Critical phenomena in associative binary liquid mixtures with miscibility gap

Abstract

Measurements of the temperature and frequency dependence of ultrasonic absorption (frequency range 9 MHz<f<45 MHz) of an associative (chemically reactive) binary liquid mixture of critical composition — an isobutyric acid/water mixture — are analyzed in terms of the dynamic scaling theory of critical ultrasonic attenuation proposed by Ferrell and Bhattacharjee. The system-specific critical amplitude of relaxation rate of local composition fluctuations is known for that system from independent measurements. The data do not scale as expected. A temperature- and frequency-dependent ultrasonic background attenuation is observed. Measurements of ultrasonic attenuation of the same system in a broad frequency range (0.2 MHz<f 400 MHz) carried out by Kaatze et al. (J. Phys.Chem. 93 4955 (1989)) show a broad frequency spectrum of relaxation times. The low-frequency part of this spectrum of relaxation times observed away from the critical temperature is shifted to lower relaxation frequencies approaching the critical temperature. Its principle relaxation time increases in a characteristic manner. Data obtained for two other associative binary liquid mixtures with miscibility gap — 2,6-dimethyl pyridine/water and 2-butooxyethanol/water — show similar effects.