Tracer Diffusion and Shear Viscosity in the Liquid–Liquid Critical Region

Abstract

Tracer diffusion coefficients of 3-methylpentane in mixtures of 3-methylpentane–nitroethane have been measured over the entire concentration range above the critical temperature in the range 0.04° ≤ T − Tc ≤ 9.5°C using the diaphragm cell technique. No anomaly was detected. The shear viscosity coefficients were measured across the concentration range for temperatures 0.004°C ≤ T − Tc ≤ 13.5°C by a capillary viscometer. The excess viscosities are compared with the predictions of the Fixman theory and the theory of Kadanoff and Swift. Very close to the critical point the weak divergence predicted by the second theory is observed while at larger values of ΔT Fixman's prediction seems adequate.