The dielectric relaxation behavior of Polyetheretherketone (PEEK) has been investigated by using thermally stimulated discharge current (TSDC) technique. The dependence of TSDC characteristics of PEEK on poling temperature (T P ) [50-200°C], poling field (E P ) [200-500 kV/cm], storage time (t S ) [2-120 hrs] and various thicknesses 25 μm, 50 μm and 75 μm have been investigated in the temperature range [60-230°C]. The TSDC spectra shows a prominent maxima around glass transition temperature (T g ) i.e. at 143°C named as α-peak and the other peak is observed around 200°C named as β-peak. The α-dipolar relaxation is taking place because of the movement of ketone (>C 00) dipoles linked to the main chain. The β-peak is attributed to the space charges. It is observed that the magnitude of α-peak increases with the increase in poling field. The peak current and area under the α-peaks are found to be diminished with the increase of storage time (t s ) for electrets. The amplitude of α-peak decreases with the increase in thickness. The activation energies for PEEK sample at different conditions in the present work are found to be 0.38 eV-1.70 eV. The values of activation energy (U) and preexponential factor (C o ) for α-relaxation are determined using Bucci plot method and support the nature of the relaxations.
The dielectric constant (ε') and dielectric loss (ε)״ of pristine and C 5+ (70 MeV) ion irradiated samples of the PEEK have been investigated with the variation of temperature at different frequencies (100 Hz, 1 kHz, 10 kHz and 100 kHz). The maxima are obtained around 170 o C in dielectric constant (ε') vs. temperature (T) curve. This relaxation is linked with the movement of ketone (>C=0) dipoles linked to the main chain. The irradiation of polymers increases the orientational polarization due to increase in number of dipoles with fluence. The increase in dielectric constant (ε') and dielectric loss (ε'') is attributed to chain scissioning at higher fluence which results in an increase of free radicals and unsaturations.
The most significant advantage of studying the charge storage mechanism of Vectra-A, Liquid Crystal Copolyester through Dielectric Spectroscopy (DS) is their complex structure, which can be physically or chemically tailored for specific applications which make it suitable for charge storing devices like Micro-Electro-Mechanical Systems (MEMS). The variation of dielectric constant (ε') and dielectric loss (ε'') in the temperature interval (25 o C to 250 o C) for pristine samples of Vectra-A at different frequencies (1 kHz to 1 MHz) have been investigated.
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