Simple fluids like for instance aqueous solutions of common hydrophilic well soluble small organic molecules, inorganic salts or mixtures of water with other freely miscible liquids appear to be not so simple. Long-lived mesoscale (larger than molecular scale but smaller than macroscopic scale, typically ~ 100nm) structures/inhomogeneities were evidenced in these systems by methods of static and dynamic light scattering [1]. Kinetics of the formation of these structures upon mixing was also investigated [2]. The time scale on which these mesoscale structures develop in various systems varies from seconds to days. A detailed classification of systems with respect to the capability of formation of such structures was performed (almost 100 different solute/solvent pairs) [3]. Very recently [4], it was possible to visualize these structures as well as their Brownian motion by optical microscopy in the laser beam. It was also proved that these are not nanobubbles [4]. The mystery of the origin of such mesoscale structures was successfully revealed so far in one class of systems [5]. It was proved that mesoscale structures in alcohol/water mixtures originate from mesophase separation of minority components. Chemical compounds used in everyday life and research practice (like for instance alcohols) are in fact multicomponent mixtures of the main component and minority components (unwanted admixtures, impurities). Upon mixing with water, minority components of mainly hydrophobic character (initially molecularly dissolved in alcohol) segregate into well-defined long-term stable mesoscale structures (nanoparticles or rather nanodroplets). A new term of “mesoscale solubility” can be introduced.
[1] M.Sedlák, J.Phys.Chem. B, 110 (9), 4329 - 4338, 2006; [2] M.Sedlák, J.Phys.Chem. B, 110 (9), 4339 - 4345, 2006; [3] M.Sedlák, J.Phys.Chem. B, 110 (9), 13976 - 13984, 2006; [4] M.Sedlák, D.Rak, J.Phys.Chem B, 117 (8), 2495–2504, 2013; [5] M.Sedlák, D.Rak, J.Phys.Chem B, 118 (10), 2726–2737, 2014
