Volumetric and Viscosimetric Measurements for Methanol + CH3–O–(CH2CH2O)n–CH3 (n = 2, 3, 4) Mixtures at (293.15–303.15) K and Atmospheric Pressure: Application of the ERAS Model

Abstract

Densities, ρ, and kinematic viscosities, ν, have been determined at atmospheric pressure and at (293.15-303.15) K for binary mixtures formed by methanol and one linear polyether of the type CH3-O-(CH2CH2O)n-CH3 (n =2,3,4). Measurements on ρand ν were carried out, respectively, using an Anton Paar DMA 602 vibrating-tube densimeter and an Ubbelohde viscosimeter. The ρ values are used to compute excess molar volumes, V_m^E , and, together with ν results, dynamic viscosities (η). Deviations from linear dependence on mole fraction for viscosity, Δη, are also provided. Different semi-empirical equations have been employed to correlate viscosity data. Particularly, the equations used are: Grunberg-Nissan, Hind, Frenkel, Katti-Chaudhri, McAllister and Heric. Calculations show that better results are obtained from the Hind equation. The V_m^E values are large and negative and contrast with the positive excess molar enthalpies,H_m^E, available in the literature, for these systems. This indicates that structural effects are dominant. The Δηresults are positive and correlate well with the difference in volume of the mixture compounds confirming the importance of structural effects. The temperature dependences of ηand of the molar volume have been used to calculate enthalpies, entropies and Gibbs energies,ΔG^*, of viscous flow. It is demonstrated that ΔG^* is essentially determined by enthalpic effects. Methanol + CH3-O-(CH2CH2O)n-CH3 mixtures have been treated in the framework of the ERAS model. Results onH_m^E are acceptable, while the composition dependence of the V_m^Ecurves is poorly represented. This has been ascribed to the existence of strong dipolar and structural effects in the present solutions.