Study of dielectric relaxation and thermodynamic behaviour in poly(propylene glycol) using Time Domain Reflectometry

Abstract

Temperature dependent dielectric relaxation and thermodynamic energy parameters of polypropylene glycols HO[CH(CH 3)CH 2O) nH with number average molecular weight 425(n = 7), 1000 (n = 17) and 2000 (n = 34) g mol − 1 have been studied using Time Domain Reflectometry (TDR). The frequency dependence of the complex dielectric permittivity is analyzed by the Havriliak-Negami expression. The static dielectric constant ε 0, high frequency limiting dielectric constant ε ∞ , relaxation time τ 0 and thermodynamic energy parameters such as free energy, enthalpy of activation and entropy of activation have been determined. The average free energy of activation ΔF τ for all the three PPG molecules was found to be in the range of 4–5 kcal mol 26 − 1 . The values of entropy ΔS τ for PPG-2000 molecules were found to be negative while entropy ΔS τ for PPG-425 and PPG-1000 molecules found positive, which confirms that the configuration of PPG-2000 involved in the dipolar orientation has an activated state, which is more ordered than in the normal state compared to PPG-425 and PPG-1000 molecules.