The packing of granular polymer chains
Original entry: Sujit S. Datta, APPHY 225, Fall 2009.
L. N. Zhou, X. Cheng, M. L. Rivers, H. M. Jaeger and S. R. Nagel, Science 326, 408 (2009).
A major thrust of soft matter physics research in the past decade has been to elucidate the nature of "jamming", the manner in which various soft materials transition to a state in which they are rigid and resistant to shear. This is generally thought to be tuned by shear stress, temperature, or packing density, in a manner that is thought to be common to a wide variety of materials (colloidal suspensions, powders and grains, or polymer melts, for example). Random packings of athermal spheres, for example, can be rigid and resistant to shear at large enough packing densities. Polymer melts, on the other hand, can also quickly transition to a jammed or "glassy" state at sufficiently low temperatures. While both of these transitions have been thoroughly explored independently, very little work draws explicit connections between the two. This paper reports on experiments studying the packing of flexible granular chains (structurally similar to polymers), and the manner in which they jam. Interestingly, this transition seems to have much in common with the polymeric glass transition, thus suggesting universal behavior in the manner in which granular systems and polymer melts "jam".
- How do flexible granular chains jam?
- Find: as chain length increases, density and coordination number decreases -- but, still jammed
- Long floppy chains partition into groups of small loops (which have more rigidity) that then jam
- Strengthens possible connection between jamming of granular materials and polymeric glass transition: similar dependence on chain length, topology, stiffness