Some considerations about the analysis of thermostimulated depolarization peaks

Abstract

The dielectric relaxation mode associated with the liquid-glass transition of a fluorinated co-polymer, P(VDF-TRFE) 75/25 mol.%, has been resolved experimentally by the technique of fractional polarizations, and a discrete distribution of relaxation times has been obtained. This distribution shows a compensation pattern characteristic of the glass transition/relaxation of polymers. Attention has been paid to the effect of the experimental set-up on the obtained activation parameters by using polarization windows Delta Tp of 0, 5 and 10 degrees C. It was shown that the activation energy increased as the polarization window was reduced. The latter also had a slight influence on the compensation parameters. This behaviour has been explained in terms of an increase in the width of the distribution of relaxation times associated with elementary peaks as Delta Tp increased. Thus, the Bucci-Fieschi-Guidi (BFG) analysis based on monokinetic relaxations is no longer valid as this distribution broadens. Overall, the use of Delta Tp=5 degrees C as polarization window constituted the best compromise between validity of the BFG analysis and the experimental resolution of the depolarization current. The errors in the compensation temperature have been estimated and a test has been applied in order to reject the hypothesis of a compensation pattern due to a propagation of experimental errors. Thus, the compensation phenomena described true kinetic effects, independently from the experimental set-up. It was shown that data pertaining to different methods of analysis could also describe a compensation law, which was actually statistical in nature.