Viscometric functions for FENE and generalized Lennard-Jones dumbbell liquids in Couette flow: molecular dynamics study

Abstract

We report new macro-rheological results extracted from non-equilibrium molecular dynamics (NEMD) simulations of Couette flow. We investigate atomic liquids for new state points, and in addition two types of dumbbell liquids: (1) finitely extensible nonlinear elastic (FENE) and (2) newly defined generalized Lennard-Jones (GLJ), up to a nondimensional shear rate of 15. The dumbbell liquids exhibit shear thinning, non-zero first and second normal stress differences, and volumetric dilatancy. These effects are weakly sensitive to details in shape of the intra-molecular potentials, and to the dominant frequency associated with vibrations of dumbbells. However, the Newtonian viscosity of dumbbell liquids strongly depends on the size of dumbbells. The onset of shear thinning of FENE and GLJ dumbbells is delayed to higher shear rates in comparison with atomic liquids. In general, for the entire investigated region, we see that dumbbells are slightly more elastic than atomic liquids.