Measuring the coordination number and entropy of a 3D jammed emulsion packing by confocal microscopy.

Jammed matter is by definition impenetrable to light, such that little is known about the geometry of jammed systems. Using confocal microscopy to image an emulsion in 3D, we first explain the origin of the enhanced fluorescence at the droplet contacts and then determine the contact network inside the model frictionless system. This enables the experimental determination of the average coordination number <Z> which agrees with the isostatic predicted value of <Z> approximately 6. Furthermore, we calculate the entropy of the packing from the network of contacts.