Shear-induced migration of confined flexible fibers

We report an experimental study of the shear-induced migration of flexible fibers in suspensions confined between two parallel plates. Non-Brownian fiber suspensions are imaged in a rheo-microscopy setup, where the top and the bottom plates counter-rotate and create a Couette flow. Initially, the fibers are near the bottom plate due to sedimentation. Under shear, the fibers move with the flow and migrate towards the center plane between the two walls. Statistical properties of the fibers, such as the mean values of the positions, orientations, and end-to-end lengths of the fibers, are used to characterize the behaviors of the fibers. A dimensionless parameter ?(eff), which compares the hydrodynamic shear stress and the fiber stiffness, is used to analyze the effective flexibility of the fibers. The observations show that the fibers that are more likely to bend exhibit faster migration. As ?(eff) increases (softer fibers and stronger shear stresses), the fibers tend to align in the flow direction and the motions of the fibers transition from tumbling and rolling to bending. The bending fibers drift away from the walls to the center plane. Further increasing ?(eff) leads to more coiled fiber shapes, and the bending is more frequent and with larger magnitudes, which leads to more rapid migration towards the center. Different behaviors of the fibers are quantified with ?(eff), and the structures and the dynamics of the fibers are correlated with the migration.

Automated summary

The experimental study investigates the shear-induced migration of flexible fibers in suspensions confined between two parallel plates. The migration of fibers is found to be related to their flexibility and the shear stress, with softer fibers and stronger shear stresses leading to faster migration. As the dimensionless parameter ?(eff) increases, fibers tend to align in the flow direction and exhibit more bending behavior towards the center plane.