Dielectric Materials for Electrical Engineering

Chapter 4

Dielectric Relaxation in Polymeric Materials 1

4.1. Introduction

Over this last decade, the technological development of dielectric spectroscopy on the one hand [MCC 67], [BLY 79], [KRE 02], and dielectric thermal analysis on the other [VAN 75], [HED 77], [RUN 97], have allowed the development of dielectric relaxation studies in a wide frequency (from 10−6 to 10+11 Hz) and temperature range, thus leading to a new approach of behavior laws of dielectric relaxation in polymeric materials. In the same way, the development of physico-chemistry and polymer physics [CAR 99], [FON 02], [RAU 02], [HAL 06], [PER 92], [STR 97] has improved the interpretation of the mechanisms observed at a molecular scale.

4.2. Dynamics of polarization mechanisms

The polarization mechanisms are of different origins: (1) from the modification of spatial distributions of electronic and ionic elementary particles and (2) from the reorientation of dipolar entities. These mechanisms are multi-scale and the kinetics to establish the polarization exists at very different time and frequency ranges. We are going to cite them in order of increasing establishment time.

4.2.1. Electronic and ionic polarization

Under the influence of an external electric field, the electronic orbits are distorted with very fast kinetics (10−15 s) causing electronic polarization (see Figure 4.1). The ionic displacements will be made with slower kinetics (10−13 s): they are responsible for the ionic polarization (see Figure 4.1 ...