Dielectric relaxation of the electric field in poly(vinyl acetate): A time domain study in the range 10^-3-10⁶ s

We have measured the polarization of poly(vinyl acetate) in terms of a real dielectric relaxation technique by studying the decay of the electric field E(t) for times 10^-3 s ≤ t ≤ 10⁶ s under the condition of a constant dielectric displacement for t > 0. This represents a direct measurements of the dielectric modulus M(t), opposed to the conventional method of measuring the dielectric retardation ε(f), or its frequency domain analogue ε*(ω). The advantages of accessing M(t) are a simple experimental set-up and for polar materials experimental times which are shorter by at least a factor of ε_s/ε_∞ relative to ε(t) decays. The latter effect is based on the well-known relation τ_L = ε_∞/ε_sτ_D between transversal and longitudinal dielectric time constants. For the polymer under study, we find that no significant change of the relaxation time distribution occurs within the experimental time window, i.e. from well above the glass transition at T_g (if defined via τ_g = τ(T_g) = 100 s) to temperatures below T_g where the average retardation times (τ) attain values of up to 10⁷ s.