MODEL FOR MELT FRACTURE INSTABILITIES IN THE CAPILLARY-FLOW OF POLYMER MELTS

We model the capillary flow of a polymer melt, incorporating a stick-s lip boundary condition at the wall. The boundary condition is enforced by a phase-field model for the local state of the polymer, which desc ribes the kinetics of a first-order transition. We numerically solve t he linearized Navier-Stokes equations, coupled to this prescribed boun dary condition and to a Maxwell model for viscoelasticity. In various regimes, the model exhibits steady flow, periodic oscillations, and mo re complicated spatiotemporal structures; which can be observed experi mentally.