Abstract

Macroscale chains have been proposed to provide insight into the physics of molecular polymer systems and have been suggested as a paradigm for understanding physics at the molecular scale. Nevertheless, understanding the rheological response of systems composed of quasi-one-dimensional semiflexible materials, such as spaghetti, remains a significant challenge. We study the nonlinear rheology of random assemblies of macroscale chains, including steel bead chains and cooked spaghetti, under oscillatory shear. We show that a universal transition from localized to wide shear zones occurs upon increasing the strain amplitude, across a wide range of lengths, flexibilities, and other structural parameters of the constituent elements. The critical strain amplitude coincides with the onset of strain stiffening in the system. We derive scaling laws for transition sharpness, shear-zone width, and stiffness enhancement as functions of chain length. Our findings suggest that the entanglements between the constituent elements strengthen when approaching the critical strain amplitude and rapidly become long-range, even spanning the entire finite system for sufficiently long chains. We demonstrate that the nonlinear rheological response is governed by the interplay between increasing stored elastic forces due to entanglements and the increasing contribution of dissipation with shear rate and interlocking between chains. Our results highlight both the differences and similarities between the physics of macroscale chains and molecular polymer systems.