Probing Flow-Induced Chain Scission in Shear-Banding Wormlike Micelles

We investigate the microstructural dynamics of wormlike micellar (WLM) solutions based on CPyCl/NaSal/D${}_2$O under shear flow using spatially resolved rheo-diffusion NMR, velocity-compensated diffusion measurements, and rheo-optical imaging in a Taylor–Couette geometry. Two viscoelastic systems were examined: a non-shear-banding WLM with a molar salt-surfactant concentration ratio of $R=0.4$ and a shear-banding WLM with $R=0.53$. Rheo-optical and velocity measurements confirm homogeneous flow for the non-shear-banding system and the coexistence of low- and high-shear bands within the stress-plateau regime for the shear-banding system. Despite the pronounced heterogeneity in velocity and shear rate associated with shear banding, the local surfactant self-diffusivity remains spatially uniform across the gap and throughout the stress-plateau regime. Furthermore, analysis of the mean-squared-displacement scaling reveals no measurable difference between the high- and low-shear bands. These results demonstrate that the micellar microstructure remains largely unchanged despite the formation of shear bands and provide direct experimental evidence that flow-induced micellar chain scission is not a dominant mechanism governing shear banding in this WLM system.