Thermodynamic characterization of binary mixtures of poly(propylene glycol) 425 with toluene and o-, m- and p-xylenes

Highlights: • Densities, viscosities and refractive indices of PPG 425 + toluene/xylenes are determined in temperature range. • Detailed thermodynamic interpretation of molecular interactions is performed. • Weak specific attractive interactions between non-polar PPG425 and aromatic solvents are present. • Viscosity of four systems was predicted with UNIFAC-VISCO and ASOG-VISCO models and correlated with the McAllister equation. -- Abstract: Density ρ, viscosity η and refractive index n_D have been experimentally measured for four binary mixtures of poly(propylene glycol) of average molecular weight 425 + toluene/o-xylene/m-xylene/p-xylene over the temperature range T = (293.15–333.15) K with temperature step 5 K and at atmospheric pressure. From the experimental data excess molar volumes V^E, deviations in refractive index Δn_D, viscosity deviations Δη and excess Gibbs free energy of activation of viscous flow ΔG^*E were calculated and fitted with Redlich-Kister polynomial in order to analyze non-ideal behavior of the studied mixtures. From ΔG^* values excess entropy ΔS^*E and excess enthalpy of activation of viscous flow ΔH^*E were also calculated. It was shown that specific weak, but numerous, attractive interactions and entropic effect, due to difference in size of the pure component molecules, are responsible for volumetric and viscosity behaviour of the studied systems. The viscosities of the studied systems were predicted with the UNIFAC-VISCO and ASOG-VISCO models and correlated with the McAllister equation.