M. Kosmowska

Sound attenuation, shear viscosity, and mutual diffusivity behavior in the nitroethane-cyclohexane critical mixture

The shear viscosity eta(s), mutual diffusion coefficient D, and ultrasonic attenuation spectra of the nitroethane-cyclohexane mixture of critical composition have been measured at various temperatures near the critical temperature T(c). The relaxation rate of order parameter fluctuations resulting from a combined evaluation of the eta(s) and D data follows power law behavior with the theoretical exponent and with the large amplitude Gamma(o)=(156+/-2)x10(9) s(-1). The ultrasonic spectra have been evaluated in terms of a critical contribution and a noncritical background contribution. The amplitude of the former exhibits a temperature dependence, in conformity with a temperature dependence in the adiabatic coupling constant (|g| = 0.064 near T(c) and 0.1 at T-T(c)=3 K). If the variation of the critical amplitude with T is taken into account the experimental attenuation coefficient data display a scaling function which nicely fits to the theoretical prediction from the Bhattacharjee-Ferrell dynamic scaling model [R. A. Ferrell and J. K. Bhattacharjee, Phys. Rev. A 31, 1788 (1985)].

Non-linear dielectric effect in an ethanol + dodecane critical mixture with minor amounts of ions

A critical binary mixture with a low concentration of ions (tetramethylamonium chloride) was investigated by the non-linear dielectric method. It was observed that the addition of ions increases the critical anomaly of the non-linear dielectric effect. The increase was only observable at low frequencies of the measuring field. Possible explanations are presented and discussed. In spite of the very low concentration of ions, some evidence of crossover from Ising-like to the mean field behaviour was found.

Electric permittivity anomaly close to the critical consolute point of a nitrobenzene + octane liquid mixture.

Electric permittivity and density were measured in a nitrobenzene and octane mixture in the vicinity of the upper critical consolute point. Measurements were conducted in the one-phase region, at the critical concentration. The possibility of stirring in the course of measurements allowed us to check if the density and concentration gradients had any influence on the obtained results. No signs of the presence of the gradients mentioned above were found. Using the data obtained in the reported measurements, different methods of the fitting of the equation describing the permittivity anomaly were tested. The calculation of a reliable value of the critical amplitude, used to estimate the critical temperature shift under the influence of the electric field, was of particular interest. The derivative (∂T(c)/∂E(2)) was found to be (-3.9 ± 0.3) × 10(-16) K m(2) V(-2).