Dielectric Relaxation of Solid Polymers

Abstract

The essential features of the dielectric relaxation behaviour selected amorphous and crystalline polymers are considered. For amorphous polymers it is shown that three dipole relaxation processes are generally observed whose magnitudes and frequency locations depend upon temperature and applied pressure. The phenomenological aspects of the observed behaviour are considered and the similarities to the multiple dielectric relaxations for small-molecule glass-forming systems are emphasized. The molecular theory for dipole relaxation in amorphous polymers is briefly considered. It is shown that the β-process is due to the partial relaxation of dipoles in a range of temporary local environments whilst the a and (α β) processes are due to gross micro-brownian motions of chains, or, for small-molecule glass-forming systems, are due to overall motion of whole molecules, activated by local thermal fluctuations in the system. The dielectric behaviour of certain partially-crystalline polymers, especially polyethylene terephthalate, poly(ethylene), poly(vinylidene fluoride) and oxide polymers, is briefly discussed.