DENSITY PROFILES AT LIQUID-VAPOR AND LIQUID-LIQUID INTERFACES - AN INTEGRAL-EQUATION STUDY

The structure of liquid-vapor and liquid-liquid interfaces in Lennard- Jones (LJ) fluids and mixtures is studied using integral equations. To obtain density distributions at interfaces between coexisting fluid p hases we solve the Lovett-Mon-Buff-Wertheim equation. In this equation we approximate the direct correlation functions of the inhomogeneous fluid via interpolation between the direct correlation functions of th e bulk phases. In the homogeneous bulk phases the system of the Ornste in-Zernike equation with the reference-hypernetted-chain closure is so lved to obtain the direct correlation functions at coexisting densitie s. Density distributions and other interfacial properties are studied for a liquid-vapor interface in a pure LJ fluid, in an Ar-Kr mixture a nd for a liquid-liquid interface between two immiscible LJ fluids. The results are in good agreement with simulations and other theories. At low temperatures the liquid-vapor and liquid-liquid density profiles exhibit oscillating structures with periods near the diameters of the LJ spheres. Being quite weak at liquid-vapor interfaces these oscillat ions become very pronounced at a liquid-liquid interface between immis cible fluids. (C) 1997 American Institute of Physics. [S0021-9606(97)5 2341-5].