Phase Equilibria in Binary Mixtures of Water with Triglyme and Tetraglyme: Experimental Determination and Thermodynamic Modeling

Abstract

Because of their many favorable properties and specifically balanced amphiphilic nature, glymes (oligomeric ethylene glycol diethers) are of great technological and theoretical interest. This study focuses on the phase equilibria and energetics of aqueous solutions of two important members of the glyme series, triglyme (triethylene glycol dimethyl ether) and tetraglyme (tetraethylene glycol dimethyl ether). For these systems, we carried out accurate measurements of water activity at two temperatures (298.15 and 313.15 or 318.15 K) in the whole composition range, boiling temperatures at three pressures (50, 70, and 90 kPa), and freezing temperatures in the water-rich region. The melting temperature and melting enthalpy of the neat glymes were also determined. We correlated our water activity data simultaneously with some related thermal data from the literature using an extended SSF-type excess Gibbs energy (G E ) model. The established model descriptions provided not only particularly good fit of the underlying data but, as proven by due comparisons to other results from both the literature and this work, showed a superior performance, extrapolating very well to both higher and lower temperatures. The high-fidelity global modeling also enabled us to present a clear picture of the energetics of the two aqueous glymes. At near-ambient temperatures, both systems exhibit nonmonotonous activity coefficient courses with composition, large exothermic effects, and remarkably deep drops of the entropy accompanying the mixing, their positive G E being entropy-driven. On increasing the temperature, the former features gradually decline while G E keeps about the same magnitude and becomes enthalpy-driven. Although both systems show a great tendency to phase splitting above the normal boiling temperature of water, our model calculations predicted the lower critical solution temperature behavior only for the aqueous solution of triglyme. The observed pattern of the energetic behavior has been well elucidated in terms of competitive water−water and water−ether H-bonding.

Polyhedral Oligomeric Silsesquioxane-Based Macroanions to Level Up the Li+ Transport Number of Electrolytes for Lithium Batteries

“…The crystallinity degree (χ) of TEG in these electrolytes can be calculated as follows using the measured melting enthalpy divided by the mass of TEG in the sample (Δ H m (J per gram of TEG)). where Δ H o is the melting enthalpy of a pure TEG taken at 133 J g –1 from the literature …”

“…where ΔH o is the melting enthalpy of a pure TEG taken at 133 J g −1 from the literature. 44 Thermogravimetric Analysis (TGA). Thermogravimetric analysis (TGA) was conducted on a 1 STARe System analyzer from Mettler-Toledo using alumina crucibles by varying the temperature from 25 to 600 °C at a heating rate of 10 °C min −1 with an isotherm of 1 h at 100 °C.…”