Correlation of dielectric and visco-elastic relaxation in polymer solutions

Abstract

The interpretation of studies of dielectric relaxation in polymers is often restricted by ignorance of the mode of motion responsible for dipole orientation in an applied field. Relevant information can be drawn from studies of visco-elastic relaxation, since the visco-elastic relaxation time is comparable with the dielectric relaxation time when the latter requires some ‘whole molecule’ mode of motion involving simultaneous movement of many chain segments. The dielectric and visco-elastic relaxation times are expected to differ when the former involves a localised segmental motion. The dielectric relaxation process is shown to involve a localised segmental motion in acrylic polymers, but involves a ‘whole molecule’ rotation in low molecular weight poly(N-vinylcarbazole). Poly(p-substituted phenyl acetylenes) exhibit two dielectric relaxation processes. A low frequency relaxation comparable with the visco-elastic relaxation is ascribed to the backbone double bonds being polarised unidirectionally along the chain, and a high frequency process is ascribed to a localised segmental motion of the substituted phenyl moiety.