Ultrasonic speeds and volumetric properties of binary mixtures of water with poly(ethylene glycol)s at 298.15 K

Ultrasonic speed measurements have been made by a sonic solution monitor using a 'pulse-echo-overlap' technique, for aqueous mixtures of the poly(ethylene glycol)s di-, tri- and tetra(ethylene glycol) at 298.15 K, across the entire composition range. Density values were taken from the literature and readily converted to molar volumes, V, and excess molar volumes, V-E. They were combined with the measured values of the ultrasonic speeds to furnish estimates of the isentropic molar quantity, K-S, equal to -(partial derivative V/partial derivative p)(S), and of its excess counterpart, K-S(E). The magnitude of K-S(E) decreases with the number of oxyethylene groups, except in the water-rich region. 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 ethane-1,2-diol-water and for 2-[2-methoxy(ethoxy)(n)]ethanol-water. Graphs of the data sets are presented to furnish a basis for the discussion of evidence for the prevailing patterns of molecular aggregation. Segmented-composition models were employed to analyse the various excess molar quantities.