Effect of crystallinity on the dielectric behavior of poly(vinylidene fluoride) in the region of glass transition

The relaxation of PVDF films with various thermomechanical prehistory was s tudied in the region. of glass transition by the dielectric method. The rel axation time of the microscopic Brownian motion in the amorphous phase decr eases abnormally with increasing degree of the polymer crystallinity. This effect is connected to discontinuities in the packing density within disord ered regions caused by the formation of thicker lamellae. The resulting inc rease in the free volume leads to the decrease in relaxation time. For the textured films, the increment of dielectric absorption increases markedly u pon the sample orientation. The results of spectroscopic measurements showe d this to be due to an orientation-induced conformational transition of the type (GG) --> (TT)(n), with the latter isomers having higher transverse co mponent of dipole moment. The thermodynamic analysis based on the temperatu re dependence of the static permittivity suggests the possible formation of regions with a correlated arrangement of the polar segments-quasidomains. The interactions are assumed to have a long-range nature, while the charact er of chain packing in the quasidomains is suggested to be of the nematic t ype.