Formation of nano-mixture comprising hydrophobic solute and water: determination of their anomalous precipitation and pseudo-dissolution behaviours by adsorption isotherm measurements.

In this study, a nano-mixture formed in nanometre-scale spaces using water and insoluble solutes was investigated. The adsorbed phase formed a system consisting of a small number of molecules, almost all of which existed near the solid surface. Consequently, the physical properties of nano-mixtures, such as solubility, are expected to differ significantly from those of bulk solutions. We investigated the formation of nano-mixtures by measuring the physical-adsorption isotherms of solvents on porous materials to which solutes were loaded. The dynamic behaviour of the solute molecules was evaluated using 1H nuclear magnetic resonance spectroscopy. These results demonstrated that dibenzyl, a nonpolar organic molecule insoluble in bulk water, could be dissolved in water within a silica nanospace of 3.8 nm diameter. This study elucidated the unique properties of nano-mixtures and demonstrated the importance of systematically understanding them.