TRANSITION OF MIXING SCHEME IN THE WATER-RICH REGION OF AQUEOUS 2-BUTOXYETHANOL - PARTIAL MOLAR VOLUMES AND THEIR DERIVATIVES

The mixing scheme boundary proposed in paper 1 (J. Phys. Chem. 1990, 94, 3879) was extended to high temperatures. Using the data of the excess partial molar volumes in aqueous solutions of 2-butoxyethanol (BE), V(m)E(i) (i = BE or H2O), reported in paper 2 (J. Chem. Thermodyn., in press), the composition derivatives of V(m)E(BE), (partial derivative V(m)(BE)/partial derivative n(BE))n(W), were calculated. n(BE) and n(W) are the amounts of BE and H2O in solution, respectively. It was found that these derivatives showed peak anomalies at the same loci of the mixing scheme boundary. In the water-rich region below the boundary, the behavior of the partial molar volumes and their derivatives was explained in a consistent manner as presented in previous papers (Can. J. Chem. 1989, 67, 67 1; J. Phys. Chem. 1990, 94, 3879; J. Phys. Chem. 1991, 95, 4119). We took into account three effects on V(m)E(BE): (1) the size difference between BE and W molecules; (2) the packing density of solvent H2O; (3) the progressive enhancement of the hydrogen-bond network of H2O as the concentration of BE increases.