title: Molecular physics of a polymer engineering instability: experiments and computation.
abstract: Entangled polymer melts exhibit a variety of flow instabilities that limit production rates in industrial applications. We present both experimental and computational findings, using flow of monodisperse linear polystyrenes in a contraction-expansion geometry, which illustrate the formation and development of one such flow instability. This viscoelastic disturbance is observed at the slit outlet and subsequently produces large-scale fluid motions upstream. A numerical linear stability study using the molecular structure based Rolie-Poly model confirms the instability and identifies important parameters within the model, which gives physical insight into the underlying mechanism. Chain stretch was found to play a critical role in the instability mechanism, which partially explains the effectiveness of introducing a low-molecular weight tail into a polymer blend to increase its processability.
authors.affiliation: Department of Chemical Engineering, University of Cambridge, Cambridge CB2 3RA, United Kingdom.
authors.forename: D G
authors.initials: DG
authors.lastname: Hassell
authors.forename: M R
authors.initials: MR
authors.lastname: Mackley
authors.forename: M
authors.initials: M
authors.lastname: Sahin
authors.forename: H J
authors.initials: HJ
authors.lastname: Wilson
authors.forename: O G
authors.initials: OG
authors.lastname: Harlen
authors.forename: T C B
authors.initials: TC
authors.lastname: McLeish