Water Structure withinTernary Solvents Suggests NanophaseFormation

Abstract Water’s unique solvating properties and its interactions with hydrophobic surfaces play crucial roles in various chemical processes ranging from self-assembly to phase separation. This study investigates the structure and hydrogen bonding of water in ternary solvent systems composed of water, a cosolvent (acetone, dimethylformamide, or dimethyl sulfoxide), and an oil (2-hexanone or 2-pentanone) to reveal how solvent organization changes upon oil addition. Using Raman spectroscopy coupled with multivariate curve resolution, we probe changes in hydrogen bonding as a function of ternary composition. Counterintuitively, replacing the cosolvent with oil while maintaining constant water levels reduces the volume of perturbed water within hydrophobic hydration shells. We also find a higher population of dangling hydroxyl groups upon oil addition. We propose that these results are indicative of the formation of nanoscale, oil-rich aggregates (nanophases) dispersed in water. This work offers insights into the role of hydrophobic hydration in ternary solvents, contributing to our understanding of nanophase formation, solvent behavior, and interfacial phenomena in complex mixtures.