Probing Shear-Banding Transitions of the VCM Model for Entangled Wormlike Micellar Solutions Using Large Amplitude Oscillatory Shearing (LAOS) Deformations

By Lin Zhou, L.Pamela Cook, Gareth H. McKinley

We explore the use of Large Amplitude Oscillatory Shear (LAOS) deformation to probe the dynamics of shear-banding in soft entangled materials, primarily wormlike
micellar solutions which are prone to breakage and disentanglement under strong deformations. The state of stress in these complex fluids is described by a class of viscoelastic
constitutive models which capture the key linear and nonlinear rheological features of wormlike micellar solutions, including the breakage and reforming of an entangled network. At a frequency-dependent critical strain, the imposed deformation field localizes to form a shear band, with a phase response that depends on the frequency and amplitude of the forcing. The different material responses are compactly represented in the form of Lissajous (phase plane) orbits and a corresponding strain-rate and frequency-dependent Pipkin diagram. Comparisons between the full network model predictions and those of a simpler, limiting case are presented. 

Key words: LAOS, Pipkin diagram, shear banding