Jamming

Jamming

We use confocal microscopy to study the structure and mechanical properties of spherical colloids, such as emulsions and polymeric particles. We pioneered the use of fluorescently labeled systems to study the distribution of stresses in compressed emulsions by mapping out the contact network. By refractive index matching, this approach provides a window into the 3D microstructure and topology of particle packings (e.g., seen at right) including the coordination number distribution, packing density, diversity of configurations, and the relationship between the microstructure and macroscopic properties.

In prior work, it was shown that spherical particles indeed pack with an average coordination number of 6, in accordance with the theory of isostaticity, and a method was devised for calculating the configurational entropy of the system from the network of contacts within the dense packing. We have extended these confocal microscopy measurements to characterize 3D assemblies of fluorescently labelled PMMA particles. Using the interparticle contact area under deformation measured with confocal methods together with the known modulus of the colloidal particles, we can determing interparticle forces, their distribution, and the stress transmission isotropy (force chains) through particulate matter under different packing and stress conditions.

Attractive emulsion droplets probe the phase diagram of jammed granular matter
PNAS, 108, 11 (2011)
I. Jorjadze, L. Pontani, K. A. Newhall, J. Brujic
Jammed particles, from sandy beaches to sunscreens
Physics Today, 63, 11, 64-65 (2010)
J. Brujic
A 'granocentric' model for random packing of jammed emulsions
Nature 460, 611-615 (30 July 2009)
Maxime Clusel, Eric I. Corwin, Alexander O. N. Siemens, Jasna Brujic