Coiling of an elastic beam inside a disk: A model for spider-capture silk

•Spider-capture fibers are very extensible. These fibers are decorated with liquid drops.•We show that this is due to the presence of coils of fiber inside the drops.•Capillary forces are responsible for the buckling and coiling of the fiber.•We experimentally reproduce the coiling with synthetic fibers.•We provide theoretical and numerical analysis of the experiments.

Motivated by recent experimental observations of capillary-induced spooling of fibers inside droplets both in spider capture silk and in synthetic systems, we investigate the behavior of a fiber packed in a drop. Using a simplified 2D model, we provide analytical predictions for the buckling threshold and the deep post-buckling asymptotic behavior. The threshold for spooling is found to be in particularly good agreement with experimental results. We further solve the Elastica equations for a fiber confined in a soft potential, and track the equilibrium paths using numerical continuation techniques. A wealth of different paths corresponding to different symmetries is uncovered, and their stability is finally discussed.