Rheo-Optical Evidence of CCR in an Entangled Four-Arm Star

Abstract

We present a model to describe the response of entangled star polymers to steady shear flow. The central ingredient of this model is the inclusion, in a simplified way, of convective constraint release once the shear rate reaches the inverse of the longest relaxation time. Rheo-optical measurements for a solution of four-arm polybutadiene stars demonstrate the efficacy of this model in capturing the salient features of the stars' response as measured by the shear stress and first normal stress difference. These results demonstrate the necessity of including convective constraint release in any model used to describe the nonlinear behavior of stars. Models and experimental results for flows of stars other than steady shear are the subject of ongoing work.