Thermal characterization of a vinylidene fluoride-trifluorethylene (75–25) (%mol) copolymer film

Vinylidene fluoride-trifluorethylene (VDF-TrFe) copolymers – exhibits ferroelectric properties due to the special arrangement of the chain units in the crystalline phase. The co-polymers have attracted intense scientific and technological interest due to the possibility of studying the ferroelectric phase transition, as it occurs before the melting of the material. Being that the piezo- and pyroelectric properties of the material are the most interesting from a practical point of view, they have been intensively studied in the recent years. Nonetheless, there is a lack of information about the thermal behavior of other relevant characteristics of the samples. In this work, P(VDF-TrFE) (75/25) has been characterized by mechanical tests and a series of thermal analysis techniques, including thermal mechanical analysis (TMA) and differential scanning calorimetry (DSC). The films exhibit slight mechanical anisotropy, and in the longitudinal direction larger mechanical properties, due to the higher structural organization. DSC results show two well-defined peaks corresponding to the ferroelectric-paraelectric transition and the melting of the paraelectric phase at higher temperatures. Two relaxation processes were found (β and αc) by dynamic mechanical analysis (DMA). The β 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. At higher temperature, the αc relaxation was related to the thermal variation of the dimensions of the films in the longitudinal direction during heating, recorded by TMA.