THE DYNAMICS OF ULTRADILUTE POLYMER-SOLUTIONS IN TRANSIENT FLOW - COMPARISON OF DUMBBELL-BASED THEORY AND EXPERIMENT

Predictions of the Chilcott-Rallison FENE dumbbell model for polymer c onfiguration in start-up flow of a co-rotating two-roll mill, are comp ared with birefringence measurements in a 40 ppmw solution of high mol ecular weight polystyrene. Two versions of the Chilcott-Rallison model are considered, one with a constant bead friction and the other with bead friction that is assumed to increase in proportion to the end-to- end dimension of the dumbbell. Parameters for the model were determine d via independent experiments. We show that the flow, at this concentr ation level, is unchanged from the form for a Newtonian fluid. Measure ments and predictions of the birefringence are compared at the stagnat ion point of the flow, where a high degree of polymer stretch is possi ble. The Chilcott-Rallison model with constant bead friction, and an a pproximation to the inverse Langevin spring function, gives excellent agreement with the experimental results. (C) 1998 The Society of Rheol ogy.