Surface Tension Prediction Using Characteristics of the Density Profile Through the Interfacial Region

Abstract

A simple surface tension estimation technique is described that is based solely upon the characteristics of the density profile in the interfacial region and the physical properties of the molecules in the fluid. This method, denoted free energy integration (FEI), links interfacial tension to known interfacial region density profile characteristics obtained via experiment or simulation. The general FEI methodology is provided here, and specific relations are derived for a methodology that incorporates the Redlich–Kwong fluid model. The Redlich–Kwong based FEI method was used to predict interfacial tension using the density profile characteristics of molecular dynamics (MD) simulations of argon using the Lennard–Jones potential, diatomic nitrogen using the two-center Lennard–Jones potential, and water using the extended simple point-charge (SPC/E) model. These results for argon compare favorably to values calculated by the traditional virial approach, known values from the literature using the finite-size scaling technique, and ASHRAE recommended values. In addition, the FEI predictions agree well with ASHRAE values and predictions using the virial method for nitrogen for the simulated range of temperatures in this study, and for water for reduced temperatures above 0.7. In addition, the FEI method results agree well with other established theoretical techniques for predictions of the surface tension of sulfur hexafluoride close to the critical point.