Brillouin Spectroscopic Studies of VF2/TFE Copolymers

Abstract

The temperature dependence of sound velocity was studied in thin sheets of isotropic and oriented copolymers of vinylidene fluoride (81 mol%) and tetrafluoroethylene (19 mol%) by Brillouin scattering. For oriented samples, we studied the differences between the sound velocities along the x-axis (chain direction) and y-axis (perpendicular to x in sample plane). The ferroelectric-paraelectric transition points were not observed because this Tc is very close to the melting point of these copolymers. A partial thermal hysteresis loop was observed for all samples. The transitions from paraelectric phase to ferroelectric phase are completed near 85°C for the isotropic sample and the oriented sample with sound propagating along y. For propagation along x-axis, this transiton is completed at about 100°C which is very close to results from other methods. The behaviors of temperature dependence of sound velocity along x and y axes are quite different, as we observed also in VF2/TrFE copolymers. It allows generalization of our conclusions concerning copolymers of vinylidene fluoride and trifluoroethylene.