title: New light on old wisdoms on molten polymers: conformation, slippage and shear banding in sheared entangled and unentangled melts.
abstract: The flow of viscoelastic materials is usually interpreted as resulting from intramolecular properties. Typically, the non-linear flow behaviour and sluggish relaxation dynamics in entangled polymers are interpreted by a disentanglement process. This molecular interpretation has never been validated by direct observation. We report here on in situ observations of polymer melts under steady-state shear flow using neutron scattering and particle tracking velocimetry. It is shown that the chains remain largely undeformed under steady-state shear flow whereas wall slippage and shear-banding are identified in both entangled and unentangled polymer melts. These observations are of prime importance; they reveal that the flow mechanism and its viscoelastic signature reflect a collective effect and not properties of individual chains.
authors.affiliation: Laboratoire Léon Brillouin (CEA-CNRS), CE-Saclay, 91191 Gif-sur-Yvette, Cedex, France. laurence.noirez@cea.fr.
authors.forename: Laurence
authors.initials: L
authors.lastname: Noirez
authors.forename: Hakima
authors.initials: H
authors.lastname: Mendil-Jakani
authors.forename: Patrick
authors.initials: P
authors.lastname: Baroni