Numerical simulation of the transient flow of branched polymer melts through a planar contraction using the 'pom-pom' model

Calculations of the transient flow of branched polymer melts through a plan ar 4: 1 contraction and along a channel are presented. The polymer is model led as a monodisperse suspension of 'pom-pom' molecules using the constitut ive equation developed by McLeish and Larson [T.C.B. McLeish, R.G. Larson, J. Rheol. 42 (1998) 81-110], which provides a direct Link between the molec ular topology and the flow properties of the melt. The branching produces a n enhancement in the size of the upstream vortex, similar to that observed experimentally with branched polymer melts. The effect arises from the wide ly differing responses in shear and extensional flow, and is predicted to b e sensitive to time, degree of branching and Weissenberg number. (C) 1999 E lsevier Science B.V. All rights reserved.