Interactions of fibers with pillars: from one pillar to pillar arrays

The transport dynamics of flexible fibers in complex environments like porous media underpin numerous industrial and biomedical processes. The complex dynamics of these flexible fibers stem from the presence of obstacles that disturb the fluid flow, their inherent deformability, and potential interactions with obstacles. In our work, we combine experimental and numerical methods first to investigate the dynamics of a flexible fiber interacting with an individual triangle pillar. Owing to their flexibility, fibers tend to deform and align with streamlines, causing negligible lateral displacement pre- and post-pillar. In contrast, the fibers exhibit much richer dynamics in circular pillar arrays, with different lateral drift angles for varying fiber lengths. This separation effect, based on fiber lengths, relates to the flow field distribution and various fiber dynamics in the array. Our research identifies an effective method for length-based flexible fiber sorting in microfluidic applications.