Sublinear dispersive conductivity in polyetherimides by the electric modulus formalism

TL;DR

This study investigates space charge relaxation in polyetherimides using electric modulus formalism, revealing sublinear conductivity behavior due to correlated ion hopping and thermal activation effects.

Contribution

It applies electric modulus analysis to polyetherimides, demonstrating sublinear dispersive conductivity and modeling the temperature dependence of relaxation parameters.

Findings

Sublinear power-law conductivity observed in polyetherimides.

Identification of thermally activated parameters and deep traps.

Correlation of ionic motion decreases with temperature.

Abstract

It can be seen by Dynamic Electrical Analysis that the electrical properties of polyetherimide at temperatures above the glass transition are strongly influenced by space charge. We have studied space charge relaxation in two commercial grades of polyetherimide, Ultem 1000 and Ultem 5000, using this technique. The electric modulus formalism has been used to interpret their conductive properties. In both grades of polyetherimide, asymmetric Argand plots are observed, which are related to a sublinear power-law dependency ($\omega^{n}$ with $n<1$) in the real part of the conductivity. This behaviour is attributed to correlated ion hopping. The imaginary part of the electric modulus exhibits a peak in the low frequency range associated to conduction. Modelling of this peak allows us to obtain the dependence, among other parameters, of the conductivity ($\sigma_0$), the fractional exponent ($n$) and the crossover frequency ($\omega_\mathrm{p}$) on the temperature. The $\alpha$ relaxation, that appears at higher frequencies, has also to be modelled since it overlaps the conductivity relaxation. The study of the parameters in terms of the temperature allows us to identify the ones that are thermally activated. The difference between the conductivity relaxation time and the Maxwell relaxation time indicates the presence of deep traps. The coupling model points out that the correlation of the ionic motion diminishes with temperature, probably due to increasing disorder due to thermal agitation.