Step Shear of Entangled Linear Polymer Melts: New Experimental Evidence for Elastic Yielding

This work studies the most basic and important behavior of entangled linear polymer melts in sudden large shear deformations. In particular, melt elasticity resulting from the large step shear is extensively shown to produce cohesive breakdown. Unlike entangled solutions studied in Macromolecules 2007,40, 8031, the residual elastic forces in sheared melts struggle quiescently for a significant induction period before bringing down the entanglement network. The induction time for the elastic yielding can be much longer than the longest Rouse relaxation time iota(R), making it difficult to associate this cohesive failure with a chain retraction process envisioned in the tube theory. The cohesive failure also occurs upon a step strain produced at rates too slow to produce chain stretching, again making it unreasonable to invoke the concept of chain retraction due to chain stretching.