Structural, conformational, and polarization changes of poly(vinylidene fluoride-trifluoroethylene) copolymer induced by high-energy electron irradiation

Structural and molecular conformation changes of high-energy electron-irradiated poly(vinylidene fluoride-trifluoroethylene) 50/50 copolymer have been investigated by means of FT-IR spectroscopy, X-ray diffraction, and cross-linking density measurement and are compared with the change of polarization hysteresis loops with dose. Although in general the irradiation reduces the macroscopic polar ordering, which leads to the eventual disappearance of the remanent polarization in the copolymer at room temperature, the change in the mesoscopic structure and molecular conformation with dose is not monotonic. In the intermediate dose range, there is a reversal of the change of local ordering with dose, as revealed by the decrease of the fraction of the TG conformation in the copolymer and contraction of the lattice in directions perpendicular to the polymer chain with dose, which could be caused by the high cross-linking density due to irradiation. In addition, for irradiated polymers at doses above 30 Mrad, no transition behavior with temperature is observed in the FT-IR spectra, consistent with the early experimental results that the ferroelectric-paraelectric transition has been eliminated by irradiation.