Thermally stimulated discharge of electrets

Dielectric studies of chain dynamics in homogeneous semi-interpenetrating polymer networks

“…The latter corresponds to a dielectric relaxation time of ϭ 100 s, in agreement with experimental results showing that in many systems, (T m ) is in the range of 100 s. 31,33 The equivalent frequency of TSDC measurements is defined as the frequency of DRS measurements, which would give a loss peak at T m . 31 For the ␣ relaxation associated with the glass transition of the PUR SS microphase, an additional point has been included in Figure 3, with its coordinates being given by T g determined by DSC and the equivalent frequency of 1.6 mHz. The equivalent frequency of DSC measurements can be calculated from the cooling rate of the measurements and the mean temperature fluctuation 41 and has very often been found in the region of millihertz.…”

“…In fact, other conventions have also been proposed; for example, Sauer et al 45 suggested using f eq ϭ 10 Hz for the transformation of DRS data to T g values, corresponding to ϭ 0.016 s, whereas Cendoya et al 10 used ϭ 1 s. The comparison between T g and T ␣ is more straightforward, as both quantities are directly measured. In general, T ␣ and T g have been found to agree rather well with each other for several polymeric systems, 31,33 although, in prin- Figure 5. Arrhenius plot of the samples indicated on the plot.…”

“…It corresponds to measuring dielectric losses against temperature at constant low frequencies of 10 Ϫ2 -10 Ϫ4 Hz. 31,33 In this method, a sample is inserted between the plates of a capacitor and polarized by the application of electric field E p at temperature T p for time t p , which is large in comparison with the relaxation time at T p of the dielectric dispersion under investigation. With the electric field still applied, the sample is cooled to temperature T o (which is sufficiently low to prevent depolarization by thermal excitation) and then is short-circuited and reheated at a constant rate b.…”

“…In addition, the high sensitivity of TSDC allows the detection of weak relaxation mechanisms. 31,33 A homemade experimental apparatus for TSDC measurements was used in the temperature range 77-320 K. 33 The samples, cut from the films, were cylinders 13 mm in diameter. The electrodes (capacitor plates) were made of brass.…”

“…TSDC measurements on several glass-forming systems have shown that the peak temperature T ␣ of the TSDC ␣ peak (temperature of the current maximum) is close to the calorimetric T g and can be considered a measure for that. 31,33,34 Table I lists the values of T ␣ obtained by TSDC and of T g obtained by DSC for PUR and for the IPNs with 80 and 70% PUR. They are in rather good agreement with each other and show the same trend.…”