Interfacial tensions of ethanol-carbon dioxide and ethanol-nitrogen. Dependence of the interfacial tension on the fluid density - prerequisites and physical reasoning

Interfacial tensions in the systems ethanol-carbon dioxide and ethanol nitrogen are measured. In both systems the interfacial tension decreases with increasing pressure. The interfacial tension in the system ethanol-nitrogen decreases with increasing temperature. In contrast to this, in the system ethanol-carbon dioxide at high pressures an isobaric increase in temperature provokes an increase in interfacial tension. In the system ethanol-carbon dioxide at elevated pressure the density of the carbon dioxide phase is the only influence parameter concerning the interfacial tension. This phenomena can be observed for various other systems with one near critical or supercritical component and a high solubility of this component in the liquid phase and at temperatures above the critical temperature of the gas. For this fact a physical reasoning, which is based on a new concept of partial interfacial tensions, is given. Furthermore, it is stated that the interfacial tension of fatty systems in contact with carbon dioxide has approximately the same dependence on the reduced density (p(r) = p/p(c)) of the supercritical phase as the interfacial tension of the same systems in contact with ethane. The knowledge of this fact can help to avoid experiments with ethane, which is flammable. (C) 2003 Elsevier Science Ltd. All rights reserved.