FAST-FLOW BEHAVIOR OF HIGHLY ENTANGLED MONODISPERSE POLYMERS 1 - INTERFACIAL STICK-SLIP TRANSITION OF POLYBUTADIENE MELTS

A systematic experimental investigation is carried out to clarify the nature of a well-known capillary flow phenomenon in linear monodispers e polybutadienes (PBd). By varying the surface condition and the,die d iameter, it is alluded that a spurt-like stick-slip transition actuall y results from a breakdown of chain entanglement between adsorbed and next-layer unbound chains. In other words, the transition is not a man ifestation of any constitutive properties, as previously asserted by V inogradov and coworkers (1984). The melt viscosity dependence of the t ransition amplitude agrees with a Navier-de Gennes type analysis of wa ll slip. A comparison between the-capillary flow and dynamic shear beh avior of the same monodisperse PBd reveals that the interfacial stick- slip transition occurs at a stress level that is only a third of the p lateau stress given by the elastic plateau modulus G(N)(0) = 1.0 MPa a t 40 degrees C. The molecular weight independence of the critical stre ss for the transition provides a striking contrast with the transition characteristics observed in linear polyethylenes and suggests a diffe rent state of PBd chain adsorption on steel surfaces.