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

L.A. Bulavin, O.I. Bilous, O.S. Svechnikova
2016 Ukrainian Journal of Physics  
PACS 62. 60.+v; 62.80.+f 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 ( FL ≪ 1), fluctuation ( FL ≫ 1), and
more » ... FL ≫ 1), and transition (crossover, FL = 1) ones. On the basis of experimental data, the temperature dependence of the concentration fluctuation relaxation time ( ) is studied, and its magnitude 0 is determined. The contribution to the fluctuation part of the sound absorption coefficient at high frequencies ( > 300 MHz), which is connected with the sound scattering by concentration fluctuations near the critical stratification point is estimated. K e y w o r d s: ultrasound velocity, ultrasound absorption, critical stratification point, binary solution, concentration fluctuations, relaxation time. c ○ L.A. BULAVIN, O.I. BILOUS, O.S. SVECHNIKOVA, 2016 the critical point, FL . This parameter can be determined with the help of various, in particular, acoustic methods [9]. The inherent distinction and the undoubted advantage of acoustic spectroscopy consist in the opportunity to study both static properties of the system (e.g., the velocity of sound propagation) and dynamical ones (e.g., the coefficient of sound absorption, which makes it possible to determine relaxation times in the system). The values of corresponding relaxation times for order parameter fluctuations, FL , can be obtained by means of various experimental methods (nuclear magnetic resonance, dielectric spectroscopy, neutron scattering, light scattering, etc). However, the results obtained with their help can differ from one another by several orders of
doi:10.15407/ujpe61.10.0879 fatcat:4vlpoqmnwbbchds3yjy56ixvpm