Ultrasonic speeds and volumetric properties of binary mixtures of water with 2-[2-(2-alkoxyethoxy)ethoxy]ethanols at 298.15 K
Density and ultrasonic speed measurements have been made using vibrating tube densimeters and by a sonic solution monitor using a ‘pulse-echo-overlap’ technique, respectively, for aqueous mixtures of 2-[2-(2-ethoxyethoxy)ethoxy]ethanol and 2-[2-(2-butoxyethoxy)ethoxy]ethanol, at 298.15 K, across the entire composition range. The density values were readily converted to molar volumes, V, and excess molar volumes, VE. Estimates of the isentropic molar quantity, Ks, equal to –(∂V/∂p)s, and of its excess counterpart, KEs, were obtained from the density values, in combination with the ultrasonic speed values. The magnitude of VE decreases with the alkyl-chain length, except in the water-rich region. The composition dependence of KEs shows a similar decrease. Data reduction procedures were used to calculate several related quantities leading to graphs with enhanced visual impact. Results were compared with those reported earlier for 2-[2-(2-methoxyethoxy)ethoxy]ethanol–water and 2-[2-(2-hexyloxyethoxy)ethoxy]ethanol–water, and for 2-butoxyethanol–water and 2-(2-butoxyethoxy)ethanol–water. Graphs of the data sets are presented as a basis for discussion of evidence for prevailing patterns of molecular aggregation. Segmented-composition models, including a version onto which a mass-action component has been grafted, were used to analyse the various excess molar quantities.