Combined Brownian dynamics and spectral simulation of the recovery of polymeric fluids after shear flow

The constrained recovery of polymeric fluids following cessation of steady shear flow is studied using linear bead-spring chain models for dilute polymer solutions and the Curtiss-Bird model for polymer melts. Brownian dynamics simulation techniques are combined with a spectral method for solution of the, continuum equation of motion. The shear stress required to solve the continuum equation is computed directly from ensemble averages over internal configurations of model molecules, thereby eliminating the need for a closed-form constitutive equation. Simultaneous solution of the equation of motion for actual fluid velocities obviates the linear velocity profile assumption used in previous studies of constrained recoil. For each of the models examined in the present work, a maximum was observed in the overall recovery with increasing steady-state shear rate. These maxima are an inherent consequence of the polymer models' shear thinning behavior but are more pronounced if the assumption of a linear velocity profile is relaxed.