The adsorption and nucleation of water vapor on an insoluble spherical solid particle

A kinetic theory with consideration of surface migration is derived for heterogeneous nucleation of water on a smooth spherical solid particle. In this model, the adoption of the kinetic coefficient for the calculation of nucleation rate, whose value is somewhat uncertain, is avoided. The effects of particle size and contact angle between the condensate and particle surface on the critical supersaturation ratio were investigated. The calculated critical supersaturation is lower compared with that of the classical theory proposed by Fletcher, and higher than that obtained by Scheludko's theory, which took into account the effect of a negative line tension. A comparison with experimental data shows that the contact angle between water and Ag particles is about 40 degrees and that for dioctyl phthalate (DOP) aerosol is about 5 degrees. The results indicate that the assumption of a hydrophilic adsorbed layer on the DOP surface is nor necessary. We also find that for the onset of heterogeneous nucleation processes, the indirect addition of the adsorbed molecules to the condensate nuclei by two-dimensional diffusion is more important than the direct addition of the molecules from the vapor phase. In general, the predicted critical supersaturation is higher than the experimental values and the discrepancy cannot be accounted for simply by the consideration of indirect addition of adsorbed molecules in this model. (C) 1998 Elsevier Science B.V. All rights reserved.