Journal of Physical Chemistry B, Vol.105, No.47, 11817-11822, 2001
Nucleation rate surface topologies for binary systems
Recent experiments have found that two nucleation rate surfaces can be observed for two different critical embryo phases (solid and liquid) near the triple point of the condensing species. Direct experimental evidence was presented of the existence of two independent nucleation rate surfaces with one of them existed over metastable vapor-liquid-phase equilibrium lines. These results force more careful consideration of the role of metastable phase equilibria in the topology of nucleation rate surfaces. In the present study, the topology of the nucleation rate surface for a binary vapor in which partial solubility of the condensed components is considered. Schematic multiple surfaces over the phase diagram with a eutectic point, presenting two-channel nucleation, are constructed. Vapor-liquid nucleation in a carrier gas in most cases is a binary system with partial solubility of condensate. It is reasonable to propose that multiple nucleation rate surfaces are common phenomena for many systems. Sulfur hexafluoride-n-pentanol nucleation was experimentally studied using a flow diffusion chamber. The experimental results for n-pentanol-sulfur hexafluoride at total pressures of 0.10, 0.20, and 0.30 MPa are presented. All experimental conditions were recalculated to correspond to a nucleation temperature of 255.0 K. The observed convoluted lines of In J plotted against In S provide experimental evidence of the existence of multiple nucleation rate surfaces. It can be anticipated that a variety of multiple nucleation rate surfaces, such as presented here, will be detected soon. Obviously, the application of one-component nucleation theory for such systems with multiple nucleation rate surfaces will not be consistent with the data. Separation of the multiple nucleation surfaces reduces the problem to a simpler one-channel treatment of nucleation. It will then be possible to construct a consistent nucleation theory for a given series of compounds.