Nonlinear Extensional Behavior of Bidsperse Polymer Melts

Recent particle tracking velocimetric (PTV) observations have allowed a phenomenological framework to be established for nonlinear rheology of monodisperse polymer melts both for shear [e.g. Macromolecules 44, 183 (2011)] and extension [J. Rheol. 52, 1275 (2008)].  In particular, we have explored the phenomena of strain localization after yielding [J. Chem. Phys. 127, 064903 (2007); J. Rheol. 53, 1389 (2009)] for monodisperse polymers.  The present work investigates bidisperse melts made with 50% high molecular weight styrene butadiene rubber (SBR) and 50% low molecular weight (SBR), subjecting them to both simple shear including capillary rheometry and uniaxial extension.  We will determine (a) whether the double network would take turns in providing structural integrity during extension and (b) whether wall slip can be suppressed.  In particular, we will search for conditions necessary to produce stable necking during uniaxial stretching and develop new insight into the physics governing strain localization in fast large deformation of entangled polymers.