Ultrasound Speeds and Molar Isentropic Compressions of Aqueous 2-(Ethylamino) ethanol Mixtures from 283.15 to 303.15 K

Ultrasound speeds in 31 aqueous binary mixtures of 2-(ethylamino)ethanol (EEA) were experimentally determined over the entire composition range at 283.15, 288.15 and 303.15 K. Isentropic compressibilities, kappa(S), were calculated by combining the ultrasound speed with density data. Excess molar isentropic compressions, K(S,m)(E), referred to a thermodynamically-defined ideal liquid mixture, were estimated. Excess partial molar isentropic compressions, K(S,i)(E), of both components and their respective limits at infinite dilution, K(S,i)(E,infinity), were analytically obtained using Redlich-Kister type equations. The temperature and composition dependences of K(S,i)(E) were analyzed, especially in the water and EEA rich regions. The present K(S,i)(E,infinity) values are compared with those for water +2-diethylaminoethanol (DEEA) and water + diethylamine (DEA) mixtures, as a function of temperature. Although the K(S,2)(E,infinity) values for EEA and DEEA increase with temperature, the opposite trend is observed for DEA. Results for aqueous EEA and aqueous DEEA seem to support the idea that the driving force for hydrophobic hydration relies on solute-solvent hydrophilic interaction rather than on enhancing the water structure. On the other hand, different temperature dependent behavior is observed for the differential volumetric properties K E,8 S, i and limiting excess partial molar isobaric expansion, K(S,i)(E,infinity), which are attributed to the different sensitivity of these properties to hydration.