Sublinear dispersive conductivity in polyetherimides by the electric modulus formalism

Two commercially available polyetherimides, Ultem 1000 and Ultem 5000, have been studied by means of Dynamic Electrical Analysis. Results show that at temperatures above the glass transition dielectric response is highly influenced by space charge. Obtained data is analyzed using the electric modulus formalism. The real part of the conductivity is conveniently described by a sublinear power law dependency (ωⁿ with n<;1), as Argand plots reveal, associated with correlated hopping of carriers. The imaginary part of the electric modulus shows a peak at low frequencies related to conduction processes. The modelisation of this peak allows us to obtain the dependence of the conductivity (σ₀), the fractional exponent (n) and the crossover frequency (ω_p) on the temperature, among other parameters. The α relaxation, which appears at higher frequencies, has also to be modeled 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 associated with thermal agitation.