Ultrasonic investigation of critical phenomena in the binary system triethylamine–water

The acoustic velocity and absorption have been measured in a series of triethylamine–water mixtures, with special emphasis on the region near the consolute point at XH2O=0.921 and 18.23°C. The frequency range from 1 to 27.3 MHz and temperature range from −2 to 20°C have been explored. The ’’effective’’ absorption and dispersion (observed values corrected for noncritical high-frequency contributions) are compared to Kawasaki–Mistura mode-coupling theories. Neither version of this theory is adequate to describe the experimental data, but it is possible to fit the data empirically by introducing two constant-frequency relaxations in addition to a critical mode-coupling contribution. One of these additional relaxations may be related to the structural relaxation of large hydration complexes. The nature of the other is unclear, but it may be an artifact of the fitting procedure indicative of the inadequacy of the critical contribution.