Laser Diagnostics of the Mesoscale Heterogeneity of Aqueous Solutions of Polar Organic Compounds

A mesoscale droplet phase, which is spontaneously formed in aqueous solutions of some polar organic compounds, has been experimentally investigated by methods of dynamic light scattering and laser phase microscopy. It is shown that tetrahydrofuran and tert-butanol aqueous solutions demonstrate a strong peak of light scattering intensity in the range of molecular concentrations of about 0.02 to 0.08, which corresponds to inhomogeneities with a characteristic size of about 100 nm. These liquid droplets are enriched with molecules of dissolved substance. A similar light scattering peak for aqueous solutions of glycerol and ethylene glycol is less pronounced. A theoretical model of the phase separation of binary solutions with twinkling (i.e., existing for a finite time) intermolecular hydrogen bonds is developed. The model predicts the existence of an additional low-concentration light scattering peak near the spinodal of the solution free of hydrogen bonds. A characterization of solutions according to the numerical values of twinkling hydrogen bond parameters is outlined.