Aggregative processes in aqueous solutions of mono- to tetra-ethylene glycol dimethyl ether at 298.15 K

Abstract

A sonic solution monitor that employs the “pulse-echo-overlap” technique was used to measure ultrasound speeds in binary liquid mixtures of water with mono- to tetra-ethylene glycol dimethyl ether (also known as mono- to tetra-glyme) across their entire composition ranges. In addition, densities of aqueous mixtures of ethylene glycol dimethyl ether (monoglyme) were determined using a vibrating tube densimeter. The new data were complemented with literature values for the densities of aqueous mixtures of di-, tri- and tetra-glyme. All measurements were made at 298.15 K. Densities were converted to excess molar volumes, V^E_m. Combination of the densities and ultrasound speeds provided estimates of the excess molar isentropic compressions, K^E_S,m. The excess thermodynamic properties were converted to excess partial and apparent molar properties of both components of each mixture. Negative values are generally observed for all of the excess molar properties. Graphs are presented to exhibit the effects of extending the length of the polyether chain. Data analyses have been carried out using different versions of the four-segment model for aqueous mixtures of amphiphile substances, one version of which including a mass action component. At a given composition in the transitional segment, it is found that the investigated excess molar properties become approximately insensitive to the chain length in the glyme molecules. Present and previously reported V^E_m data have been combined for constructing series showing the effect of replacing successively the hydroxyl hydrogens in ethan-1,2-diol by methyl groups, as well as increasing the number of ethylene oxide units in 2-methoxyethanol. Along these series of aqueous mixtures, negative excess molar volumes are found to increase in magnitude. Limiting partial molar volumes and isentropic compressions are reported for the glymes in water and for water in the glymes.