Determination of the Frequency Dispersion Region of the Transport Coefficients of Classical Liquids Depending on the Character of Attenuation of Relaxing Flows

We consider the frequency dispersion region of the dynamic shear viscosity coefficient ηs (ω) of simple liquids obtained by the method of kinetic equations, where the equilibrium structure of a liquid is restored according to the diffusion law or exponentially. At a certain choice of the intermolecular interaction potential Φ (|r|) and the equilibrium radial distribution function g0 (|r|), the coefficient ηs (ω) for liquid argon was numerically calculated as a function of the density ρ, temperature T, and frequency ω. The obtained theoretical values of the shear viscosity ηs (ω) are in a satisfactory quantitative agreement with experimental data. It is shown that the frequency dispersion region of ηs (ω) obtained on the basis of the diffusive mechanism, i.e. structural relaxation, is large (~ 105 Hz). In the case of the exponential attenuation of the viscous stress tensor, this region is narrow (~ 102 Hz), which agrees both with acoustic measurements and the results of a phenomenological theory.