The viscosity anomaly near the critical consolute point of the ionic ethylammonium nitrate-n-octanol mixture

Abstract

Measurements of the temperature dependence of the shear viscosity of the ionic binary mixture ethylammonium nitrate in n-octanol near the critical consolute point are reported. The kinematic viscosity is measured with a capillary viscometer in the range of reduced temperature 3×10−5≤t=(T−Tc)/Tc≤6.2×10−2. The temperature dependence of the density is measured by a volume dilatometer. No critical density anomaly is observed within the temperature range 5×10−4≤t≤4×10−2. Shear viscosity data are consistent with a power law divergence η=η0 (Qξ0)−y/νt−yF predicted by the mode-coupling and the dynamic renormalization group theories. The value of the critical exponent y agrees with the theoretical value y=0.032 when the critical temperature Tc is fixed at the experimental value. When Tc is set as a free parameter the fits give 0.0385≤y≤0.0438, depending on the forms chosen for the background viscosity η0 and the crossover function F. Estimation of the wave number Q is found in agreement with data obtained for neutral fluids.