystallinity of the material was observed, but the thickness of the lamellae did not change significantly.

Atomistic modelling of processes involved in poling of PVDF

“…The dependence of these bands with the degree of crystallinity and/or external fields such as strain [8][9][10] or temperature [11] allows to monitor possible variations of the chain conformations, orientations and the amount of and phases of the material under the effect of these external fields.…”

“…The vibrational spectrum of -PVDF has been thoroughly investigated and several absorption bands characteristic of the different bonds, the -and -phases and the head-to-head and tail-totail defects of the polymer have been identified [8][9][10][11]. In particular, vibrational bands at 530 cm -1 (CF 2 bending), 615 and 766 cm -1 (CF 2 bending and skeletal bending) and 795 cm -1 (CH 2 rocking) are identified with the -phase.…”

Exclusive self-aligned β-phase PVDF films with abnormal piezoelectric coefficient prepared via phase inversion

“…The appearance of bands at 760, 796, 975, 1210, 1383 and 1423 cm -1 are ascribed to the formation of the α-phase; [11] while peaks observed at 840 and 1234 cm -1 have been ascribed to the formation of β-phase crystallites. [11,26] The absorbance spectra of the films differs significantly from the starting PVDF pellets (not shown here) which consist of primarily α-phase. As shown in Figure 2d, with the decrease in the quenching temperature, a reduction in the peak at 760 cm -1 associated with the α-phase can be clearly observed, which is accompanied by an enhancement in the peak at 840 cm -1 associated with the β-phase crystallites.…”

“…with the further shoulder observed between 175 and 180C being attributed to the γ-phase. [26] In Figure 2c, areas corresponding to each of the α, β and γ phases have been marked out.Sample quenched at 100C clearly shows that the thermogram is largely enclosed within the range of 170-175ºC, corresponding to the dominant α-phase. Similarly, for samples quenched at lower temperatures (TQ<40 o C), a clear shift of the melting peak towards the lower temperature, corresponding to the dominant β-phase can be observed.…”

“…The films quenched at - with the further shoulder observed between 175 and 180C being attributed to the γ-phase. [26] In Figure 2c, areas corresponding to each of the α, β and γ phases have been marked out.…”