Thermal hysteresis loop in the elastic incoherent scattering function of vinylidene fluoride and trifluoroethylene ferroelectric copolymers

摘要

A thermal hysteresis loop was measured in the normalized elastic incoherent scattering function F(T,Q) of vinylidene fluoride and trifluoroethylene copolymers during a heating cooling scan across the ferroelectric phase transition. Three vinylidene fluoride copolymers with molar fractions p=0.60, 0.70, and 0.75 were studied. In addition, for the molar fraction 0.70 three crystallinities c=0.35, 0.61, and 0.70 were investigated. The hysteresis loop was interpreted in terms of a dynamical entropy defined by S_d(T,Q) =-R ln[F(T,Q)] that can be factorized as a temperature-dependent entropy factor and a Q dependent form factor with two characteristic lengths λ_1 the control parameter of the entropy and λ_2 the control parameter of the confined volume. The thermal hysteresis loop observed in the entropy is attributed to the change in the confined volume of the dynamic relaxation. The dynamical entropy could be a useful concept for the analysis of the complex dynamic of macromolecular systems such as polymers.