Molecular, brownian and diffusive dynamics: Applications to viscous flow

Abstract

This report is an attempt to reconcile the macroscopic and microscopic views of rheology. Some essential relationships in non-equilibrium molecular dynamics, MD, are derived. These relate the stress response of a fluid to an arbitrary strain rate in terms of time correlation functions linking the stress in an equilibrium ensemble and the stress in the perturbed ensemble. It is shown how these expressions can be made use of in applied statistical mechanics via MD. There is a chapter on algorithmic implementation of these equations. An overview of the behaviour of simple fluids under non-Newtonian shear rates is given, summarising the work to date.

Recent extensions of this approach to multi-component macromolecular suspensions is given. The Strict Langevin equation representing the motion of the macromolecules is combined with the Lees-Edwards shear flow algorithm of MD. This leads to Brownian and diffusive dynamics schemes that reproduce the essential rheology of these systems.