Effect of the crystallinity on the dielectric properties of polyvinylidene fluoride

The dielectric permittivity of semi crystalline polyvinylidene fluoride (PVDF) in the α phase, has been studied from 10 to 300 K at frequencies ranging from 10² to 1×10⁵ Hz. The degree of crystallinity was varied from 50 to 60% by using different casting procedures and its value determined by Differential Scanning Calorimetry. The α_a relaxation corresponding to the glass transition of the amorphous PVDF is intense and its maximum shifts from 241 to 273 K as the frequency and the crystallinity vary. The Vogel-Fulcher equation was used to model the dependence of the relaxation time on temperature and to calculate the activation energy, T ₀ and τ₀. The Williams-Landel-Ferry model was also applied and no deviations near the glass transition temperature were observed. The experimental values of ε´´ as a function of frequency and for several temperatures were used to obtain the Universal Dielectric Response of the material. It is shown that the spectral shape parameters are m=0.58 and n=0.80 for the normalized plot