Shear induced micellar chains scission and shear banding in wormlike micellar fluids

Shear banding is a phenomenon in which distinct bands with different local shear rates form under the same applied shear stress. These discontinuities in velocity gradients have been extensively studied in wormlike micellar solutions (WLMs), which serve as model systems for understanding complex fluid behavior. A long-standing hypothesis suggests that shear banding in WLMs arises from flow-induced micellar chain scission, but direct experimental evidence supporting or refuting this mechanism has been limited. In this study, we employ a spatiotemporally resolved Rheo-DOSY-NMR approach, complemented by rheo-optical techniques, to investigate shear banding in CPyCl/NaSal WLMs in a Taylor-Couette (TC) flow. To test the micellar breakage hypothesis, we first measure the self-diffusivity of surfactants in quiescent micellar solutions and confirm that as micelle length increases, diffusivity decreases, finding a correlation between micellar length and diffusivity. We then conduct spatially resolved diffusivity measurements under shear across the TC cell gap over a wide range of imposed Weissenberg numbers, both below the onset of shear banding and within the stress plateau regime. Our results reveal that self-diffusivity remains unchanged across the shear-banded state, with no distinct differences between the high and low shear bands. This finding suggests that micellar length remains constant during shear banding flows.