Thermodynamics of heterogeneous binary condensation on insoluble nuclei

We consider heterogeneous binary condensation as the formation of wetting f ilms of arbitrary thickness on insoluble nuclei. Using this approach, we sh ow that the concurrence of the capillary and disjoining pressures in thin f ilms plays a key role in the thermodynamics of the whole process. The limit ing partial supersaturations necessary for barrierless condensation are obt ained as functions of the droplet composition and an explicit expression fo r the formation free energy of a binary droplet on an insoluble nucleus is derived. The surface describing the formation free energy as a function of film thickness and composition has a minimum and a saddle point whose coord inates correspond to droplets in stable and unstable equilibria, respective ly, with the vapor mixture. Equations for determining the coordinates of th e well and saddle points are presented. The theoretical results are illustr ated with numerical calculations for the butanol-hexanol and butanol-water droplets formation on quartz particles.