Dielectric relaxation activation parameters

Samouillan et al. (2011) studied the dielectric properties of elastin at different degrees of hydration and specifically at the limit of freezable water apparition. The quantification of freezable water was performed by DSC. Two dielectric techniques were used to explore the dipolar relaxations of hydrated elastin dynamic dielectric spectroscopy (DDS), performed isothermally with the frequency varying from 10 to 3 x 10 Hz, and the TSDC technique, an isochronal spectrometry running at variable temperature, analogous to a low-frequency spectroscopy (10 to 10 Hz). A complex relaxation map was evidenced by the two techniques. Assignments for the different processes can be proposed by the combination of DDS and TSDC experiments and the determination of the activation parameters of the relaxation times. As already observed for globular proteins, the concept of solvent-slaved protein motions was checked for the fibrillar hydrated elastin (Samouillan et al. 2011). 

In the study of dielectric relaxation, temperature is an important variable, and it is observed that relaxation times decrease as the temperature increases. In Debye s model for the rotational diffusion of dipoles, the temperature dependence of the relaxation is determined by the diffusion constant or microscopic viscosity. For liquid crystals the nematic ordering potential contributes to rotational relaxation, and the temperature dependence of the order parameter influences the retardation factors. If rotational diffusion is an activated process, then it is appropriate to use an Arrhenius equation for the relaxation times ... 

The s parameter following this procedure is found to be between 0.91 and 0.95 and the conductivity increases x 10 x S cm-1. The activation energy, for this conductive process, obtained from the Arrhenius plot was equal to 100.5 kJ mol-1 (1.04 eV). As usual, the dielectric strength of the a -relaxation Ae = eoa — < coa, decreases when the temperature increases. The shape parameter for both parameters are nearly temperature independent. 

The principal characteristics of the triboelectret state in polymers recorded experimentally are i) the efficient surface charge density (ESCD) value and ii) the thermally stimulated depolarization (TSD) current spectrum, i.e. the discharge current dependence of the electret on its heating temperature. The analysis of TSD spectra helped to estimate the parameters of the triboelectret state, including the homo- to heterocharge relation in a dielectric, activation energy of the charge relaxation processes, relaxation time and others. 

Here Ae is the dielectric strength and t the mean relaxation time. The parameters a and P describe the symmetric and asymmetric broadening of the relaxation process. The temperature dependencies of the relaxation times of the observed a-relaxation process for pure PPX, PPX + Cu, and PPX + Zn samples demonstrate an Arrhenius behavior with the energies of activation 196 kJ/mol, 187kJ/mol, and 201kJ/mol, respectively, and correlate with the activation energies of the a-process in most known polymer materials [75]. 

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