Surface thermodynamics of aqueous solutions of alkylethanolamines

The surface tension of aqueous solutions of methyldiethanolamine and dimethylethanolamine has been measured at temperatures from 298.15 to 328.15 K over the whole range of concentrations. The surface tensions of these aqueous binary mixtures show more concentration dependence on the water-rich side. Addition of a small amount of alkylethanolamine reduces the surface tension of water drastically. This effect is related to the presence of hydrophobic groups such as (-CH3) which tend to remain more on the water surface. The thermodynamics of the water surface, the surface entropy and surface enthalpy have been calculated for six (alkylethanolamine + water) mixtures. The surface thermodynamic properties of these mixtures are classified in two categories: those aqueous solutions of ethanolamines with an end hydrophobic group and those without. The surface entropy of the category without an end hydrophobic group is similar to the water surface while the surface properties of the category with an end hydrophobic group are much different from the water surface. (C) 2001 Elsevier Science B.V. All rights reserved.