Binary Nucleation of a Nonideal System from Classical and Density Functional Theories

Several versions of classical binary nucleation theory (CBNT) are compared with density functional theory (DFT) results for a nonideal model system that mimics the properties of water-ethanol mixtures. The model is a mixture of hard spheres with attractive Yukawa forces. It predicts a qualitatively correct bulk liquid-vapor phase diagram at 260K. The results are compared as a plot of the vapor activities needed to produce a constant value of the reversible work of cluster formation, W/kT = 40. The classical theories are distinguished by the absence (versions 1 and 2) or presence (version 3) of a compositional surface tension derivative in the Kelvin equations. For low values of the “water” activity, a1, all CBNT versions agree well with DFT. At higher values of the “water” activity, no version of CBNT agrees well with DFT, although for a 1 > 3 the predicted a2 values of versions 1 and 2 are many orders of magnitude closer to the DFT results than are the version 3 values.