Yeonsu Jung
jung [at] seas.harvard.edu
X-Ray Tomography of Entangled Rod Packings
Volumetric imaging experiments that reveal the hidden three-dimensional architecture of entangled fiber assemblies.
Motivation
The mechanical behavior of an entangled rod packing is set by geometry that is invisible from the outside: how each filament curves, who touches whom, and which rods cage which. To test our theory of the entanglement transition (PNAS 2025) against reality, we needed the full 3D configuration of real packings — so we imaged them with X-ray micro-computed tomography.
What we did
- Prepared random packings of flexible rods across a range of aspect ratios and packing fractions
- Acquired micro-CT scans of each packing at the Harvard Center for Nanoscale Systems
- Reconstructed every individual rod centerline from the volumetric data using a custom segmentation pipeline
- Extracted contact networks, crossing numbers, and caging statistics directly from the reconstructed geometry
Why it matters
The reconstructed configurations let us validate simulations against experiments state by state, not just through bulk averages. The same experimental geometry seeded our simulations and our topological analysis, closing the loop between fabrication, imaging, and modeling — and confirming that the onset of collective rigidity coincides with the geometric caging predicted by theory.