An experimental and simulation study of dilute polymer solutions in exponential shear flow: Comparison to uniaxial and planar extensional flows

The rheological properties of dilute polymer solutions in exponential shear , uniaxial, and planar extensional flows are compared using Brownian dynami cs simulations of both freely draining, flexible bead-rod and bead-spring c hains. We introduce a novel stress function for exponential shear which use s the extinction angle chi to take into account the orientation of the chai n as it aligns in the flow. Comparing this new stress function during start up and relaxation in exponential shear with tau (11)- tau (22) in planar ex tensional flow and tau (11)- 1/2( tau (22)+ tau (33)) in uniaxial extension al flow, we find that for both models there is a quantitative agreement amo ng the three different flows over a large range of Wi, strain, and chain le ngth. Furthermore, the distributions of maximum extension show a microstruc tural equivalence between ensembles of chains in all three flows up to stra ins of 3 or 4 at all values of Wi simulated. Finally, we show three compari sons between experiment and simulation of the various flows: (a) simulation s and exponential shear experiments of a polyisobutylene/polybutene Boger f luid, (b) simulations and uniaxial extension data from literature, and (c) exponential shear and planar extensional data of a low-density polyethylene melt from literature. (C) 2001 The Society of Rheology.