Application of density functional theory for predicting the surface tension of pure polar and associating fluids

A thermodynamic method has been developed based on the density functional theory (DFT) to predict the surface tension of polar and associating fluids by the authors. The Barker-Henderson (BH) perturbation theory and statistical associating fluid theory (SAFT) are used to establish the equation of state (EOS). The hard sphere repulsion, dispersion, chain formation. and dipole-dipole or association interactions are taken into account. The parameters m, sigma and epsilon/k for non-associating polar fluids and m, sigma, epsilon/k, epsilon(AB) /k and kappa(AB) for associating fluids are correlated by simultaneously fitting the saturated vapor pressure and the liquid density data with the EOS. The surface region of a pure liquid is divided into many extreme thin layers. The chemical potential in every layer of the surface leads to a constant by optimizing the surface thickness. The density profile is obtained from the optimized surface thickness and the hyperbolic tangent function obtained from molecular simulation. By use of the obtained density profile and the regressed parameters in EOS, the surface tensions for four pure non-associating polar fluids and 11 associating fluids in wide temperature range are predicted satisfactorily. (C) 2002 Elsevier Science B.V. All rights reserved.