Ferdinand Volino | Searcharxiv

arXiv2023

A novel approach for modeling the non-Newtonian behavior of simple liquids: application to liquid water viscosity from low to high shear rates

The aim of this paper is to present a modeling for the rheological behavior of simple liquids as a function of the amplitude of the imposed shear stress or strain. The elastic mode theory (Ref. 6) is first generalized to take into account the fact that during a flow experiment, mechanical energy is injected in a system initially at thermodynamic equilibrium. This generalized theory can be seen as a particular aspect of the general problem of perturbation by the measurement, associated with that of the coupling between fluctuation and dissipation. This generalization leads to a "finitary" character of the model. It is then combined with the inertial mode theory (Ref. 7). The formalism thus obtained allows to model the rheological behavior of liquids over a wide range of velocity gradients, including the intermediate narrow range corresponding to the Newtonian regime. As experimental tests, viscosity measurements with two kinds of moving rotor rheometers were performed. Only data obtained with liquid water at room temperature are presented and quantitatively analyzed here. It is also shown that liquid n-octane exhibits the same qualitative behaviors as those of liquid water. In the appendices, connection of this theory with quantum mechanics and turbulence phenomena are discussed, and the notion of viscous mass is introduced.

cond-mat.soft↗

arXiv2022

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

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 predict 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 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.

cond-mat.soft↗