Thermally stimulated polarization currents in poly (p-hydroxybenzoic acid-CO-ethylene terephthalate), liquid crystal polymer

Thermally stimulated polarization currents (TSPC) in various samples of poly{p-hydroxybenzoic acid-co-ethylene terephthalate (PET/x PHB)} with different values of x (molar concentration) have been investigated in the temperature range (30 - 250 degrees C) under polarizing fields in the range 6.6 - 133 kV/cm. The low temperature region of TSPC spectra exhibits a peak (a-relaxation) between 40 and 65 degrees C depending on x. This peak has been attributed to polar nature of both PET and PHB, confirmed by the activation energy values (0.14-0.3eV) estimated using initial rise method. A phenomenal rise of several orders of magnitude in the current after a-relaxation seems to be dominated by conducted currents followed by a peak P-2(termed delta-relaxation) in the temperature range 160 degrees-210 degrees C. This peak may be ascribed to die melting crystals, i.e. movement of large segments characterizing a smectic-E like phase. The activation energy values (0.14-0.03 eV) computed from the spectra are consistent with the ones estimated from side group orientation method. The calculated values of dielectric constant at different temperatures are in good agreement with the results obtained by other methods.