The molecular origin of stress generation in worm-like micelles, using a rheo-SANS LAOS approach

We combine large-amplitude oscillatory shear (LAOS) and time-resolved small angle neutron scattering (t-SANS) measurements on the dynamic response of a dispersion of surfactant worm-like micelles. By viewing the response as being the result of a sequence of physical processes, we observe new features of the system response. We identify three distinct frequency regimes including a high frequency Maxwell-like, a yielding, and a settled flow regime. For each regime we identify the molecular origins, on a Kuhn segment scale, of the stress response. We show the ability of the material to 'over-orient' pre-yielding, compared with stationary flow. Finally, we present a stress-orientation rule which is rate-based at low frequencies and strain-based at high frequencies.