Study of the submicron heterogeneity of aqueous solutions of hydrogen-bond acceptor molecules by laser diagnostics methods

Three independent experimental laser techniques (dynamic light scattering, nanoparticle tracking analysis, and laser phase microscopy) have been used to find and quantitatively characterize a lowconcentration domain of existence for the droplet-stratified phase in an aqueous solution of tetrahydrofurane (THF) molecules acting as hydrogen bond acceptors. The concentration and temperature dependences of the light scattering intensity and droplet sizes in the solution have been measured. It is shown that the nanodroplets found have a higher light refractive index than that of water and that they are highly enriched with THF molecules. An estimation of the volume number density of 300-nm droplets, based on the data obtained, yields a value on the order of 10(8) cm(-3). The droplet lifetime is limited by the effect of the buoyancy force and amounts to several days. A crossover is found in the temperature dependence of scattering intensity in the droplet phase, which indicates possible interaction of two order parameters: the THF concentration and the number of hydrogen bonds of THF and H2O molecules. A model stochastic theory is proposed to describe the stratification of solutions with cross hydrogen bonds, which predicts stratification in the low-concentration range adjacent to the spinodal decay region.