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-irrad iated poly-(vinylidene fluoride-trifluoroethylene) 50/50 copolymer have bee n investigated by means of PT-IR spectroscopy, X-ray diffraction, and cross -linking density measurement and are compared with the change of polarizati on hysteresis loops with dose. Although in general the irradiation reduces the macroscopic polar ordering, which leads to the eventual disappearance o f the remanent polarization in the copolymer at room temperature, the chang e in the mesoscopic structure and molecular conformation with dose is not m onotonic. 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 o f the TG conformation in the copolymer and contraction of the lattice in di rections perpendicular to the polymer chain with dose, which could be cause d by the high cross-linking density due to irradiation. In addition, for ir radiated polymers at doses above 30 Mrad, no transition behavior with tempe rature is observed in the FT-IR spectra, consistent with the early experime ntal results that the ferroelectric-paraelectric transition has been elimin ated by irradiation.