Critical Behavior and Crossover Effects in the Properties of Binary and Ternary Mixtures and Verification of the Dynamic Scaling Conception

Abstract

Ultrasonic attenuation spectra in the frequency range between 180 kHz and 500 MHz, dynamic light scattering and shear viscosity measurements of a variety of liquids exhibiting a demixing point have been measured are discussed with respect to their critical properties. Evaluating the experimental data for liquid mixtures of critical composition particular attention is given to the applicability of Bhattacharjee-Ferrell dynamic scaling model and to corrections for the effects from the crossover from Ising to mean-field behavior. Three types of critical liquids have been considered: binary mixtures without complex background contributions in their ultrasonic spectra (n-pentanol-nitromethane, nitroethane-cyclohexane, nitroethane-3-methylpentane, methanol-hexane, and ethanol-dodecane), binary mixtures with additional relaxations in the time domain of critical fluctuations (2,6-dimethylpyridin-water, isobutoxyethanol-water, triethylamine-water), and ternary mixtures with concentrations selected along the plait-point line (nitroethane-3-methylpentane-cyclohexane). With the latter system interest is particulary directed to the dependence of critical parameters upon the concentration of a constituent. The results clearly demonstrate that the Bhattacharjee-Ferrell theory and the crossover theory nicely represent the experimental ultrasonic attenuation spectra as well as the shear viscosity and dynamic light scattering data. This is true for both binary and ternary mixtures. It is shown that use of the Bhattacharjee-Ferrell model for the analytical representation of the critical part in the ultrasonic attenuation spectra of more complicated binary systems such as isobutoxyethanol-water and 2,6-dimethylpyridin-water allows for a favourable description of further relaxation terms. With the assumption that the contributions from chemical relaxations contribute additively to the critical contributions the ultrasonic spectra as well as the scaling function of the critical systems can be well represented in terms of the Bhattach arjee-Ferrell model. In the case of triethylamine-water it is demonstrated that the experimental scaling function agrees with the Bhattacharjee-Ferrell function only, when both Debye relaxation terms are allowed slow down near the critical point. The experimental results are complemented by density and sound velocity measurements.