(262a) Flow Induced Scission Does Not Explain Shear Banding in Wormlike Micelles (the ‘Living Rolie Poly’ model)

Some systems of well entangled wormlike micelles are known to exhibit shear banding instabilities under strong flow conditions. The underlying mechanism for shear banding may vary with a system's chemical details, and it has been hypothesized that in some cases shear banding emerges as a result of flow-induced scission. The hypothesis is simply stated and seemingly reasonable: when long micelles become sufficiently stressed in flow, they break into shorter chains with less stress - thus the amount of stress the system can support decreases with increasing shear rate and shear banding occurs. However, the constitutive model that supports this picture has a number of notable weaknesses, including (1) an incomplete resolution of the molecular weight distribution and (2) omission of important non-linear stress relaxation processes. In this talk we present an improved constitutive model, the ‘Living Rolie Poly’ model, as a means of addressing these concerns. We use population balance methods to describe how reactions redistribute stress across the entire molecular weight distribution, and we use the Rolie Poly constitutive equation to describe non-linear stress relaxation processes (e.g. chain retraction and convective constraint release) taking place in each sector of the molecular weight distribution. With these improvements, our model provides clear evidence that flow-induced scission alone is not sufficient to explain observations of shear banding in well entangled wormlike micelles.