Viscosity of Critical Mixtures

Abstract

A theory is given of the sharp viscosity rise in mixtures in the critical mixing region. Good agreement with the experimental dependence of viscosity on composition and temperature is found. The method involves a calculation of the entropy production through diffusion which results when a mixture in a state of composition fluctuation is caused to have a velocity gradient. The long wavelength part of the spectrum of composition fluctuations is intense and very easily distorted by a velocity gradient in the critical region. The return to uniform composition through diffusion dissipates energy, and the loss is interpreted as an excess viscosity. It is shown that this method, which requires no knowledge of the intermolecular potential but only of the long-range part of the radial distribution function, correctly gives the viscosity of a dilute 1–1 electrolyte.