Positron annihilation response and broadband dielectric spectroscopy: Poly(propylene glycol)

Abstract

The results of phenomenological analysis of the ortho-positronium (o-Ps) lifetime, τ 3 , from positron annihilation lifetime spectroscopy (PALS) and of the dielectric relaxation spectra from broadband dielectric spectroscopy (BDS) on poly(propylene glycol) (PPG) are presented. A number of coincidences between the characteristic PALS temperatures T g PALS , T b 1 L and T b 2 L obtained from a phenomenological analysis of a quasi-sigmoidal PALS response and the various characteristic BDS temperatures for the spectral and relaxation parameters have been revealed. Thus, an onset of the quasi-plateau level at the PALS temperature T b 2 L = 1.44 T g PALS is characterized by the equality of the o-Ps lifetime, and the primary relaxation time: τ 3 ≅ τ α . Moreover, a deviation toward the quasi-plateau level at T b 2 L is related to a saturation in both spectral width and relaxation strength parameters of the α-process and a merging of the relaxation times of the primary ( α) and secondary ( β)-processes. In addition, T b 2 L lies in the vicinity of a high-temperature crossover of the main relaxation process from the non-Arrhenius to the Arrhenius behavior. The another characteristic PALS temperature, T b 1 L = 1.18 T g PALS , is also connected with the change in temperature behavior of time and strength parameters of the secondary effective β-relaxation. All these findings indicate a close connection between the PALS response and the dielectric relaxation in PPG.