CORRELATION BETWEEN DIPOLAR TSDC AND AC DIELECTRIC-SPECTROSCOPY AT THE PVDF GLASS-TRANSITION

The alpha(a)-mode (associated to the dynamic glass transition) in PVDF -alpha has been studied by Thermally Stimulated Depolarization Current s (TSDC) and Dielectric Spectroscopy (DS) techniques. The distribution of relaxation parameters, reorientation energies, characteristic temp erature, and preexponential factors of the Vogel-Tammann-Fulcher relax ation times have been precisely determined by using the Simulated Anne aling Direct Signal Analysis applied to a partially discharged TSDC al pha(a) peak. This distribution has been used to predict the variation of the dielectric loss, epsilon''(omega, T), in the temperature and fr equency range where the DS measurements were made on the same material . The simulated epsilon''(T, omega) for various omega, are compared to the experimental values. The width of the peak is always too low, due to the restricted distribution used for the generation of the curves. A. relaxation map including the TSDC results is used to determine the relaxation time variation. In the limited frequency range where the A C DS experiments are performed (10(2) less than or equal to f less tha n or equal to 10(5) Hz) a master curve is drawn and the exponents of t he frequency dependence are found at low and high frequency; also, a f itting to the Havriliak-Negami distribution is successfully performed. (C) 1997 John Wiley & Sons, Inc.