Volumetric properties of binary mixtures of water with methoxy(ethoxy)nethanols

Abstract

Density and ultrasonic speed measurements have been made, respectively, by means of a densimeter operating in a flow mode and by a sonic solution monitor using a ‘sing-around’ technique, for aqueous mixtures of 2-(2-methoxyethoxy)ethanol and 2-[2-methoxy(ethoxy)₂]ethanol, at 298.15 K, across the entire composition range. The density values were readily converted to molar volumes, V, and excess molar volumes, V^E. Estimates of the isentropic molar quantity, K_s, equal to –(∂V/∂p)_s, and of its excess counterpart, K^E_S, have been obtained from the density values, in combination with the ultrasonic speed values. The magnitude of V^E increases with the introduction of oxyethylene groups into the molecule of amphiphile. The composition dependence of K^E_S shows a similar increase, but one that is limited to the water-rich region. Data reduction procedures have been used to calculate several related quantities leading to graphs with enhanced visual impact. Our results have been compared with those reported earlier for methanol–water, and 2-methoxyethanol–water. Graphical analyses of the data sets are presented in an effort to find a plausible rationale for the observed trends in terms of prevailing patterns of molecular aggregation, while the various excess quantities considered are analysed using a segmented-composition model.