Effect of electric field on the infrared spectrum of a ferroelectric poly (vinylidene fluoride-co-hexafluoropropylene) film

We have used infrared spectroscopy to study electric-field induced motions of polymer chains in a ferroelectric uniaxially drawn film of poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] (molar ratio, 1:0.18) consisting mainly of the polar crystalline beta phase. We analyzed the observed spectra under the C-2v symmetry of an infinite poly(vinylidene fluoride) (PVDF) chain. The changes in intensity of the a(1) bands (2979, 1432, 1280, and 842 cm(-1)), b(1) bands (1073 cm(-1)), and b(2) bands (3017, 1168, and 880 cm(-1)) showed butterfly-shaped hysteresis loops characteristic of ferroelectricity when the electric field was varied from 1.4 to 1.4 MV/cm. The changes in intensity of the a(1) and b(2) bands with transition dipole moments perpendicular to the polymer chain were large, whereas those of the b(1) bands with transition dipole moments parallel to the polymer chain were small. The changes in intensity of the a(1) and b(2) bands were mainly attributed to the inversion of the polymer chain around the polymer axis. On the other hand, the changes in intensity of the b(1) band were attributed to the motion of a polar crystallite. (C) 2015 Elsevier B.V. All rights reserved.