Molecular content and structure of aqueous organic nanodroplets from the vapor-liquid nucleation study of the water/n-nonane/1-alcohol series

Prompted by a previous finding of unusual mixing behavior for the critical clusters involved in the vapor-liquid nucleation of the ternary water/n-nonane/1-butanol mixture, atomistic simulations employing the AVUS-HR technique were carried out to extend such investigations to include both shorter and longer alcohols, namely, the water/n-nonane/CiH2i+1OH mixture with i = 2, 4, 6, and 8. It is clear from this extensive investigation that the miscibility between water and n-nonane can be further improved by increasing the chain length of the alcohol (surfactant). In fact, for the water/n-nonane/1-octanol mixture at an intermediate gas-phase activity composition, the nucleation can proceed via fully mixed critical nuclei containing a roughly equal amount of all three components, which is in contrast to the dominantly binary-like nucleation channels observed for such mixtures involving shorter alcohols. Structural analysis revealed that these mixed nuclei take on a multilayered structural motif of the core-shell (water-alcohol) type with n-nonane distributed outside, forming an additional layer, more or less uniformly, compared to the one-sided deposition found for systems involving shorter alcohols. This structure provides a microscopic origin for the enhanced miscibility of water with n-nonane observed in the presence of 1-alcohol. These results may also have important implications for atmospheric organic aerosols.