Brownian dynamics simulations of linear polymers under shear flow

Abstract

Brownian dynamics simulations of a polymer chain described by three different models under the influence of a shear flow have been performed. Model A is a freely jointed Kramers chain consisting of beads connected by rigid rods. Model B is a freely jointed chain consisting of finitely extensible nonlinear elastic (FENE) springs. Excluded volume and hydrodynamic interactions are not taken into account in either of these two models. Model C is a chain with rigid bonds, valence, and torsional angle potentials, excluded volume and hydrodynamic interactions. Asymptotic dependencies [η]∼γ̇−1/3 and [η]∼γ̇−2/3 for the intrinsic viscosity [η] at large shear rates γ̇ for models A and B, correspondingly, have been obtained. Asymptotic dependencies for the first normal stress coefficient Ψ1∼γ̇−4/3 do not depend on the particular choice of model. At intermediate shear rates [η]∼γ̇−1/2 is followed for all models. Scaling dependencies of rheological properties on molecular weight have been studied. Results of the simulations show that chains are not fully stretched even at extremely high shear rates but form rather compact anisotropic objects. Correlation functions of the chain end-to-end vector relax quicker with increasing shear rate and reveal evidence of the end-to-end vector flipping between orientations parallel and antiparallel to the flow direction.