Binary N-octanol–sulfur hexafluoride nucleation

Abstract

Recently, the accuracy of vapor nucleation rate measurements has increased substantially. However, when experimental conditions become close to the values to the critical parameters of investigated systems, significant discrepancies were found between the experimental results and theoretical predictions. Some studies have found agreement between results and theory only within a narrow range of nucleation conditions. Therefore, it is appropriate to investigate the nucleation of additional systems to obtain new information to guide nucleation theory development. Alcohols are the most studied class of chemical compounds, but currently there are no experimental data on n-octanol vapor nucleation. The present study is devoted to the investigations of the homogeneous nucleation of the n-octanol in sulfur hexafluoride. Comparison of the critical pressures for binary mixture with the Laplace pressure calculated in the droplet approximation using the bulk liquid surface tension shows that the carrier gas has a more active role in the nucleation than assumed by classical theory. A very high Laplace pressure in the critical embryo is calculated in the droplet approximation. When compared with the highest possible critical pressure for the binary system under investigation, the problems associated with calculating the critical embryo excess energy using the bulk liquid surface tension are revealed. Disagreement of the experimental results with predictions of classical nucleation theory, Dillmann–Meier theory, or any other theory reveals the same basic problems. These results suggest that it is appropriate to consider the general problem of vapor–liquid nucleation in a carrier gas including the estimation of the size and temperature dependence of the critical embryo excess energy as a binary nucleation problem instead of that of a single component. Theories for single-component vapor nucleation should be compared with the truly single-component vapor nucleation experimental results.