Thermodynamics of heterogeneous multicomponent condensation on mixed nuclei

We consider a nucleating center consisting of both an insoluble core and so luble species and develop the thermodynamics of isothermal formation of a d roplet on such a nucleus in a multicomponent vapor mixture. Two different a pproaches to the derivation of the free energy of droplet formation within the framework of the capillarity approximation are considered. If condensat ion is not barrierless, the free energy of formation describes a multidimen sional free-energy surface having a "well" point and a "saddle" point. It i s shown that in a strict theory, taking account of surface enrichment effec ts, the compositions of droplets corresponding to these two points are equa l and can be found without knowing the surface tension of the droplet. For the case of no surfactants in the droplet, we extend the Kuni method of inv estigating the behavior of the free energy of droplet formation to the case of heterogeneous multicomponent condensation on mixed nuclei, which makes it possible to find out all the main features of the free-energy surface wi thout explicitly knowing the free-energy itself. The theoretical results ar e illustrated by numerical calculations for the water-methanol condensation on mixed nuclei. (C) 2000 American Institute of Physics. [S0021-9606(00)00 733-9].