Brownian dynamics simulations of linear polymers under shear flow

Brownian dynamics simulations of a polymer chain described by three differe nt 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 ro ds. Model B is a freely jointed chain consisting of finitely extensible non linear elastic (FENE) springs. Excluded volume and hydrodynamic interaction s are not taken into account in either of these two models. Model C is a ch ain with rigid bonds, valence, and torsional angle potentials, excluded vol ume and hydrodynamic interactions. Asymptotic dependencies [eta] similar to (gamma)over dot(-1/3) and [eta] similar to (gamma)over dot(2/3) for the in trinsic viscosity [eta] at large shear rates (gamma)over dot for models A a nd B, correspondingly, have been obtained. Asymptotic dependencies for the first normal stress coefficient Psi(1) similar to (gamma)over dot(-4/3) do not depend on the particular choice of model. At intermediate shear rates [ eta] similar to (gamma)over dot(-1/2) is followed for all models. Scaling d ependencies 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 inc reasing shear rate and reveal evidence of the end-to-end vector flipping be tween orientations parallel and antiparallel to the flow direction. (C) 199 9 American Institute of Physics. [S0021-9606(99)50126-8].