Time-domain dielectric relaxation in polyamide 6, poly(vinyl chloride), ethylene-vinyl acetate copolymer and poly(vinylidene fluoride) |
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Authors: | M. Safari Ardi D. H. McQueen |
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Affiliation: | (1) Department of Polymeric and Textile Materials, Chalmers University of Technology, 412 96 Gothenburg, Sweden;(2) Chalmers Innovation Centre, Chalmers University of Technology, 412 96 Gothenburg, Sweden |
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Abstract: | 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 ratioFd/C was determined, whereFd = (dC/dlnt)max is the maximum (inflexion) slope of the capacitance versus log(time) dipole response curve, and C is the difference between the initial and the extrapolated equilibrium capacitance values. A modified KohIrausch-WiIIiams-Watts (stretched exponential) function provided a good fit to the measuredC(t) data. For low temperatures, typically below – 20°C,Fd/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. |
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