Thermal expansivities of aqueous solutions of 2-butoxyethanol in the water-rich region: transition of mixing scheme

Abstract

Thermal expansivities of aqueous solutions of 2-butoxyethanol (BE) were measured at concentrations of xBE < 0.04, where xBE is the mole fraction of BE. Thermal expansivity is a second derivative of the Gibbs free energy. The composition derivatives of thermal expansivities, the third derivatives, show peak anomalies at the same loci as the other third derivatives of the Gibbs free energy reported earlier from this laboratory (Can. J. Chem. 67, 671 (1989); J. Phys. Chem. 94, 3879 (1990); J. Phys. Chem. 95, 4119 (1991)). The loci of such anomalies form a boundary that separates two regions of totally different mixing schemes. The mixing scheme in the water-rich region seems to be consistent with the "iceberg formation," the "structure enhancement of H2O by hydrophobic solute," and the "hydrophobic attraction." In the intermediate composition region, the hydrogen bond network of H2O collapses due to the presence of too many molecules of BE, and H2O and BE molecules interact with each other as normal liquid molecules.