  Water-alcohol mixtures exhibit many abnormal physicochemical properties, the
origins of which remain controversial. Here we use transmission electron
microscopy (TEM), nanoparticle tracking analysis (NTA), and atomic force
microscopy (AFM) to study ethanol-water mixtures. TEM reveals mesoscopic
clathrate structures with water molecules forming a crystalline matrix hosting
a high density of tiny cells. The presence of these mesoscopic clathrate
structures is further supported by a refractive index of 1.27+-0.02 at 405 nm
measured via NTA and the hydrophilic nature of the mesoscopic structures
implied by AFM observations, explaining many long-standing puzzles related to
water-alcohol mixtures.
