Switchable bistable ordering and real-time alignment dynamics in wormlike micelles

Abstract

Using a combination of rheology and magnetic resonance known as “rheo-NMR” we observe, in real time, the shear- and field-dependent dynamics of orientational order in a wormlike micelle (WLM). We construct a dynamical phase diagram, yielding a range where bistable shear-activated phase switching occurs in which WLMs are stably isotropic (> 12 h) before shearing, and yet realign with B₀ after shearing. Furthermore, we extract anisotropic viscoelastic coefficients for the first time in a WLM by precisely fitting nonlinear realignment data. This deepened understanding of complex surfactant fluid dynamics lights a path toward increased materials control in advanced lubricants and coatings, drug delivery, and tissue engineering.