Understanding and predicting flow instabilities in self-assembled polymers

Shear banding flow instabilities are common in wormlike micelles (WLMs). Despite reported shear banding in polymer WLMs (pWLMs), current research has focused on surfactant WLMs (sWLMs) or linear polymers. Shear banding in linear polymers is typically transient, unstable, or an artifact of slip, fracture, or geometry; conversely, sWLMs dynamically rearrange and break, enabling steady state shear banding. As breakage in pWLMs is limited, the shear banding characteristics likely fall between these limiting cases, though this behavior remains largely unexplored. Here, we use nonlinear rheology and small angle neutron scattering (SANS) to systematically evaluate pWLM shear banding in commercial triblock poloxamers, where the molecular weight, block length, and block ratios are well-controlled. Poloxamer characteristics and micelle features identified via linear rheology and SANS are then used to develop guidelines to predict shear banding a priori, where important parameters include micelle dimensions, solvent penetration, and entanglement degree, among others. Understanding the fundamental role of poloxamer subunit and self-assembled structure provides insight into shear banding mechanisms absent significant breakage, which can be widely used to predict instability formation.