Various areas of application of thermo-stimulated current (TSC) spectroscopy, used for studying insulating materials, are reviewed. The characteristics of this technique are compared with those of the other thermally stimulated spectroscopies. The origins of TSC are briefly cited. Examples of the identification of TSC peaks with ionic or molecular movements (inorganic or organic materials) are given. >

A review of thermo-stimulated current

Cooperative relaxation modes associated with transitions of various systems have been experimentally resolved into elementary processes characterized by activation enthalpies and entropies following a compensation law. Two transitions with no kinetic effect-solid-solid transition and Curie transition have been studied. In both cases, the corresponding dielectric relaxations are characterized by a compensation phenomenon with transition temperature as the compensation temperature. Dielectric relaxations liberated at the glass transition, T g , have also been studied. They are also associated with a compensation law but, in that case, the compensation temperatures T g + 10/30°. This lag has been attributed to the kinetic character of T g . Note that it is lower in amorphous polymers than in semicrystalline polymers. The distribution function of activation parameters is broader in amorphous polymers than in semicrystalline ones.

Study of cooperative relaxation modes in complex systems by thermally stimulated current spectroscopy

The ac pyroelectric response of a number of differently poled polyvinylidene fluoride films has been measured while the temperature was varied at a constant rate ∼5 °C/min from room temperature to near the melting temperature. The response first increases with increasing temperature, which is attributed to an increase of the thermal expansion coefficient and eventually decreases due to melting and/or loss of electric dipole orientation. The details of the temperature dependence are influenced in a reproducible manner by the poling variables, especially the poling temperature. The measurement is therefore proposed as a way of evaluating the effect of processing variables on the thermal stability of the piezoelectric and pyroelectric properties.

Method of evaluating the thermal stability of the pyroelectric properties of polyvinylidene fluoride: Effects of poling temperature and field

Chapter 15 - Thermally stimulated currents: recent developments in characterization and analysis of polymers

Thermally stimulated current study of relaxation in glassy polycarbonate

Multiple transitions in poly(vinylidene fluoride)-PVF2 - have been studied by thermally stimulated techniques: Thermostimulated creep -TSCr - and thermostimulated current -TSCu -. The resolving power of these methods have allowed us to investigate the fine structure of transitions in PVF2. A relaxation mode is observed around the glass transition temperature -Tg -; it can be described by a distribution of relaxation times following an Arrhenius equation and it has been attributed to microbrownien motions of the amorphous chains. Another relaxation mode is revealed ∼50° higher than Tg. It corresponds to a distribution of relaxation times obeying a Vogel equation and has been assigned to the fluidification of the amorphous chains. In both cases, two sub-modes can be distinguished:The sub-mode observed at lower temperature has been attributed to the amorphous regions free from constraint, while the other one at higher temperature, has been assigned to amorphous chains under constraints from crystall...

Talal El Sayed

Papers

Transitions in poly(vinylidene fluoride) by thermally stimulated techniques