Thermostimulated depolarization currents in thermorheologically simple materials

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Abstract
A theory is presented which makes possible the calculation of the dielectric parameters for a distributed dipole relaxation from thermostimulated depolarization current (TDC) data. The theory is applicable to dielectrics which obey the time–temperature superposition principle, i.e., for thermorheologically simple materials. The shift factor, the activation energy, the dielectric relaxation strength, the density of the isothermal displacement current, and the distribution function of relaxation times of the β relaxation in poly(methyl methacrylate) are calculated. The TDC investigations were carried out over the temperature range of −136 to 90°C. The values for the activation energy U = 26.4 kcal/mole and the dielectric relaxation strength Δϵβ = 2 are in good agreement with values obtained from dynamic measurements. A criterion for checking the validity of the time–temperature superposition principle by TDC is suggested.

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