Dielectric Characterization of a Thermotropic Liquid Crystalline Copolyesteramide:  1. Relaxation Peak Assignment

Abstract

Dielectric relaxation analysis was carried out on the main chain thermotropic liquid crystalline copolyesteramide Vectra B950. The dielectric spectra of Vectra B950 show four relaxations, instead of three as cited in the literature. These correspond, from high to low temperature, to the glass transition, the rotation of hydroxynaphthoic acid moieties, the rotation of terephthalic acid moieties, and the combined rotation of terephthalic acid and aminophenol moieties. The combination of TSD and DMA analysis made it possible to distinguish between dipole and charge relaxations. Although the TSD and the dielectric results compare well for the low-temperature dipole relaxations, they are not directly comparable for the α relaxation. TSD experiments reveal that free charges have a significant influence on the α relaxation.

Broadband Dielectric Spectroscopy: A Powerful Tool for the Determination of Charge Transfer Mechanisms in Ion Conductors

“…For all the empirical equations, the peak maximum is shifted by varying the relaxation time t. A decrease in t results in an increase in the peak frequency. When using either the Cole-Davidson or the Havriliak-Negami equation, a correction must be made to the relaxation times to account for a shift in the peak position that occurs when the shape parameters are not one [57][58][59].…”

Kinetics of phase transitions and dielectric relaxations in poly-bis(trifluorethoxy- phosphazene) (PBFP)

“…9, where logτ is plotted against the reciprocal temperature). The occurrence of such an extreme can be related with the rate of temperature change [19]. Supposing that this minimum corresponds to a fixed transition stage, the Kissinger analysis is applied in the present case (see Table 5).…”

Dielectric studies of chain dynamics in homogeneous semi-interpenetrating polymer networks

“…The results in Table I do not provide, in particular, any evidence that free charges contribute to the TSDC ␣ peak, 46 which might explain the differences in timescale indicated by the Arrhenius plots ( Fig. 3 and 5).…”

“…First, it has been argued that TSDC and DRS are not directly comparable to the ␣ relaxation because of the contribution of free charges to the TSDC ␣ peak. 46 We consider this point later on the basis of values for the dielectric relaxation strength provided by the two techniques. Second, having calculated the thermodynamic parameters of the ␣ relaxation (Table II), we can now calculate the equivalent frequency of the TSDC measurements: 46…”