Isobaric expansions and isentropic compressions of aqueous binary mixtures of 2-diethylaminoethanol from 283 to 303 K

Abstract

Densities and ultrasound speeds were determined in aqueous binary mixtures of 2-diethylaminoethanol over the whole composition range at intervals of 5 K in the temperature range between 283 and 303 K. Thermal expansibility effects on this amphiphile/water mixture are analysed in terms of excess molar isobaric expansions EEP,m for the mixture and of excess apparent molar isobaric expansions EEP,ϕ,i for both chemical substances in the mixture. Different strategies are used and discussed for obtaining limiting (infinite dilution) excess partial molar isobaric expansions. Compressibility effects are described in terms of excess molar isentropic compressions KES,m and excess partial molar isentropic compressions KES,i. The latter properties are analytically calculated from the fit of experimental KES,m data to a Redlich–Kister equation. A method based on this equation yields limiting excess partial molar isentropic compressions. Additionally, excess ultrasound speeds uE are also examined. All these excess properties are referred to a thermodynamically defined ideal liquid mixture. Interesting insights into the mixing process are gained from the visual impact of plots showing the composition and temperature dependence of different excess molar thermodynamic properties. Comparison of expansibility- and compressibility-related quantities shows that these two types of thermodynamic properties probe different aspects of intermolecular and packing effects on the process of mixing amphiphiles and water.