Jamming of Ultra-low Density Brownian Rods

Jamming describes a transition from a flowing state to an arrested, rigid, and amorphous state. At critical values of the packing fraction long, thin rods undergo a jamming transition. Furthermore, such rods cannot be isotopically packed above a critical density that scales inversely with the rod aspect ratio. Prior work studied the jamming of granular rod-like systems where thermal fluctuations were irrelevant to the dynamics of the system. We experimentally study the jamming of ultra-low density Brownian rigid rods with millimeter persistence length. To overcome the previous limits on generating high-density isotropic suspensions, we prepare our suspension by polymerizing rods in situ from monomers. The rod aspect ratio can be tuned from 250 to 5000 by controlling the stoichiometry of the polymerization reaction. Beyond a critical density or the aspect ratio, the rods arrest into a solid jammed structure that exhibits solid-like rheology and lacks any local nematic ordering. The jammed isotropic rods yield and locally align above critical stress, with their elasticity dropping by almost 4 orders of magnitude.