Characterization of poled and non-poled β-PVDF films using thermal analysis techniques

Abstract

Abstract␤-poly(vinylidene fluoride)-␤-PVDF-exhibits ferroelectric properties due to the special arrangement of the chain units in the crystalline phase. The ferroelectric phase can be optimised by poling the original stretched film, that tends to align the randomly organised crystallites against the applied field. In this work, polarised and non-polarised ␤-PVDF from the same batch are characterised by mechanical tests and a series of thermal analysis techniques, including DMA, TMA and DSC. The films exhibit mechanical anisotropy, and in the longitudinal direction the poled film presents larger mechanical properties, due to the higher structural organisation. Poled and non-poled show similar crystallinity levels but the melting temperature probed by DSC is higher for the non-poled film; for both films the melting peak exhibits a complex shape, indicating a heterogeneous crystalline organization. Two relaxation processes were found (␤ and ␣ c ) by dynamic mechanical analysis (DMA). The ␤ process, attributed to segmental motions in the amorphous phase, appears at the same temperature in both directions, but its intensity was found to be higher for the films tested in the longitudinal direction. For a given direction, the poled films exhibit lower peaks, due to the more organised amorphous structure. At higher temperature, the ␣ c -relaxation was related to the contraction of the films in the longitudinal direction during heating, recorded by thermal mechanical analysis (TMA). The onset of molecular mobility within the crystalline phase allows for cooperative diffusion processes in the amorphous phase, generating the randomisation of the initially oriented structure.

Effect of the degree of porosity on the performance of poly(vinylidene fluoride-trifluoroethylene)/poly(ethylene oxide) blend membranes for lithium-ion battery separators

“…where ΔH f is the melting enthalpy of the sample and ΔH 100 is the melting enthalpy for a 100% crystalline sample, being 103.4 J.g -1 for P(VDF-TrFE) [31] and 203 J.g -1 for PEO [32].…”

Effect of silane coupling agent on the morphology, structure, and properties of poly(vinylidene fluoride–trifluoroethylene)/BaTiO3 composites

“…Generally, the tanδ curves of P(VDF-TrFE) show three transitions in the temperature range explored, before the melting point. At the lower temperature, the β-relaxation peak is usually attributed to segmental motions in the amorphous phase (glass transition) [43][44][45], although recently some authors proposed a contribution by domain walls and defects in crystalline phase [46,47]. In the region between 0 °C and 100 °C a second relaxation process appears, indicated as α-relaxation, the nature of which has not been fully clarified yet [48][49][50].…”

High-temperature property of flexible polyvinylidene fluoride/(Na_0.5K_0.5)NbO₃ vibration energy harvester

“…Thus, the degradation of the d 33 values for the 4-3 harvester of PVDF/NKN above 210°C was caused by the depolarization of NKN particles. V. Sencadas et al 25) reported that the melting point (T m ) of poled and non-poled ¢-PVDF were 156.3 and 160.1°C, respectively. The T m of PVDF is decided according to the crystalline phase and poled condition, and flexible fabric layer having a large specific surface area is sensitive to heat.…”

“…PVDF is suitable for the high-temperature environment because it is one of the super engineering plastics, and it has good heat resistance properties (the melting point: 150170°C). 24), 25) We measured the electric power-output of the PVEHs by the customdesigned apparatus. Furthermore, the d 33 values of the heattreated harvester were measured to determine the depolarization temperature (T d ) of NKN particles, and the relationship between electric power-output and the T d was also investigated.…”

“…30), 31) This relaxation induces some mobility within the chains that may initiate the loosing of molecular orientation. 25) Thus, the decrease tendency of Young's modulus of the 4-3 lamination were related to the property of polymer material. In terms of the temperature dependency of the electric poweroutput, the 4-3 harvester of PVDF/NKN showed the decrease tendency from 80°C.…”