TIME-DOMAIN DIELECTRIC-RELAXATION IN POLYAMIDE-6, POLY(VINYL-CHLORIDE), ETHYLENE-VINYL ACETATE COPOLYMER AND POLY(VINYLIDENE FLUORIDE)

The time-domain dielectric responses of polyamide 6 (PA6), poly(vinyl chloride) (PVC), ethylene-vinyl acetate copolymer (EVA) and poly(vinyl idene fluoride) (PVDF) to a voltage step were measured at different te mperatures. From the variation of the sample capacitance, C, with time , the ratio F-d/Delta C was determined, where F-d = (dC/dInt)(max) is the maximum (inflexion) slope of the capacitance versus log(time) dipo le response curve, and Delta C is the difference between the initial a nd the extrapolated equilibrium capacitance values. A modified Kohlrau sch-Williams-Watts (stretched exponential) function provided a good fi t to the measured C(t) data. For low temperatures, typically below - 2 0 degrees C, F-d/Delta C, is about 0.1, characteristic of highly coope rative relaxation, while at higher temperatures the ratio approaches 1 /e, characteristic of nearly independent (Maxwellian) relaxation. This is in contrast to corresponding analyses of mechanical relaxation in solids for which the constant is almost always near 0.1 at room temper ature.