Ps. Doyle et al., RELAXATION OF DILUTE POLYMER-SOLUTIONS FOLLOWING EXTENSIONAL FLOW, Journal of non-Newtonian fluid mechanics, 76(1-3), 1998, pp. 79-110
The relaxation of dilute polymer solutions following stretch in uniaxi
al extensional flow is investigated via Brownian dynamic simulations o
f a flexible freely-draining bead-rod chain. The bead-rod chain simula
tions are compared to Brownian dynamic simulations of a FENE dumbbell
and numerical calculations of a FENE-PM chain. A universal relaxation
curve for the stress decay from steady-state is found by shifting the
results to lie on the curve described by the relaxation of an initiall
y straight chain. For all the models investigated, the initial rapid d
ecay of the polymer stress decreases at a rate which scales for large
Weissenberg number, Wi as Wi(2). Our universal curve is in good qualit
ative and in some cases quantitative agreement with the available expe
rimental data: it is particularly good in predicting decay after stret
ch at the largest strains. We find hysteresis in comparing the stress
versus birefringence during the startup of flow and subsequent relaxat
ion for the bead-rod chain and FENE dumbbell, but not for the FENE-PM
chain. The hysteresis in the latter model is lost in the preaveraging
of the nonlinear terms. The bead-rod model also displays a configurati
on hysteresis. The hysteresis observed in these models is in qualitati
ve agreement with recent experiments involving polystyrene-based Boger
fluids. (C) 1998 Elsevier Science B.V. All rights reserved.