Thermally stimulated depolarization current

A detailed discussion of the statistical thermodynamic aspects of thermally stimulated dielectric relaxation is not provided here. It should suffice to state that kinetics of most of the processes are again complicated and that the phenomenological kinetic theories used to described thermally stimulated currents make use of assumptions that, being necessary to simplify the formalism, may not always be justified. Just as in the general case, TSL and TSC, the spectroscopic information may in principle be available from the measurement of thermally stimulated depolarization current (TSDC). However, it is frequently impossible to extract it unambiguously from such experiments. 

Thermally Stimulated Depolarization Currents in Amorphous Chalcogenides... 

FIGURE 18.11 Thermally stimulated depolarization currents of PVP K30 demonstrating two different global relaxation peaksPi is the (5-relaxation peak (representing molecular motion belfry, and P2 is the a-relaxation peak (representing mobility ). 

Shmeis, R. A., Z. V fong, and S. L. Krill. 2004. A mechanistic investigation of an amorphous pharmaceutical and its solid dispersion, Part I Acornparative analysis by thermally stimulated depolarization current and differential scanning calorimetl harm Re 1 2025-2030. 

G. Gallego Ferrer, M. Monleon Pradas, J. L. Gomez Ribelles, and P. Pissis, Swelling and thermally stimulated depolarization currents in hydrogels formed by interpenetrating polymer networks, J. Non-Cryst. Solids 235-237, 692-696 (1998). 

Thermally stimulated depolarization currents are detected in a sample first cooled to low temperature in a capacitor with shorted electrodes, then warmed slowly with the electrodes connected to a sensitive d.c. electrometer. In this way the dielectric relaxation processes occurring in the sample are displayed separately, according to their activation energies and barrier heights, during the scan over temperature. 

Abbreviations DEA, dielectric analysis >OC. degree of crystallinity DSC, di erential scanning calorimetry LM, local mobility (secondary relaxations) SR, structural relaxation 7g, determination of glass transition temperature TSDC. thermally stimulated depolarization current spectroscopy XRD, X-ray difTractometry. Source Adapted from Ref. 15. 

TSDCT thermally stimulated depolarization current technique... 

Figure 21. Schematic diagram of an apparatus for thermally stimulated depolarization current (TSDC) experiments.

The electrical properties, i.e, volume resistivity, dielectric permittivity and dielectric loss factor, as well as thermally stimulated depolarization current, were measured on polypropylene-polycarbonate (PP-PC) blends. The results confirm the existence of some interactions between the non--compatible components of PP-PC blends. 

TSC is a technique for detecting the transitions that depend on changes in the mobility of molecular scale dipolar structural units. TSC is based on the ability of polar molecules to be moved by an electrostatic field. Two types of current are generated thermally stimulated polarization current (TSPC) and thermally stimulated depolarization current (TSDC). TSPC is generated when dipolar structures orient in a static electric field with increasing in the temperature. TSDC is generated because of the relaxation of the previously polarized molecules as reported in Fig. 5. 

Gun ko, V.M., Turov, V.V., Leboda, R., Zarko, V.I., Skubiszewska-Zi ba, J., and Charmas, B. 2007f. Adsorption, NMR and thermally stimulated depolarization current methods for comparative analysis of heterogeneous solid and soft materials. Langmuir 23 3184—3192. 

Figure 1 Thermally stimulated depolarization current curves in reduced current density units, measured on PP homopolymer samples in a wide temperature range. Wl, reference W2, annealed W3, oxidized (data taken from [3]) Jl, nondrawn film J2, drawn film (data taken from [4]).

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