Dielectric relaxation study of poly(ethylene glycols) using TDR technique

Temperature dependent dielectric relaxation and thermodynamic properties of polyethylene glycols HO[CH2-CH2-O) H with number average molecular weight 200 (n = 4), 300 (n = 7), 400 (n = 9) and 600 (n = 14)g mol(-1) have been studied using Time Domain Reflectometry (TDR) in the frequency range 10 MHz to 20 GHz. The frequency dependence of the complex dielectric permittivity is analyzed by the Havriliak-Negami expression. The static permittivity epsilon(0), high frequency limiting static permittivity epsilon(infinity), average relaxation time To and thermodynamic energy parameters such as free energy, enthalpy of activation and entropy of activation have been determined. The average free energy of activation AFT for PEG molecules was found to be in the range 4-5 kcal mol(-1). The values of entropy Delta S-tau for PEG-200, PEG-400 and PEG-600 molecules were found to be positive while entropy Delta S-tau for PEG-300 molecules was found negative, which confirms that the configuration of PEG-300 involved in the dipolar orientation has an activated state, which is more ordered than the normal state compared to PEG-200, PEG-400 and PEG-600 molecules. (C) 2011 Elsevier B.V. All rights reserved.