HOW DO POLYMERS STRETCH IN STAGNATION POINT EXTENSIONAL FLOW-FIELDS

In this paper we present an analysis of salient existing evidence on t he nature of the coil-stretch transition for dilute polymer solutions in extensional flows around stagnation points. Some experiments suppor t the idea of a transition which is critical in strain-rate to a highl y extended final state, other studies report a non-critical extension and only a low degree of final strain. This situation is mirrored by t heoretical and computational approaches, where the existence of a crit ical transition has long been a controversy. We also present new exper imental evidence which leads us to maintain our previous arguments for criticality of the transition and close to full stretching.