(10d) Modeling the Surface Tension of Pure Fluids Using the Gradient Theory and a Simple Ceos

The well-known gradient theory of fluid interfaces (GTFI) was combined with a simple cubic equation of state (CEoS) to accurately compute the surface tension of non-polar and polar fluids within a wide range of temperatures: from the triple point up to the critical region. For the majority of the pure fluids under study, a remarkably good representation of experimental surface tensions was obtained near their critical points even though the homogeneous-fluid portion of the GTFI was modeled using a simple CEoS that usually fails to properly describe the fluid phase behavior near the critical point. In an attempt to compensate for this weakness exhibited by the CEoS within the GTFI framework, a new scaling functionality was introduced in this work for the influence parameter of the inhomogeneous fluid. The proposed expression for the influence parameter, which carries the information on the molecular structure of the interface, proved to be highly satisfactory along with the Soave or Peng-Robinson CEoS during the representation of experimental surface tensions of various pure fluids including some normal paraffins, isoparaffins, alcohols, aromatics, ethers, CO2, water, acetic acid, among others.