Selective solvation effects in phase separation in aqueous mixtures

Selective solvation can be crucial in phase separation in polar binary mixtures (water–oil) with a small amount of hydrophilic ions or hydrophobic particles. They are preferentially attracted to one of the solvent components, leading to a number of intriguing effects coupled to phase separation. For example, if cations and anions interact differently with the two components, an electric double layer emerges at a liquid–liquid interface. The main aim of this paper is to show that a strongly hydrophilic (hydrophobic) solute induces precipitation of water-rich (oil-rich) domains above a critical solute density np outside the solvent coexistence curve.

When a small amount of a hydrophilic salt is added to an aqueous mixture, water droplets enriched with salt precipitate even outside the solvent coexistence curve. When hydrophobic particles are added, oil droplets precipitate.Figure optionsDownload high-quality image (117 K)Download as PowerPoint slideHighlights
► Solvation chemical potential of a solute particle strongly depends on the composition in mixture solvents, so a selective solute strongly influences phase transitions.
► A highly selective solvent can induce phase separation in aqueous mixtures with increasing its concentration above a critical value.
► Precipitated domains are water enriched with hydrophilic salt or oil enriched with hydrophobic solute.