Heterogeneous nucleation of n-butanol vapor on submicrometer particles of SiO2 and TiO2

Condensation of a supersaturated vapor of n-butanol on monodisperse submicrometer particles is investigated in a how cloud chamber (FCC). The size dependence of critical supersaturation in the range of 20 to 90 nm is experimentally determined. Two types of aerosol SiO2 and TiO2, are tested. The results show that both aerosols induce heterogeneous nucleation better than perfectly wetted particles. The experimental critical supersaturation is smaller than that predicted by the Fletcher version of Volmer theory of heterogeneous nucleation even with the line tension and surface diffusion taken into account and has a size dependence in qualitative agreement with that theoretically predicted but to a lesser degree. The discrepancy can not be fully accounted for by the effects of line tension and surface diffusion and the existing theory concerning the curvature-dependent physical properties. The law of corresponding states was extended to the heterogeneous nucleation, and a simple correlation was observed. We conclude that the macroscopic theory of heterogeneous nucleation leads to a prediction of critical supersaturation higher than that experimentally measured. (C) 1999 Academic Press.