Abstract:

Wormlike micelles, as quintessential soft matter systems, have garnered substantial interest across industrial and biomedical sectors due to their unique viscoelastic signatures and reversible, dynamic network architectures. This review provides a comprehensive examination of the steady flow behaviors of these self-assembled structures, with a focus on the intricate interplay between microstructural evolution and macroscopic responses under both shear and extensional deformations. Under shear flow, wormlike micellar solutions exhibit a characteristic multi-regime flow curve, encompassing a Newtonian plateau, a shear-thinning region, and, at extreme rates, a second plateau. The zero-shear viscosity scales as a power-law with surfactant concentration, offering critical insights into micellar growth, the onset of entanglement, and the eventual formation of branched networks. In contrast, extensional flow elicits markedly different nonlinear responses, such as strain hardening, tensile failure, and subsequent dynamic recovery. These distinctions underscore the dominant role of chain flexibility and reversible scission in dictating the rheological response under different kinematic conditions. A focal point of this review is the phenomenon of shear banding, an archetypal flow instability arising from a dynamic mismatch between localized network disentanglement and re-entanglement. This symmetry-breaking process, manifesting as coexisting regions of differing shear rates, is intrinsically linked to a non-monotonic constitutive relation and reveals a fundamental structural fragility inherent to “living” polymer assemblies. Finally, we delineate the prevailing challenges in the field and propose future directions. Emphasis is placed on the development of in-situ characterization techniques, the formulation of advanced constitutive models that capture the unique dynamics of these systems, and the exploration of their behavior under complex, application-relevant conditions. Such endeavors are essential for advancing the non-equilibrium physics of soft materials and for guiding the rational design of functional fluids for advanced technologies.

Key words: wormlike micelles, steady shear rheology, extensional rheology, shear banding, shear thinning