The packing of granular polymer chains

TL;DR

This paper investigates how flexible chains made of hard spheres pack in disordered structures, revealing that backbone rigidity and loop formation influence stability and draw parallels to polymer glass transitions.

Contribution

It introduces a novel understanding of chain packing mechanics, highlighting the role of backbone and loop formation in disordered packings.

Findings

Long chains form low-density, rigid structures primarily supported by the backbone.

Compaction leads to the formation of semi-rigid loops along the chains.

The packing behavior shows similarities to the glass transition in polymers.

Abstract

Rigid particles pack into structures, such as sand dunes on the beach, whose overall stability is determined by the average number of contacts between particles. However, when packing spatially extended objects with flexible shapes, additional concepts must be invoked to understand the stability of the resulting structure. Here we study the disordered packing of chains constructed out of flexibly-connected hard spheres. Using X-ray tomography, we find long chains pack into a low-density structure whose mechanical rigidity is mainly provided by the backbone. On compaction, randomly-oriented, semi-rigid loops form along the chain, and the packing of chains can be understood as the jamming of these elements. Finally we uncover close similarities between the packing of chains and the glass transition in polymers.