Combined dielectric spectroscopy and thermally stimulated currents studies of the secondary relaxation process in amorphous poly(ethylene terephthalate)

Abstract

ABSTRACT:The dielectric secondary ␤ relaxation process of poly(ethylene terephthalate) has been investigated by dielectric spectroscopy (DS) and thermally stimulated currents (TSC). To analyze the broad and asymmetric DS spectra, without previous assumptions on the shape and the number of overlapped loss components constituting the ␤ relaxation, a description in terms of a distribution of relaxation times (DRT) has been used. The Tikhonov regularization method has been used to extract the DRT from DS data. At lower frequency, the TSC technique revealed two components in the ␤ relaxation process. The TSC spectra are experimentally resolved into elementary Debye processes by using the fractional polarization method. A set of elementary relaxation times with relaxation strength ⌬ i as statistical weight of TSC-DRT have been calculated. The temperature shifts of the DRT obtained from both dielectric techniques are analyzed. Whereas the maximum and the lower time wing of the DRT obtained from DS correspond to the ␤ 2 process resolved by TSC and associated to the noncooperative motions of carbonyl groups, the upper time wing of DRT extracted from DS is in accordance with the ␤ 1 process resolved by TSC and assigned to the cooperative motions of phenyl rings.

Secondary Retardation/Relaxation Processes in Bisphenol A Polycarbonate: Thermostimulated Creep and Dynamic Mechanical Analysis Combined Investigations

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Dielectric study of the molecular mobility and the isothermal crystallization kinetics of an amorphous pharmaceutical drug substance

“…The low temperature position and the Arrhenius temperature dependence of β a ‐relaxation are characteristic of a secondary dielectric relaxation mode. This relaxation has been attributed to localized intramolecular mobility of SSR molecules on the basis of comparisons with that which has been demonstrated for amorphous and semicrystalline polymers 13,15–17,29,30. As for polymer materials, the β a ‐relaxation process corresponds to the oscillation of small dipolar groups exhibiting relative high dipolar moments.…”

“…Contrary to the dynamics of species implied in secondary β a ‐relaxations, which obey Arrhenius behavior over the entire frequency–temperature range probed by TSC and DDS,15 a change in the dynamics of molecular motions involved in the main α a ‐relaxation process of amorphous SSR was noted at T g (Fig. 12).…”

“…By shifting the position of the polarization window along the temperature axis, in steps of 2.5°C, the mobility of all sets of species with different dynamics can be analyzed. Further details regarding the TSC‐FP method are available in the literature 15,18,29,30…”

Dielectric and optical properties of a poly(ethylene terephthalate) membrane in the temperature interval 150–400 K

“…The obtained value of E a was approximately 0.52 ± 0.04 eV. This value was lower than the corresponding values of PET foils from the literature, which were 0.71 and 0.83 eV, respectively. On the other hand, the obtained value was similar to values obtained for the porous fibrous polyethylene terephthalate structure presented in ref.…”