Influence of parameters of molecular mobility on formation of structure in ferroelectric vinylidene fluoride copolymers
The low-temperature molecular mobility has been studied by dielectric relaxation spectroscopy on the bulk films of statistic copolymers of vinylidene fluoride (VDF) with tetra- (TFE) and trifluoroethylene obtained by crystallization from a solution in acetone. The results show that activation energy of the kinetic units in the glassy state depends significantly on the concentration of polar groups. The cooperative mobility above the glass transition temperature is described by Vogel-Tamman-Fulcher equation; the lowest value of the effective activation energy was found in the copolymer with highest amount of non-polar TFE content. It has been shown that the parameters of the dynamics are related to the structural parameters obtained by infrared spectroscopy, wide-angle X-ray Spectroscopy, and small-angle X-ray scattering. In particular, the largest crystals and the highest value of the “large” period have been detected in VDF/TFE copolymer with lowest activation parameters of microbrownian and local mobility. Number of lamellar crystals in stacks is determined by the concentration of VDF polar groups in copolymer chain.