Ultrasonic Study of Nitro‐Benzene/Isooctane Mixtures near the Critical Consolute Point

Abstract

The absorption and velocity of ultrasound are measured in a critical mixture of nitro‐benzene and isooctane (2,2,4‐trimethyl‐pentane) as function of the temperature difference (T–Tc) in the homogeneous phase region. The critical data of the system having an upper critical point are: critical temperature Tc = 29.16°C; critical composition ync = 0.525 (mass fraction of nitro‐benzene). The experiments are carried out in the temperature range 0.3 K ≤ (T–Tc) ≤ 21.8 K at seven frequencies between 9 MHz and 45 MHz. Four mixtures with off‐critical compositions and the pure components are also studied. — The sound absorption of the critical mixture is analysed in terms of the Bhattacharjee‐Ferrell theory. At the critical temperature the frequency dependence of ultrasound absorption is in agreement with the predictions of this theory. The data obtained at temperatures away from the critical temperature collapse on a single scaling curve when plotted as function of a reduced frequency given by the theory. Not all of the input data for the calculation of the temperature‐independent coefficient ω0 of the temperature‐dependent characteristic relaxation frequency are available for that system. Therefore, the coefficient ω0 is used as free parameter in a fitting procedure of the theoretical scaling function to the experimental scaling function. The best fit is obtained with ω0 = 15 MHz. The agreement between theory and experiment is good and supports the universality concept of the critical acoustic behavior.

Annihilation of o-Positronium in the Vicinity of the Critical Mixing Point

“…results in large and long-living concentration fluctuations impeding most of macroscopic properties of such binary mixtures. Some of the quantities, as light scattering [1][2][3][4][5], non-linear dielectric effect [6][7][8], absorption of ultrasonic waves [9][10][11] exhibit strong critical anomalies while others, as density [12] or electric permittivity [13,14] -weak ones. Many critical properties could be qualitatively predicted when regarding a mixture in the vicinity of critical point as an inhomogeneous one.…”

Composition fluctuations in a non-critical binary polymer blend studied by ultrasonic and light scattering experiments

“…In the absence of mode coupling effects, the measured G(q) ¼ Dq 2 is related to the mutual diffusion coefficient D as given by eqn. (4).…”

“…1 The ultrasonic behaviour of critical fluids has been studied extensively in the last four decades, both experimentally and theoretically. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The experimental data are explained by the coupling of the sound wave with critical order parameter fluctuations. The ultrasound attenuation in binary mixtures can be described by the following mechanism: Because of alternate adiabatic compression and expansion of the fluid the local temperature and the pressure dependent critical temperature will change.…”

Concentration Fluctuations in Ethanol/Dodecane Mixtures. A Light-Scattering and Ultrasonic Spectroscopy Study

“…[23][24][25][26][27][28][29][30] Ultrasonic spectra have been measured for several binary mixtures and have been compared with theoretical scaling functions. [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] For nonassociating liquids the theoretical predictions are good but often do not exactly describe the measured ultrasonic attenuation. For this reason, much interest is directed toward crossover corrections for scaling, enabling the theoretical approaches to be more adequately used apart from the critical point where large noncritical contributions to the sonic spectrum may exist.…”