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

摘要

The time-domain dielectric responses of polyamide 6 (PA6), poly(vinyl chloride) (PVC), ethylene-vinyl acetate copolymer (EVA) and poly(vinylidene fluoride) (PVDF) to a voltage step were measured at different temperatures. 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) dipole response curve, and Delta C is the difference between the initial and the extrapolated equilibrium capacitance values. A modified Kohlrausch-Williams-Watts (stretched exponential) function provided a good fit to the measured C(t) data. For low temperatures, typically below - 20 degrees C, F-d/Delta C, is about 0.1, characteristic of highly cooperative 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 temperature. [References: 7]