We examine phase separation in aqueous mixtures due to preferential solvation with a low-density solute (hydrophilic ions or hydrophobic particles). For hydrophilic ions, preferential solvation can stabilize water domains enriched with ions. This precipitation occurs above a critical solute density $n_{\text{p}}$ in wide ranges of the temperature and the average composition, where the mixture solvent would be in a one-phase state without solute. The volume fraction of precipitated domains tends to zero as the average solute density $\overline{n}$ is decreased to $n_{\text{p}}$ or as the interaction parameter $\chi$ is decreased to a critical value ${\chi }_{\text{p}}$. If we start with one-phase states with $\overline{n}>n_{\text{p}}$ or $\chi >{\chi }_{\text{p}}$, precipitation proceeds via homogeneous nucleation or via heterogeneous nucleation, for example, around suspended colloids. In the latter case, colloid particles are wrapped by thick wetting layers. We also predict a first-order prewetting transition for $\overline{n}$ or $\chi$ slightly below $n_{\text{p}}$ or ${\chi }_{\text{p}}$ for neutral colloids.

• Received 8 October 2010

DOI:https://doi.org/10.1103/PhysRevE.82.051501