Direct correlations between mechanical-relaxation measurements. Differential-scanning-calorimetry data, and thermally stimulated charge-decay results from Teflon-FEP electrets

Commercial Teflon-FEP films from DuPont were studied by means of several different techniques: The complex shear modulus was measured with a torsion pendulum at 1 Hz between -180 and +260°C; the complex dielectric permittivity was studied between 100 Hz and 1 MHz from -150 to +300°C; differential scanning calorimetry (DSC) was used to determine the phase transitions in the temperature range from -150 to +300°C. The results are compared to reported thermally stimulated discharge (TSD) curves for the same polymer. It is found that the known TSD peaks around -80°C, around +80°C, and above +200°C are closely matched by corresponding features of the mechanical, dielectric, and calorimetric measurements which are ascribed to relaxations at the β or glass II transition, at the α or glass I transition, and in the premelting region, respectively. While the origin of these TSD peaks from movements of the polymer molecules is quite certain, the TSD peak around +155°C found on negatively surface-charged samples requires apparently a more complex explanation. Since the TSD peaks of positively and negatively charged electrets from the other Teflons (PTFE, PFA, and AT) are often found at the same temperatures, their respective discharge-current peaks may have the same physical origins