Binary heterogeneous nucleation of water−n-propanol and water−sulfuric acid mixtures has been investigated. The classical thermodynamically consistent theory has been used. In the case of the water−n-propanol system, physically unrealistic predictions are seen. At water−gas-phase activities above 1, the theory predicts negative molecular occupation numbers of water in the critical clusters. In the case of water−sulfuric acid, however, the predictions are realistic. A series of quantitative experiments of heterogeneous nucleation of water−n-propanol on oxidized silver particles have been performed, and the results are contrasted with the theoretical predictions.

In this Letter, we report the first experimental study of binary heterogeneous gas-liquid nucleation. Onset activities were obtained for nucleation of various n-propanol-water vapor mixtures on 6.9 nm NaCl particles soluble in water and practically insoluble in n-propanol. The Fletcher theory of vapor nucleation on insoluble particles provided a reasonable approximation for n-propanol rich mixtures only, whereas the Köhler theory of activation of soluble particles worked only for water rich mixtures. A new theory was formulated providing a satisfactory description of the transition from activation of soluble particles to vapor nucleation on insoluble particles.

Heterogeneous nucleation of binary n-propanol - water vapor mixtures on non-soluble or partially soluble 8nm Ag and NaCl particles has been investigated experimentally. At constant temperature the vapor activities have been stepwise increased and the number of particles activated to condensational growth shows a comparatively steep increase until all particles have been activated. Onset activities were obtained for various mixing ratios of the binary vapor mixtures. In contrast to homogeneous nucleation, for binary heterogeneous nucleation only a conucleation without significant mutual enhancement was observed. Heterogeneous nucleation calculations based on Fletcher theory using experimentally obtained contact angles have been performed. Satisfactory agreement of the slopes of the nucleation probability curves was observed. However, considerable deviations between experimental and theoretical onset activities indicate problems of the binary nucleation theory based on the capillarity approximation. For NaCl particles and water rich mixtures the Kohler theory is in good agreement with the experimental data. On the other hand, for n-propanol rich mixtures and NaCl particles the heterogeneous nucleation calculations based on Fletcher theory provide a reasonable approximation of the experimental data. It appears that neither Fletcher nor Kohler theory are applicable to NaCl particles in the region of transition from water rich to n-propanol rich mixtures.