The shear viscosity and self-diffusion in ordinary water

TL;DR

This paper analyzes the shear viscosity and self-diffusion in water across all states from the triple point to the critical point, using models based on molecular interactions and hydrodynamic modes.

Contribution

It introduces a detailed analysis of water's transport processes, applying a friction-based approach for shear viscosity and a dual contribution model for self-diffusion.

Findings

Shear viscosity in water is similar to that in argon, dominated by molecular layer interactions.

Self-diffusion involves nano-scale vortex modes and molecular intermixing, accurately described by Einstein's formula.

Behavior of viscosity and diffusion is characterized along vapor-liquid coexistence and isotherms.

Abstract

The paper is devoted to a detailed analysis of the two important transport processes - the kinematic shear viscosity and the self-diffusion - for all states of liquid water from the triple point to the critical point. Our approach to the shear viscosity is grounded on friction effects between the two nearest molecular layers shifting relative to each other. In this relation, the nature of the shear viscosity in water is fully similar to that in argon. The contribution, caused by interlayer displacements of molecules, is assumed to be negligibly small. The behavior of the kinematic shear viscosities of water is investigated in detail in the two characteristic directions: the vapor-liquid coexistence curve and isotherms. As for argon, it is assumed that the self-diffusion in water is formed by the two main contributions, caused by the molecular transport by nano-scale vortex hydrodynamic modes and collective intermixing of molecules on molecular scales. The mechanism of the second type is with good accuracy described by the Einstein formula with a hard-core radius of a molecule determined from analysis of the shear viscosity of water.