An atomistic interpretation of viscous flow in liquid metal elements

Abstract

For the microscopic mechanisms of viscous flow, we are still at the age of 1930s when Andrade proposed atoms conveyed momentum to a neighboring drift plane by vibrating across the plane. For the lack of the properties of liquids, the most intriguing part of atomic migration, namely, “friction by transport” that Andrade called the mechanism of viscosity for shortness, remains untackled. In this work, on basis of our atomistic model for liquid diffusion, the process of viscous flow in liquids is examined in view of atom migrations. The friction force exerted on the migration atoms can be estimated from the activation energy of vacancy migration. Accordingly, the instantaneous shear moduli of liquid metal elements and its’ temperature dependence are derived and verified with reported measured data. On this basis, an a priori atomistic calculation of viscosity is presented as a reference considering the unavoidable contamination of turbulent flow in experiment. Finally, the Stokes-Einstein relation is re-examined in terms of the present discussion of liquid viscosity.