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Current issue   Ukr. J. Phys. 2016, Vol. 61, N 10, p.879-885
http://dx.doi.org/10.15407/ujpe61.10.0879    Paper

Bulavin L.A.1,2, Bilous O.I.1, Svechnikova O.S.1

1 Taras Shevchenko National University of Kyiv
(64/13, Volodymyrs’ka Str., Kyiv 01601, Ukraine)
2 Institute for Safety Problems of Nuclear Power Plants, Nat. Acad. of Sci. of Ukraine
(12, Lysogirska Str., Bld. 106, Kyiv 03028, Ukraine; e-mail: bulavin221@gmail.com,
o_bilous@ua.fm, oksana.svechnikova@gmail.com)

Relaxation Time of Concentration Fluctuations in a Vicinity of the Critical Stratification Point of the Binary Mixture n-Pentanol–Nitromethane

Section: Soft Matter
Original Author's Text: Ukrainian

Abstract: The propagation velocity and the absorption coefficient of ultrasound in a frequency range of 5–2800 MHz in a n-pentanol–nitromethane solution in a vicinity of its critical stratification point from the homogeneous state side have been studied. The research make it possible to reveal the influence of concentration fluctuations on the sound propagation velocity. Three regions of dynamical parameters are analyzed: the mean-field (ωτFL«1), fluctuation (ωτFL»1), and transition (crossover, ωτFL = 1) ones. On the basis of experimental data, the temperature dependence of the concentration fluctuation relaxation time τ(T) is studied, and its magnitude τ0 is determined. The contribution to the fluctuation part of the sound absorption coefficient at high frequencies (ω > 300 MHz), which is connected with the sound scattering by concentration fluctuations near the critical stratification point is estimated.

Key words:  ultrasound velocity, ultrasound absorption, critical stratification point, binary solution, concentration fluctuations, relaxation time.