Stability of the interface between two dynamic phases in capillary flow of linear polymer melts

Results of previous work¹ on a theoretical explanation of the “spurt effect” in polymer melt flow are extended. A modified Doi—Edwards liquid is shown to support axisymmetric traveling waves on an interface between high and low shear-rate phases in capillary flow. The stability of these perturbations is found to be governed by normal stress effects and may be related to certain types of melt fracture. Observed effects of varying the capillary length are explained qualitatively.