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 Thus, the Bucci-Fieschi-Guidi (BFG) analysis based on monokinetic relaxations is no longer valid as this distribution broadens.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.

Influence of internal flexibility on the double glass transition in a series of odd non-symmetric liquid crystal dimers characterised by dielectric measurements

“…The intensity measured by this technique reveals the existence of different kinds of charge relaxations, such as the dipolar α relaxation which is the dielectric manifestation of the glass transition in polar materials. One interesting feature of TSDC is its ability to resolve a distributed process into more elementary contributions [32,33]. An elementary spectrum can be described more accurately in terms of a single relaxation time and can be thus better studied according to existing models.…”

Dielectric and mechanical properties of various species of Madagascan woods

“…TSC measurements were taken with a homemade equipment previously described (Teyssedre and Lacabanne 1995). Samples (square of 15 mm by 15 mm; 0.5 mm thick) were inserted between two steel plate electrodes.…”

“…The depolarization current was normalized to be homogeneous with dipolar conductivity r, and it was recorded with a constant heating rate q h . The series of elementary thermograms was recorded by shifting the poling window by 5°C toward higher temperature (Teyssedre and Lacabanne 1995). In this procedure, each elementary thermogram can be considered as a Debye process characterized by a single relaxation time s(T).…”

Liquid Crystalline Polymers Compatibilization and Adhesion Enhancement by Reactive Blending in Post-Consumers PET’s

“…In order to verify if the LCP and the host polymer underwent some chemical interaction during the reactive extrusion, a very sensitive analytical technique (Teyssedre and Lacabanne, 1995) that measures the depolarization currents of thermally stimulated samples was used. Under an external electrical field the polymer (which is a dielectric medium) accumulates electric charges in a form that can be retained for long time.…”