Droplet-like heterogeneity of aqueous tetrahydrofuran solutions at the submicrometer scale.

A droplet formation in aqueous solutions of tetrahydrofuran (THF) has been experimentally detected at the submicrometer scale using two independent laser diagnostic techniques (dynamic light scattering and laser phase microscopy) and described in terms of THF-water intermolecular hydrogen bonding. It is shown that the nanodroplets have a mean size of 300 nm, their refractive index is higher than that of the ambient liquid, and they are highly enriched with THF molecules. The maximum of light scattering intensity falls within the THF concentration range 2-8 mol. %, which corresponds to the volume number density of the nanodroplets ∼1010-1011 cm-3. A theoretical explanation of forming the nanodroplets with a high content of THF, which is based on a model of dichotomous noise being applied to the so-termed "twinkling" hydrogen bonds and involves spinodal decomposition in the unstable region enclosed within the dichotomous binodal, is proposed. The parameters of hydrogen bonds in the molecular system "water-THF" were found, and the phase diagram of the solution with allowance for cross-linking hydrogen bonds was constructed.

Self-action of ultrasonic beams for biological applications.

Theoretical and experimental investigations of powerful ultrasonic beams self-focusing in liquids are described. Calculations of the conditions to observe self-action as a result of sound-induced heating of liquids are reported. The effects of controlled self-action of ultrasonic waves in high-viscosity liquids are demonstrated in experiments. A hydrodynamic mechanism of the acoustic dispersion technique is developed. The rate of this process, as a function of ultrasound intensity, including the effects of self-focusing and self-transparency, is evaluated.

Mechanism of low-threshold hypersonic cavitation stimulated by broadband laser pump.

A low threshold acoustic cavitation regime was observed for the excitation of hypersonic waves due to a stimulated Brillouin scattering (SBS) mechanism, when the optical pump lies within the uv frequency range. Cavitation occurs if the optical pump bandwidth Delta(+)>>Omega(0), where Omega(0) is the Stokes frequency shift (the hypersonic frequency). In the opposite case (Delta(+)<