Effect of the crystallinity on the dielectric properties of polyvinylidene fluoride

The dielectric permittivity of semi crystalline polyvinylidene fluoride (PVDF) in the /spl alpha/ phase, has been studied from 10 to 300 K at frequencies ranging from 10/sup 2/ to 1/spl times/10/sup 5/ 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 /spl alpha//sub 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/sub 0/ and /spl tau//sub 0/. The Williams-Landel-Ferry model was also applied and no deviations near the glass transition temperature were observed. The experimental values of /spl epsi/'' 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.<
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