Interfacial Properties of tert-Butyl Alcohol Solutions and Their Relation to Clathrate Formation

According to a previous report (Glinski, J.; et al. J. Chem. Phys. 1996, 102, 8816) the surface entropy of the tert -butyl alcohol/water system shows a maximum with respect to solute concentration. Such a maximum was formerly related to the formation of clathrate structures at the interfacial region. However, more complex behavior has also been observed in other aqueous systems. It is currently believed that the surface entropy maxima may reflect structural changes similar to a phase transition and specific interactions between solute molecules. To test the clathrate hypothesis, the thermodynamic properties of tert -butyl alcohol at water, heptane, and water/heptane interfaces were evaluated. For this purpose, the variation of the surface/interfacial tension as a function of temperature and solute concentration was measured, employing Wilhelmy plate and Du Noüy ring techniques. In aqueous tert -butyl alcohol solutions, the maximum of entropy found by Glinski et al. is reproduced. The absence of a large maximum of surface entropy when heptane is used instead of water provides further support to the connection between surface clathrate formation and the anomalous behavior previously observed at tert -butyl alcohol/water interfaces. However, some relevant critical points of lower magnitude are observed in the presence of the organic phase. An alternative explanation on its probable origin more related to effective intermolecular interactions rather than to clathrate formation and phase transitions is discussed.