N rmal Stress Differences in Polymers During Shear Flow

I. INTRODUCTION Normal stresses were defined in Chap. I. Unequal normal stresses in shear flow are not found with Newtonian liquids but are characteristic of non-Newtonian polymer melts and solutions. Normal stress differences are primarily manifestations of the elasticity of polymeric materials. and this elasticiry results from the orientation and extension of polymer chain segments. Chain extension and orientation is aided by the presence of entanglements and results in the storage of energy within the polymeric fluid.