Temperature effect on the infrared absorption of ferroelectric copolymer poly(vinylidene fluoride‐trifluoroethylene)

Abstract

AbstractThe intensity of two infrared absorption bands of annealed ferroelectric copolymers [poly(vinylidene fluoride‐trifluoroethylene)] in the mid‐infrared high‐frequency region was found to be strongly related to the annealing temperature. The vibration modes in the amorphous phase of the copolymers were considered to account for these two bands. On the other hand, the temperature dependence of the absorption spectra of the copolymers in the heating and cooling cycle was investigated. In the vicinity of the Curie transition, the absorption bands associated with the CH2 vibrations exhibited a shift in frequency. Two bands were identified as shifting to a high frequency, and one band shifted to a low frequency with heating. These three bands were restored to their room‐temperature frequency with cooling. In addition, copolymers of a higher vinylidene fluoride content exhibited a more pronounced thermal hysteresis in terms of a shift in frequency. This was consistent with the electrical behavior of the copolymers. The trends of the frequency shifts suggested that dipole–dipole coupling existed between two adjacent chains in the all‐trans conformation, which originated from the interaction of the CH2 and CF2 dipoles. The coupling diminished as the copolymers underwent a change in phase above the transition temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1662–1666, 2005