Bilous O. Acoustic and rheological properties of some liquid systems near the critical temperature

The experimental investigations of dynamic viscosity coefficient (hs), acoustical absorption coefficient (aЧf-2) and sound propagation velocity (с) in a range of frequencies from 2,5 MHz to 3000 MHz in a wide range of concentrations and temperatures, including a vicinity of critical temperature (CT), have been carried out in the work. The different by nature liquid systems such as methanol-hexane, methanol-heptane, nitromethane-n-amil alcohol and nitrobenzene-hexane binary solutions and penthilcianbyfenil (5CB) liquid crystal in isotropic phase have been taken as the studying objects. Two acoustic relaxation areas in studied solutions have been found. Low-frequency relaxation area has fluctuation nature, i. e. it is determined by processes of fluctuations formation and decomposition. High-frequency area is caused by internal-molecular processes, which occur in liquid system due to formation and break of bounds between molecules. On the basis of the data on frequency and temperature behavior of acoustical absorption coefficient in a low-frequency range of the temperature and concentration dependence of relaxation times in binary liquid systems have been investigated. This dependence is caused with concentration fluctuations lifetime close to the CT. The obtained data confirm conclusions of the dynamic theory of critical phenomena about asymptotic behavior of the mentioned magnitudes within ranges wtс<<1 and wtс >>1.