Comments on Friction Constant Formalism

Abstract

Expressions for the molecular friction constant based on the acoustic continuum and small-step diffusion models have been compared with experimental data. The integral describing ζ was evaluated by assuming an (n, m) potential and by substituting internal energy and pressure for terms involving integrals of the radial distribution function. The experimentally estimated values of the friction constant, from which a hard-core contribution is removed, do not yield consistent or realistic values of the potential parameters n and m. The successful prediction of the coefficient of thermal conductivity and shear viscosity for liquid argon using the Rice—Allnatt theory is based on the extrapolation of experimental data for self-diffusion. Statistical analysis of these data indicates that they do not permit a reliable test of the theory. Predicted values of the bulk viscosity coefficient of liquid argon are 40%—50% lower than recent experimental data, and the pressure dependence of the bulk viscosity coefficient at constant density calculated from the Rice—Allnatt theory is of the wrong sign.