Capillary-driven dynamics of fiber bundles aggregation

Long fibers, with their high aspect ratio, exhibit the fascinating phenomenon of wet fiber clustering during evaporation, even in liquids with low surface tension. Here, we theoretically and experimentally investigate the elastohydrodynamic interactions within fibrous media by examining the shrinkage dynamics of fiber bundles during withdrawal from a liquid reservoir. We immerse and then withdraw them from liquid, observing the assembly of fibers. During withdrawal, water is trapped within the fiber bundle by viscous resistance. Once removed, the fibers start to cluster together as the retained water is expelled due to capillary pressure. Our experiments reveal that the shrinkage dynamics of the bundle diameter are influenced by various parameters: withdrawal velocity, surface tension, viscosity, and fiber spacing and length. Based on the experimental study, we develop a theoretical model that encapsulates the drainage dynamics, enhancing the understanding of fluid-structure interactions in fibrous media.