Critical exponent for the viscosity of four binary liquids

Published: September 15, 1988


Robert F. Berg, Michael R. Moldover


We have measured the viscosity of four binary mixtures near their consolute points: (1) methanol + cyclohexane, (2) isobutyric acid + water, (3) nitroethane + 3-methylpentane, and (4) 2-butoxyethanol + water. The viscosity data are consistent with the power-law divergence: eta ~ |T- Tc|^-y, with an apparent viscosity exponent in the range 0.0404 < y < 0.0444. Recent theoretical estimates for yare near 0.032, which is outside the experimental range. The value of y is independent of whether the critical point is an upper or a lower consolute point and of whether the approach toward Tc is at constant pressure or at constant volume. Our torsion oscillator viscometer is unique in its simultaneous low frequency ( ~ 1 Hz) and low shear rate ( -0.1 s-1), allowing its use close to the critical point before encountering non-Newtonian fluid behavior associated with critical slowing down. Nevertheless, we find quantitative evidence for viscoelasticity near the critical point.
Citation: Chemical Physics
Volume: 89
Pub Type: Journals
Created September 15, 1988, Updated February 17, 2017