Peculiarities of structure and dielectric relaxation in ferroelectric vinylidene fluoride-tetrafluoroethylene copolymer at different crystallization conditions

Vinylidene fluoride (VDF)/tetrafluoroethylene (TFE) 94/6 copolymer films obtained by low-temperature crystallization from acetone solution and by melt-crystallization under high pressure were studied. As shown in the X-ray diffraction patterns, β- and γ- phases coexist in the sample crystallized from a solution. At melt-crystallization, a number of γ-crystals decrease and spherulitic supramolecular structure is formed. It is accompanied by a decrease of the amorphous phase density in the intra- and inter-spherulite regions, which leads to an increase in the glass transition temperature. Differential scanning calorimetry data indicate a smaller fraction of the amorphous phase for the sample crystallized from the melt. At the same time, the relaxation strength of the mobility in the amorphous phase in this sample is higher. This contradiction is explained by the increased ratio of isomers in planar zigzag conformation, as shown by IR spectroscopy.