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

摘要

Densities, rho, and kinematic viscosities, nu, 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 rho and nu were carried out, respectively, using an Anton Paar DMA 602 vibrating-tube densimeter and an Ubbelohde viscosimeter. The rho values were used to compute excess molar volumes, VmE, and, together with the nu r esults, dynamic viscosities (eta). Deviations from linear dependence on mole fraction for viscosity, Delta eta, are also provided. Different semi-empirical equations have been employed to correlate viscosity data. Particularly, the equations used are the: Grunberg-Nissan, Hind, Frenkel, Katti-Chaudhri, McAllister and Heric. Calculations show that better results are obtained from the Hind equation. The VmEdocumentclassvalues are large and negative and contrast with the positive excess molar enthalpies, HmE, available in the literature, for these systems. This indicates that structural effects are dominant. The Delta eta results are positive and correlate well with the difference in volumes of the mixture compounds, confirming the importance of structural effects. The temperature dependences of eta and of the molar volume have been used to calculate enthalpies, entropies and Gibbs energies, Delta G*, of viscous flow. It is demonstrated that Delta G* is essentially determined by enthalpic effects. Methanol + CH3-O-(CH2CH2O)(n)-CH3 mixtures have been treated in the framework of the ERAS model. Results for HmEare acceptable, while the composition dependence of the VmEcurves is poorly represented. This has been ascribed to the existence of strong dipolar and structural effects in the present solutions.