Abstract
A torsion-oscillator viscometer has been constructed for the measurement of the viscosity of fluids near both liquid-vapor and liquid-liquid critical points. This viscometer has a resolution of ±0.2% and operates at a low frequency (0.6 Hz) and a very low shear rate (0.05 Hz). Thus, it can be used closer to critical points than other viscometers before encountering the non-Newtonian phenomena associated with critical slowing down. This viscometer was used to study the viscosity anomaly near the consolute point of mixtures of methanol and cyclohexane along paths of constant pressure and paths of constant volume at temperatures spanning the range 10−5 < (T-T c)/T c<10−2. The data are consistent with a simple, power-law divergence of the viscosity with a multiplicative background characterized by an apparent exponent y≈0.041. Recent theoretical estimates for y are near 0.033. If the data are to be fit with the theoretical value of y, one must simultaneously restrict the range of the data and introduce additional unphysical parameters into the fitting function.
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Berg, R.F., Moldover, M.R. Viscosity measurements near a critical point using a novel torsion oscillator. Int J Thermophys 7, 675–686 (1986). https://doi.org/10.1007/BF00502399
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DOI: https://doi.org/10.1007/BF00502399