Strain localization during squeeze of an entangled polymer melt under constant force

We explore the nonlinear rheological behavior of an entangled melt under one-dimensional squeeze at constant squeezing force. In the absence of any meniscus failure, we find according to the particle-tracking velocimetric observations that the nonlinear response during creep takes place through strain localization. Specifically, the creep is observed to speed up due to the reduced viscosity that first takes place at the polymer/wall interface. Apart from the massive apparent wall slip, the particle-tracking velocimetry reveals strain localization in the bulk, presumably due to localized yielding of the entanglement network. Thus, the combination of rheometric information and knowledge about the strain field has illustrated a common feature concerning the nonlinear response of well-entangled polymers to large deformation, i.e., shear banding during yielding. (C) 2018 The Society of Rheology.