Nonlinear flow behavior and shear-induced structure of fluids

Abstract

The viscous behavior of fluids becomes nonlinear or non-newtonian, when the shear rate is larger than the reciprocal of a characteristic relaxation time. The method of nonequilibrium molecular dynamics (NEMD) is introduced with special emphasis on simulations of a plane Couette flow. Procedures to extract rheological properties, such as the (non-newtonian) viscosity, normal pressure differences as well as information on shear flow induced structural changes, are discussed. Firstly, fluids composed of spherical particles are considered. This comprises simple liquids and dense colloidal dispersions, where the states far away from equilibrium studied in NEMD are accessible in experiments. Secondly, as an axample for complex fluids, polymeric melts are investigated.