Letter to the editor: Cone partitioned plate (CPP) vs circular couette

Abstract

In geometries capable of producing uniform shear stress across the gap such as cone–plate, it is a challenge to study the nonlinear rheology of well-entangled polymers without wall slip and edge fracture. The task to obtain meaningful steady-state information is particularly daunting. Significant insights are required in the design of experiments and choice of reliable apparatuses that could fulfill the objective to determine the constitutive behavior. In a recent published article, Hu J. Rheol. 54, 1307–1323 (2010) reported particle-imaging velocimetric measurements of two highly entangled polybutadiene solutions with a cocylinder geometry. One of the solutions was prepared and provided to Hu by Ravindranath from the University of Akron. Rheological and particletracking velocimetric studies have been carried out on the same sample in our laboratory. In this letter, we will compare Hu’s results with our own measurements, clarify a few misrepresentations, and discuss several important issues concerning shear banding in entangled polymers.