Entangled Polymer Melts in Extensional Flow - Characterization by Combined Rheology and Small-Angle Neutron Scattering

Liquid bridges occur in a variety of situations in nature - yet our understanding of the dynamics and stability is very limited. Examples of liquid bridges are the process used byspiders to form draglines and the process used by cats lapping milk. We have an extendedprogram aiming to provide generic knowledge about the process in which macromolecular fluidfilaments are extended and stretched and show how the extensional properties are related to theproperties on individual molecules. We combine structural and rheological studies of a series ofmodel polymers with different composition and architectures. The project entails synthesizingmodel polymer systems of precisely known molecular architecture, subjecting these materials tocontrolled extensional flows and to measure the molecular deformation under controlled flowsituation by SANS. Neutron contrast is obtained using specific deuterium labeled molecules.We have targeted different systems: first a “simple” sample of homogeneous high-molar masspolymers, where only the central part of a fraction of the polymers were D-labelled with the aimto highlight the polymer deformation and avoid influence of fast relaxation near the polymerends [1]. Another example is a bimodal mixture of linear polymer chains with respectively highand low molar mass, and we have studied samples with more complex geometry, includingPOM-POM architecture. The 2D-SANS data have typically Lozenge shaped contour which isanalyzed using the Read- McLeish-model of stretched polymer network [2]. The structure andrheology are measured both as a function of stain flow velocity, final Hencky strain ratio andduring the relaxation after cessation of extensional flow.