Shear Viscosity of Hexane+Tetradecafluorohexane near the Upper Critical Endpoint

Abstract

AbstractThe shear viscosity of hexane+tetradecafluorohexane has been determined from five Kelvins below the upper critical solution temperature Tc – in the region of limited miscibility – to 19 Kelvins above Tc – in the region of total miscibility. The results show a critical anomaly described by a critical expression η = A exp (B/T)ϵ−y with a multiplicative amplitude or background term η0 = A exp (B/T) and a weakly anomalous term ϵ−y, where ϵ is the reduced temperature response function |T − T|/Tc calculated with Tc = 22.385°C, and the critical exponent y takes the universal value 0.040 predicted by the mode‐mode and renormalisation group theories. The measured viscosities show a definite but small dependence on shear gradient. The shear gradient dependence is entirely described by the Oxtoby treatment which yields an estimate of the critical amplitude of the correlation length ξ0 = (5.5 ± 1.5) Å in fair agreement with the light‐scattering value of Skripov et al. of (3 ± 1) Å. The ratio of the limiting amplitudes along the isochoric path and the coexistence path is 0.946 ±0.005, close to that predicted by Calmettes, 0.950.