Shearbanding

Shearbanding is a phenomenon observed in certain complex fluids where the material spontaneously forms localized bands of high shear rate separated by regions of very low shear rate, even when subjected to a uniform macroscopic shear. This behavior is distinct from simple shear flow where the deformation is distributed uniformly throughout the material. Shearbanding can occur in a wide range of materials, including polymers, colloidal suspensions, emulsions, and even some biological fluids like mucus.

The underlying mechanism for shearbanding is typically attributed to the presence of microstructural rearrangements within the fluid. These rearrangements can involve the alignment, breakup, or aggregation of constituent elements like polymer chains or colloidal particles. As the shear rate increases, a critical point is reached where the fluid's microstructure becomes unstable. This instability leads to the formation of distinct regions with different degrees of structural organization and consequently, different rheological properties. One region might be highly deformed and flowing readily, while the adjacent region remains largely undeformed.

The onset of shearbanding is often characterized by a non-monotonic relationship between shear stress and shear rate, where the stress may plateau or even decrease as the shear rate increases beyond a certain point. This can lead to interesting macroscopic observations, such as the appearance of distinct flow patterns or streaks within the bulk fluid. Understanding shearbanding is crucial in various industrial applications, including the processing of plastics, paints, and food products, where controlling flow behavior is essential for product quality and manufacturing efficiency.