Volumetric and Viscosimetric Measurements for Methanol + CH$_3$-O-(CH$_2$CH$_2$O)$_n$-CH$_3$ ($n$ = 2, 3, 4) Mixtures at (293.15-303.15) K and Atmospheric Pressure: Application of the ERAS Model

TL;DR

This study measures densities and viscosities of methanol with linear polyethers at various temperatures, analyzing excess properties and applying the ERAS model to understand structural effects in these mixtures.

Contribution

It provides new experimental data on densities and viscosities for methanol-polyether mixtures and evaluates multiple viscosity correlation models, highlighting the effectiveness of the Hind equation and the influence of structural effects.

Findings

Excess molar volumes are large and negative, indicating dominant structural effects.

Viscosity deviations are positive and correlate with volume differences.

The ERAS model partially describes the composition dependence of excess molar volumes.

Abstract

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 CH$_3$-O-(CH$_2$CH$_2$O)$_n$-CH$_3$ ($n$ = 2,3,4). The $\rho$ values are used to compute excess molar volumes, $V_{\text{m}}^{\text{E}}$, and, together with $\nu$ results, 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: Grunberg-Nissan, Hind, Frenkel, Katti-Chaudhri, McAllister and Heric. Calculations show that better results are obtained from the Hind equation. The $V_{\text{m}}^{\text{E}}$ values are large and negative and contrast with the positive excess molar enthalpies, $H_{\text{m}}^{\text{E}}$, 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 volume 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 + CH$_3$-O-(CH$_2$CH$_2$O)$_n$-CH$_3$ mixtures have been treated in the framework of the ERAS model. Results on $H_{\text{m}}^{\text{E}}$ are acceptable, while the composition dependence of the $V_{\text{m}}^{\text{E}}$ curves is poorly represented. This has been ascribed to the existence of strong dipolar and structural effects in the present solutions.