A novel general modeling of the viscoelastic properties of fluids: Application to mechanical relaxation and low frequency oscillation measurements of liquid water

Abstract

The aim of this paper is to calculate the time dependence of the mean position (and orientation) of a fluid particle when a fluid system at thermodynamic equilibrium is submitted to a mechanical action. The starting point of this novel theoretical approach is the introduction of a mechanical energy functional. Then using the notions of inertial modes and action temperature, and assuming a mechanical energy equipartition principle per mode, the model predicts the existence of a dynamic phase transition where the rheological behavior of the medium evolves from a solid-like to a liquid-like regime when the mechanical action is increased. The well-known Newtonian behavior is recovered as the limiting case. The present modeling is applied to the analysis of recent liquid water viscoelastic data pointing out a prevalent elastic behavior in confined geometry. It is demonstrated that the model makes it possible to understand these data in a coherent and unified way with the transport properties (viscosity and self-diffusion coefficient). It is concluded that any finite volume of fluid at rest possesses a static shear elasticity and should therefore be considered as a solid-like medium.