Intermolecular Interactions in tert-Butyl Alcohol−Dimethyl Sulfoxide−H2O: Chemical Potentials, Partial Molar Entropies and Volumes

Abstract

The excess chemical potentials, the excess partial molar entropies, and the partial molar volumes in tert-butyl alcohol (TBA)−dimethyl sulfoxide (DMSO)−H2O mixtures were determined. These data, together with previously published excess partial molar enthalpies (Fluid Phase Equilib. 1997, 136, 207) were used to evaluate intermolecular interactions. The TBA−TBA and TBA−DMSO, and DMSO−DMSO interactions were found to be crucially dependent on the composition. The net interaction in terms of chemical potential is very intricate. For example, net interactions of DMSO with a hydrophobic moiety (represented here by TBA) change from attractive to repulsive as the composition changes. This suggests that general discussions of the affinity of DMSO for nonpolar groups (or surfaces) are meaningful only by specifying the composition region. The interactions in terms of enthalpy and entropy are an order of magnitude larger and strongly compensating. Anomalous changes in the enthalpic/entropic interactions and hence qual...