Conduction mechanisms and high-field effects in synthetic insulating polymers

The absorption and conduction currents in synthetic insulating polymers, viz., polyethylene, polypropylene, polyethylene-terephthalate and polyvinylidenefluoride, with dc fields may be electronic or ionic both and it may be difficult to determine their origins unambiguously. The charges which are present in the bulk of the polymer may be responsible for both the absorption and the conduction current. A limited displacement of charges together with the rotation of side chains may provide a decaying transient current in the presence of an externally impressed field whereas the conduction current may originate from a hopping of charge carriers in which the charges transfer between localized states. The complex dielectric response of these polymers with ac field may also be explained by intra- and inter cluster charge movement which would be consistent with the unified model, stated above for the case of dc fields.